Home

Here - Computer and Information Science

1. The cursor indicated as O will appear after the question mark in the last line Typing x will terminate TEX Typing Ctl c will have the same effect on some systems while it may have no effect at all on other systems Another type of mistake is contained the following file called say first2 tex namely the control sequence bye at the end of the file is missing This is Tex 21 MATHEMATICAL TYPESETTING 81 When one runs TFX on this file the following message is produced This is TeX Version 3 1415 C version 6 1 first2 tex The asterisk indicates that T X can accept input from the keyboard The missing control sequence bye can now be typed this will make T X terminate gracefully A third type of mistake appears in the following file called first tez input mastex This is TeX bye The first line of this file instructs T X to take input from a file called mastez tex located either in the present directory or in some other directory that TEX knows about there is however no file called mastex ter The following message is pro duced This is TeX Version 3 1415 C version 6 1 first3 tex I can t find file mastex 1 1 input mastex Please type another input file name Here one could type the name of the file that is actually desired it may happen however that there is no such file for example it is anticipated that the file will be c
2. 488 488 488 488 488 488 122 122 122 122 122 122 984 984 984 984 984 984 984 INDEX INDEX amp see ampersand amp A 71 40 51 asterisk in TEX see TeX asterisk in wildcard in filenames see file name wildcard in see character backslash 80 cursor 43 lt less than or equal to in Pascal 44 a 71 V 71 sign in TEX see TFX per cent sign in see pound sign u space character 14 43 X 47 tilde escape in email 89 user s home directory 10 a out 37 Adobe Corporation 79 Aho Alfred V 107 ATX 6 alias mail 88 shell 121 America Online 127 131 American Mathematical Soci ety 83 American Standard Code for Information Interchange see ASCII ampersand amp 20 124 AMS see American Mathe matical Society AMS TEX see TEX AMS TEx amsppt see TEX AMS Preprint Style and in Pascal see Pascal key word and arithmetic Fundamental Theorem of 67 69 arithmetic expression in Pas cal see Pascal arithmetic expression in arithmetic operators in Pas cal see Pascal operators in arithmetic array in Pascal see Pascal key word array ASCII 8 ASCII file see file ASCII assignment in Pascal see Pascal assignment in asterisk in T X see TFX as terisk in Atrium 8 Computer Laboratory at Brooklyn College 8 132 INDEX Web site
3. 5 writeln 6 a true 7 repeat 70 IV APPLICATIONS OF PASCAL 8 result not a 9 writeln a 1 gt result 1 10 a nota 11 until a 12 end This program prints the following 21 A not A 22 23 T F 24 F T The numbers on the left are line numbers and are not part of the program or the printout We numbered the lines in the printout beginning with 21 so we can easily refer to lines both in the program and in the printout In line 2 of the program the variables a and result are declared to be of type boolean these are variables that can assume only the values True and False The first line line 21 of the printout is printed in line 4 the number of spaces in quotes have to be carefully adjusted to get a nice printout The effect of the writeln statement in line 5 is to print a blank i e empty line this is line 22 The repeat statement in lines 7 11 is similar to the while statement considered above but it works somewhat differently Its syntax is repeat list of statements until condition Here list of statements refers to one or more statements separated by semicolons there should be no semicolon after the last statement At present the list of state ments consist of the three statements in lines 8 10 and the condition is the boolean variable a since a boolean variable can be either true or false the condition will be satisfied if this variable is true The meaning of the repeat statement is as
4. It is not hard to see that every positive integer greater than one can be written as a product of primes For example 2599443 3 3 7 11 11 11 31 The product on the right hand side is called the prime factorization of the number on the left The only other ways to write the number on the left as a product of primes to write the same primes in a different order e g 2599443 7 3 31 11 3 11 11 but since changing the order of factors will not change the product this prime factorization is not essentially different The fact that a positive can be written only one way as a product of primes aside from the order of factors is called the Fundamental Theorem of Arithmetic It can formally be stated as THE FUNDAMENTAL THEOREM OF ARITHMETIC The prime factorization of every integer greater than one is unique aside from the order of factors The key result needed in order to prove this is the following lemma described by Euclid Euclid however does not mention the Fundamental Theorem of Arithmetic itself the Fundamental Theorem was first formulated and proved by the German mathematician Karl Friedrich Gauss in 1801 even though it had been used long before 68 IV APPLICATIONS OF PASCAL LEMMA Let a and b be integers and let p be a prime If ab is divisible by p then either a is divisible by p or b is divisible by p Note that in mathematics or is always used in the inclusive sense that is the possibility that both a a
5. You can use numbers with some of the above commands For example typing y3w will yank put into the unnamed buffer three words and 2Y will yank two lines Capital Lock key Unix commands including vi are case sensitive Acciden tally pressing the Capital Lock key on the keyboard represent a special danger in vi The commands meant to be typed in lower case cannot by typed in upper case and typing them in upper case accidentally can cause serious damage to the file in a few key strokes Therefore you need to exercise special care that you do not press the Capital Lock key inadvertently Editing commands The command fc allows you to repeat the last command you typed possibly in an improved form Suppose you typed the command cp problem you will get an error message The message is different for various Unix systems it could be something like cp missing destination file Try cp help for more information in Linux or cp Insufficient arguments 1 Usage cp f i p f1 f2 cp f i p f1 fn di cp riR f i p di dn 1 dn in Solaris The problem is of course the missing second argument since the com mand should look something like cp problem question This command will copy the content of the file problem to a file called question which may be a new file which then is created or an old file in which case the old content is destroyed The mistyped command can be corrected by typing
6. 1 bin sh 2 cp 1 tex 1_junk tex 3 tex 1_junk 4 cp 1_junk dvi 1 dvi 5 rm 1_junk If you call this file texxing then you can typeset the file whole tex by typing texxing whole The point about this script is that the file whole dvi is only corrupted while the command cp in line 4 is executed and that takes only a small fraction of a second Line 5 removes the files whole_ tex whole_ log and whole_ dvi the latter two were created by the TEX program in the file name the asterisk is matched by any string i e any file whose name starts out as whole_junk and has some additional characters at the end will be removed see p 12 for a discussion of the wild card character asterisk in filenames Note that the fact that the above script works is an idiosyncrasy of the behavior of the program xdvi For example the scripts 1 bin sh 2 cp 1 tex 1_junk tex 3 tex 1_junk 4 cp f 1_junk dvi 1 dvi 5 rm 1_junk and 120 V MISCELLANEA bin sh cp 1 tex 1_junk tex tex 1_junk mv 1_junk dvi 1 dvi 5 rm 1_junk BwWN Fe do not work that is if we repeatedly change the file whole tex and then typeset if by these scripts the display window opened by xdvi will only be updated if we use the first of the above scripts for typesetting and not if we use the second or the third script A perhaps somewhat simplistic explanation might be that the file whole dvi produced by line 4 when the script is run as above
7. 7 8 9 a true b true c true 10 repeat 11 repeat 12 repeat 13 result a and b or not c 14 write a 1 b 1 c 1 15 writeln gt result 1 72 IV APPLICATIONS OF PASCAL 16 cC not c 17 until c 18 b not b 19 until b 20 a nota 21 until a 22 end The printout of this program is as follows 31 A B C result 32 33T T T T 34T T F T SST Eor oF 36T F F T 37 F TT F 38 F T F T 39 F F T F 40 F FFE T Problems 1 As we mentioned in the footnote above the description of the printing of Boolean variables given above only applies to GNU Pascal In Sun Pascal TRUE and FALSE are printed even if the Boolean variables are specified with width 1 This results in misalignments of the tables printed by the programs in the present section when using Sun Pascal Solve the misalignment problem by printing the Boolean variables in the above programs with width 5 width 5 is needed since the word TRUE is contains four letters while the word FALSE contains 5 In order to get a neat alignment in the tables the number of quoted spaces in the write or writeln statements in these programs must be adjusted 2 The misalignment problem in Sun Pascal can also be solved by replacing the writeln statements by longer conditional statements of the type if a then write T else write F Solve the misalignment problem in Sun Pascal by using such conditional statements 20 Day o
8. If a network administrator has to add 25 new users to a Unix network he she can write a shell script that can do this task fast without human intervention In Windows NT adding a user may take about two minutes with a few mouse clicks Adding twenty five users however cannot be speeded up the administrator has to go through the same sequence of mouse clicks 25 times this may change in Windows 2000 the next edition of Windows NT Current trends for making everything GUI in certain operating systems are cer tainly not ideal It would help at least the experienced users if many GUI com mands would have well documented CLI counterparts For example it would be nice if Netscape could be invoked from the command line to collect the ingredients of a Web page without actually displaying it so a number of Web pages could be collected for later perusal at a convenient time without having to wait for slow downloads 24 More Shell Scripts Using Netscape to view HTML files Warning The first few examples presented in this section have security problems on account of using temporary files In a later example we will describe a more secure way of handling temporary files and all these script should be rewritten in conformity with the remarks made on p 113 on account of the symlink attack see there Suppose you have an HTML file in the directory HOME htm1_files example html where HOME refers to your home directory see p 95 above I
9. Noon FF WN 8 the date displayed will of course be the actual date If the file cmuserd already t S Dear Charley Sat Jun 21 21 06 51 EDT 1997 J F Smith jsmith math myschool edu http www math myschool edu jsmith exists and has the following content 1 2 then the content displayed by vi after running the above shell script will be 1 Non FWD I think I can make your suggestion work I have to think about it a little more however ep S Dear Charley Sat Jun 21 21 06 51 EDT 1997 I think I can make your suggestion work I have to think about it a little more however Regards 23 SHELL SCRIPTS 95 9 J F Smith 10 jsmith math myschool edu 11 http www math myschool edu jsmith 12 S To finish the letter the address in line 1 and the subject in line 2 has to be added and a remark may be added after line 12 Next we will explain how the above shell script produces these results The line numbers below will refer to the line numbers in this script i e in the file letter above Line 1 specifies that the Bourne shell is to be used Line 2 adds the content of the file HOME marks regards at the end of the file referred to as 1 i e the first command line argument of the shell script being discussed this argument at present is cmuserd if this latter file is empty then its content will be identical to that of the former file if it is not the new file will have things added at the end her
10. 22 tempx x1 tempy yl 23 xl x q x1 yl y q y1 24 x tempx y tempy 25 end 26 Error check commented out in the final version 27 if b a0 x bO y then 28 writeln The result is correct 29 else 30 writeln The result is not correct 31 writeln b 1 a0 1 x 1 b0 1 y 1 32 end When testing this program it is worth including lines 27 30 At the end of the program the variable b should hold the greatest common divisor of ag and bo and the equation b aox boy 17 PASCAL PROGRAM FOR GCD AS A LINEAR COMBINATION 65 should be satisfied After testing the program sufficiently there is no further need for these lines and so these lines should not be part of the final program However rather than deleting the lines it is a good idea to keep them but to comment them out If on a later occasion the program is modified then these lines can be useful for further testing and they can easily be reinstated uncommented out to use an awkward but useful phrase Of course even if this test is successfully passed the correctness of the above program is not guaranteed and other tests are necessary to be convinced that the program does what it is required to do When we run this program and enter the inputs 422 and 546 for a and b respec tively the printout will be as follows 2 422 22 546 17 This does not look right since 17 should be in parentheses One
11. 50 422 4 546 3 can be symbolically written as b aox boy a agx1 boy where x 1 y 1 z 4 and y 3 We can then write r b aq aox boy g aox1 boyi ao x x1 boly qy 62 IV APPLICATIONS OF PASCAL That is if the equation 24 422 9 546 7 is symbolically written as T Q01 new ay boYt new then we have Zi new T qz and Yinew Y qy Now in the next step of the Euclidean algorithm we will have bnew a 50 and anew r 24 For the next step the old equations 124 422 1 546 1 50 422 4 546 3 or symbolically the equations b aox boy a aor boy will have to be replaced with updated to the new equations 50 422 4 546 3 24 422 9 546 7 which can now be symbolically written as Drew a0 new boYnew Anew Q0T1 new boYt new The update equations for all the new variables have already been given except those for Znew and Ynew These update equations are easy to obtain namely it is clear that the first equation bnew A0Tnew boYnew of the present group is the same as the second equation a ao boys of the earlier group That is we must have Trew and Ynew Y1 We will now summarize these update equations Noting that we calculated r as r b mod a we have anew r a mod b bnew a Tnew T1 Ynew Y1 17 PASCAL PROGRAM FOR GCD A
12. The writeln statements in lines 32 33 and 35 36 were broken up because they are too long to conveniently fit in one line note that the breakup point must be outside the range of the quote signs Problem 1 What is printed by the following program You must be precise you must indicate spaces and you must not include a space where there is no space You may indicate a space by the symbol u 1 program example output 2 var b a0 bO x y integer 3 begin 4 a0 856 bO 962 5 x 118 y 105 6 b 2 7 if x lt 0 then 8 writeln b 1 a0 1 x 1 9 bO 1 y 1 10 else 11 writeln b 1 a0 1 x 1 12 b0 1 y 1 13 end 2 Write a program that performs the extended Euclidean algorithm as above but instead of only printing the equation representing the greatest common divisor as a linear combination it represents all the remainders that come up in the Euclidean algorithm as a linear combination That is if one enters the numbers 546 and 422 as inputs to this program each of the numbers 546 422 124 50 24 and 2 is represented as a linear combination of 422 and 546 see p 60 for these equations Hint The easiest way to write this program is to take the last program of the main text above and moving the statement carrying out the printing inside the loop Note that after moving this statement the indentation needs to be adjusted so
13. Unix provides a powerful open computer operating environment open here means that Unix is not controlled by a single company changes to be made to Unix are discussed out in the open rather than in closed corporate board rooms In fact the source code of a version of Unix called Linux is available for anyone to study and modify whereas for many software companies the source code of programs is a highly valued trade secret Such an openness is especially important in a college environment since computing cannot be properly studied if important parts of the computing environment are not available for inspection Closed proprietary com puting can be useful in a college environment if the computer is strictly a tool to be used and not studied Two interesting Web sites where news items and technical issues involving computers can be found is http www infoworld com and http theregister co uk cf Section 4 on the World Wide Web to see how to look up such Web sites see p 20 especially In Chapter I we give an introduction to Unix This introduction is kept brief only the necessary prerequisites for necessary for efficient file manipulation editing and running programs are discussed Then in Chapter 2 we describe how to write a simple Web page A short introduction to Hypertext Markup Language HTML is given and instructions are given as to how to make a file written in HTML visible for everyone connected to the World Wide Web
14. as like this Enter the first number 153 Enter the second number The second line was printed by the write statement on line 6 the position of the cursor indicated by O here we normally do not show the cursor in these notes indicates that a space was printed at the end of the line If the number 22 is entered now then the program finishes and its printout plus the characters typed by the used will appear as follows Enter the first number 153 44 HI PASCAL Enter the second number 22 The sum of 153 and 22 is 175 11 Loops Next we will consider the following program 1 program example5 input output 2 var i sum n integer 3 begin 4 write Type n n must be a positive integer 5 readlin n 6 7 8 9 i i sum 0 while i lt n do begin 10 sum sum i 11 i i 1 12 end 13 write The sum of integers from 1 through 14 writeln n 1 equals sum 1 15 end This program contains several new features The first one to mention is the com pound statement in lines 9 12 A compound statement is a sequence of statements enclosed between the key words begin and end as we mentioned before there must not be a semicolon before the key word end The purpose using a compound state ment here is to make a sequence of statements appear as a single statement Note that the statement part of the body of the program i e the content of lines 3 15 can also b
15. attributes modify the appearance of these elements in ways specified by their values The attribute BORDER allows us to place a border around the image here the width of the border is specified to be 0 so no border appears the attribute BORDER can be omitted In fact attributes can often be omitted in this case their default value i e the value assumed by the computer are used The image itself is described in the file Matecsm gif located in the directory public_html i e in the same directory in which the file index html being dis cussed is located The file Matecsm gif is a GIF file GIF stands for Graphics Interchange Format The file is produced by scanning a photograph into the com puter it could also have been produced by a digital camera The attribute SRC indicates that this file is the source of the image This attribute is required i e it cannot be omitted The attribute ALT in line 16 introduces the text given in quotes i e Picture that is to be displayed by a text based browser such as lyng which is unable to display images Finally the attribute HSPACE in line 17 places horizontal space of the amount specified by the number 25 on both sides of the image without this horizontal space the image would appear all the way to the left on the page and the text on its right hand side would appear right at the edge of the picture In lines 18 19 the delimiters lt and gt enclose a comment that is a rem
16. b 1 16 end The numbers at the beginning of each line are not part of the program they are added only so that we can easily refer to each line when describing how this program works To give some explanation the numbers a and b are read in in lines 5 and 7 The statements in lines 14 and 15 could have been written as a single writeln statement but then line 14 would have been too long it is easier to break up the statement Even though in the above description we assumed that the number b is always larger than a during the run of this program it is important to note that the program runs correctly even if one enters a larger value for a than for b If for example one enters a 546 and b 422 it is easy to check that after the first execution of the statements in lines 10 12 one will have a 422 and b 546 that is the values of a and b will be interchanged This is because the remainder of the division 422 546 is 422 and its quotient is 0 One can change the above program in a way that this interchange is done explicitly 1 program euclid input output 56 IV APPLICATIONS OF PASCAL 2 vara b temp integer 3 begin 4 write Type a a must be a positive integer 5 readlin a 6 write Type b b must be a positive integer 7 readin b 8 if a gt b then 9 begin 10 temp a 11 a b 12 b temp 13 end 14 while a lt gt 0 do 15 begin 16 temp a 17 a b mod a 18 b t
17. is to write the content of line 7a as a continuation of line 7 and similarly for lines 9a 10a to keep the same line numbers this will not change the meaning of the Pascal program Using line numbers 7a 9a is convenient for us in talking about the inserted statements Observe that it is not permissible to insert a writeln statement directly after line 8 since line 8 must be followed by a single statement which is the compound statement in lines 9 12 If we run this program then it will wait for us at line 5 so that we can enter a number If we enter the number 6 and then press the return key the printout will be as follows 21 Type n n must be a positive integer 6 22 line 7 sum 0 i l 23 line 9 sum 0 i 1 24 line 10 sum 1 i 1 25 line 11 sum 1 i 2 26 line 9 sum 1 i 2 46 HI PASCAL 27 line 10 sum 3 i 2 28 line 11 sum 3 i 3 29 line 9 sum 3 i 3 30 line 10 sum 6 i 3 31 line 11 sum 6 i 4 32 line 9 sum 6 i 4 33 line 10 sum 10 i 4 34 line 11 sum 10 i 5 35 line 9 sum 10 i 5 36 line 10 sum 15 i 5 37 line 11 sum 15 i 6 38 line 9 sum 15 i 6 39 line 10 sum 21 i 6 40 line 11 sum 21 i 7 41 line 12 sum 21 i 7 42 The sum of integers from 1 through 6 equals 21 Again the numbers on the left are line numbers and are not part of the printout We numbered the lines of the printout beginning with line 21 so that we can mix references to lines in the program and the printout wit
18. references by the fact that the character is missing in front From a subdirectory of i e directory contained in usersi jsmith called misc that is from the directory usersi jsmith misc the above file can be identified as euclid seci tex Here is the name of the directory immediately above the present working di rectory i e looked at from usersi jsmith misc the directory means the directory usersi jsmith We add that the the single dot refers to the present working directory that is euclid secl1 tex and euclid seci tex refer to the same file Finally refers refers to the users home directory For example if home cmuser is the home directory of cmuser then the descriptions euclid whole ps and home cmuser euclid whole ps refer to the same files To move between directories you can use the command cd For example if you are in the directory users jsmith then cd euclid changes to the directory users jsmith euclid The command cd users jsmith euclid 1 INTRODUCTION TO USING UNIX 11 changes to this directory from anywhere In case you are in the directory users jsmith misc then you can change to the above directory by typing cd euclid Typing cd in the same directory will move you to the directory users jsmith while typing cd has no effect since refers to the present working directory Finally typing cd alone will usually put you into your home directory T
19. terminal that is to the terminal where the process has been initiated the various names such as tty4 pts 12 etc are names for various terminal names in the output given on p 104 and the question mark indicates that the process has not been initiated at a terminal the third field is the time the process has been active for and the fourth field is the command name associated with the process Note that the items in the first and third field are different in the present in lines 1 2 in the present output from the items involving netscape in the earlier output this is because these commands were issued at different times resulting in different process id s and different activity times Line 4 of the script involves the awk command whose name is made of the initials of its designers Alfred V Aho Brian W Kernighan and Peter J Weinberger The command awk is very powerful and books have been written about it in fact awk is really a programming language rather than just a Unix command Here we have to confine ourselves to explain its specific use given in line 4 of the script The command awk print 1 junkkill0 gt junkkill1 we added the on the left as a prompt to explain how this command works when issued on the command line has as its first and only argument as the file junkki1l0 The awk command goes through this file line by line and with each line it takes the desired action The desired action here is de
20. the file infile for this program may look like as follows 422 546 where the only space character occurring in the file is explicitly indicated as u but one may include extra space and end of line characters that is the following file would also be acceptable as infile i422 UULU 546 If we compare this program with the original Pascal program doing the Euclidean algorithm on p 55 we find that lines 4 and 6 of the earlier program were omitted here indeed these lines were used to warn the interactive user to enter numbers at the keyboard and there is no interactive user at present Furthermore the earlier program used readln instead of the statement read at present The read statement is more flexible since it accepts spaces and end of line characters as separators between items whereas readln always demands an end of line characters after the item s that it reads For this reason if we change lines 6 and 7 in the present program to readln infile a readln infile b then the first version of the file infile will not work because it does not contain an end of line character after the first item to be read In fact if we use the first version infile with the modified version of the present program i e the version containing the readln statement on lines 6 and 7 we get an error message when running the program indicating what is called a run time error i e the program has compiled correctly that is we do not have a compile
21. var log messages is not readable by a regular user you first need to become a superuser to read this file 2 The superuser is a special user with the highest privileges on a Unix machine You can become superuser by typing su whereupon the computer responds with the word Password At this point the you need to type the superuser password which you would have to know but if you have a computer running Unix at home you will have to know the superuser password After becoming superuser the prompt will change from the regular user prompt or whatever the actual prompt is to the superuser prompt or to a more complicated prompt displaying the sign The reason for this is that being a superuser is dangerous and the different prompt is a reminder that one has to be extremely careful One must not do any work on the computer as superuser unless it is absolutely necessary since serious damage can result if mistakes are made Some administration functions can however only be performed as superuser Once becoming superuser you can read the file var log messages by using vi The best way to do this is to type cd var log view var log messages Here indicates the superuser prompt as mentioned just before The command view is the same as vi to look at text files but it prevents you from changing the file more precisely it will allow you to make changes in the file but it will prevent you from saving these changes If you ina
22. with the argument whole of the first of the above three scripts is recognized by xdvi as a new version of the file whole dvi while the files produced by the second and the third scripts are considered new files by xdvi that accidentally bear the same name whole dvi This behavior is easier to understand in case of the third script than in case of the second script and may in fact not be the same for different versions of Unix The behavior of these scripts were tested only in Red Hat Linux 6 0 Removing left over files The following script removes unwanted files that may have been left over accidentally 1 bin sh 2 wunalias rm 2 gt dev null 3 find name core o name junk 4 o name junk o name a out 5 user USER type f 6 exec rm The command find is a very versatile and we cannot explain its main uses here Briefly it finds the files described in the pattern and acts on them the way indicated We will give a more detailed description of the above script The second line unaliases the rm command that is it makes it act the normal way it is supposed to act Shell aliases are explained in the beginning of the next section here we will only say that on occasion the meanings of certain commands are changed often to protect new users such a change of meaning is called aliasing the command rm is one of these commands in a way it is a dangerous command since it re
23. you can check this by using the file command as described above You may get something like bin sh This program substitutes stringi for string2 in file3 ed 3 lt lt 1 s 1 2 g W At this point you are not expected to make sense of this but you can read each individual letter This is a so called shell script a little program that will help you 10 I UNIX accomplish repetitive tasks by automating them The word cat is a shortening of concatenate what this word means is not important at the moment If you want to check which directory you are in you can type pwd pwd stands for print working directory The computer may reply with something like usersi jsmith euclid This means that the directory called often referred to as the root directory contains a directory users1 which contains a directory called jsmith which con tains a directory called euclid This last one is the directory you are currently working If there is a file called secl tex in this directory then that file can be identified together with its location as usersi jsmith euclid sec1 tex This way of referring to a location is called absolute reference to the location There are relative ways to refer to the same file In fact in the directory usersi jsmith euclid this file can simply be referred to as sec1 tex From the directory users1 jsmith this file can be referred to as euclid sec1 tex note that you can recognize relative
24. 10522 10532 with the shell quote character at the end of the line make this command act as if it were typed on the single line That is the command in line 15 kills the processes involving Netscape there are two such processes in the present example but there may be fewer or more such processes in an actual situation kill s 9 is a sure kill see the footnote on p 125 The messages of the command in this line are suppressed by redirecting the standard error output to dev null Line 16 clears Netscape s cache see pp 99 and 21 and line 17 Netscape s lock 24 MORE SHELL SCRIPTS 109 file this must be done since otherwise Netscape cannot be restarted later the lock file of Netscape prevents the user from starting up Netscape again if it is already running Finally line 18 removes the temporary files junkkil1 and junkki110 We called the above script killns The name killnetscape is not suitable since then the command on p 2 of the script would include the information about the pro cess killnetscape itself in the file junkkill0 Then the process killnetscape itself would be killed in line 15 thus lines 16 and 17 would not be executed at all It is not advisable to use the script killns to quit Netscape under normal circum stances The reason is that this may prevent Netscape from taking certain necessary actions For example when you bookmark an item in Netscape the item gets added to your file HOME netsc
25. 19 To move lines 4 7 after the current line 19 type 4 7m19 The command 14r sec2 will copy the contents of the file sec2 after line 14 and the one Or README will copy the contents of the file README at the beginning i e after line 0 of the current file The contents of lines 23 through the last line can be written out to a new file called transfer by typing 23 w transfer Note here that refers to the last line of a file If a file named transfer already exist then this command will not do anything except complain But typing 23 w transfer will replace the current content of the file transfer with the contents of lines 23 through the last line of the file being edited the original content of the file transfer will be lost W simply writes the current state of the file to the memory Until you do this the changes you made to the file are not permanent and you can quit the editor and discard the changes by typing q This will get you back to the command line and you can reenter vi again Typing without the exclamation point will not let you quit the editor if you have made changes in the file without having saved these changes i e without having typed iW afterwards If you want to quit the editor while keeping the changes you made to the file you can do this by typing wq Typing ZZ in command mode will have the same effect Escaping to the shell In many Unix programs the exclamation point is used as
26. a conditional command of the syntax if condition then list of commands else listg of commands fi in shell scripts commands are separated by end of line characters one can use semicolons instead i e the following syntax would also work if condition then list of commands else listz of commands fi Here list of commands is a number of commands separated by end of line characters or semicolons a separator is required even after the last command The semantics 24See the footnote in p 104 discussing the command ps x This works in Linux but other Unices the plural of Unix use different options of ps 112 V MISCELLANEA or meaning of this command is as follows if condition it true then the first list of commands that is list of commands is executed and if condition it false then the second list of commands that is list2 of commands is executed The condition in this command is calculated by the test command in lines 2 4 used to check whether Netscape is running We are about to explain how this command works The command test z string checks whether string in the argument is empty has zero length that is this command returns the value true if the string is empty otherwise it returns the value false The string for this command is provided by line 4 of the script This line is similar to line 3 in the script killnsO on p 109 but there is a key difference As we saw it above line 3 in the script ki
27. advantages That is 20If the present working directory is not listed in the PATH variable then in some Unix systems 24 MORE SHELL SCRIPTS 103 the Netscape command to display the file example html is executed at this point The use of the first period in line 12 to take commands from the file mentioned in this line is called sourcing the file more about this is explained on p 122 The reason for sourcing this file rather than using it as a shell script is that this way we do not have to add execute permission to the file In line 18 the file junknetscape is removed as it is no longer needed Executing a temporary file in a shell script has some hazards and the above script should be considered more as a script used to learn how to write shell scripts than an example for a useful script A more secure way of handling temporary files is to put them into a single temporary directory with appropriately chosen permission codes This is discussed on p 113 Next we will present a slightly improved version of the above shell script Unique names for temporary files in shell scripts Unix is a multitasking system You can simultaneously have several login sessions on the same machine this is especially easy to do if you the machine is networked since you can log into the same machine from different points on the network Or you and a close friend may use your account at the same time This can cause problems with the shell script viewhtml abo
28. an accurate description of the subject helps the recipient in deciding when to read the letter In line 13 indicates the end of the letter what is written after this point will not be transmitted That is line 13 is a comment for the sender of the letter to remind her what the letter is about several lines of comments can be included The recipient will get the part of the letter between lines 3 11 plus a mail header added by the mail program describing where the letter came from how it was transmitted etc There are other tilde escapes c stands for carbon copy the addresses stated on lines introduced by this escape will get a copy of the letter The only difference between recipients of carbon copies and recipients of the letter is what the mail header says about them lines beginning with the escape b introduce the addresses of blind carbon copy recipients these addresses will receive a copy of the letter but the mail header will not mention them as recipients To send out the above letter you can type mail null lt cmuser5 Here is the usual shell prompt i e the regular prompt given by the computer the reason it is called the shell prompt is that when the computer accepts commands it runs a program called shell and is not typed by the user null is the alias created above in the mailrc file and cmuser is the file containing the letter to be sent just described Instead of the above line you can type mail v
29. and 124 Step 2 Divide 124 into 422 the remainder is 50 We replace 422 with this remainder That is in place of 422 and 124 we will work with 124 and 50 Step 3 Divide 50 into 124 the remainder is 24 We replace 124 with this re mainder That is in place of 124 and 50 we will work with 50 and 24 Step 4 Divide 24 into 50 the remainder is 2 We replace 50 with this remainder That is in place of 50 and 24 we will work with 2 and 24 Step 5 Divide 2 into 24 the remainder is 0 The remainder being 0 we stop The greatest common divisor is the last nonzero remainder that is 2 Why does this procedure work Before we answer this question note that the procedure will always terminate In fact in each step we work with smaller numbers so in the end we must reach 0 as a remainder if no sooner then at the point when the last divisor is 1 To explain why the method works it is sufficient to note that each of the pairs we work with have the same greatest common divisor 546 422 422 124 124 50 50 24 24 2 2 0 We never actually worked with the last pair 2 and 0 since there is no reason to go on because it is clear that 2 0 2 It is easy to justify any of these equalities we will illustrate this with the discussion of the equality 422 124 124 50 54 IV APPLICATIONS OF PASCAL To see this note that 50 was obtained as the remainder when dividing 124 into 422 in fact 422 3 124
30. are called loop statements or loops The while statement is only one example of loop statements there are a num ber of other loop statements Loop statements are also called repetitive statements To understand what the above program does one must trace i e follow through its execution Rather than doing this by pencil and paper the computer can be used to do this All one needs to do to accomplish this is to insert writeln statements at key points in the program 1 program example5 input output 2 var i sum n integer 3 begin 4 write Type n n must be a positive integer 5 readin n 6 i 1 7 sum 0 Ta writeln line 7 sum sum 3 i i 2 8 while i lt n do 9 begin 9a writeln line 9 sum sum 3 i i 2 10 sum sum i 10a writeln line 10 sum sum 3 i i 2 11 i i tia writeln line 11 sum sum 3 i i 2 12 end 12a writeln line 12 sum sum 3 i i 2 13 write The sum of integers from 1 through 14 writeln n 1 equals sum 1 15 end We inserted lines 7a 9a 10a lla and 12a The purpose of numbering the lines this way is to not change the numbering of the other lines the line numbers are again not part of the file containing the program Note however that you will not be able to get the editor to display the line numbers this way the best you can do
31. by compressing the JPEG file picture jpg if it is included in a Web page using the HTML tag lt IMG gt described on p 26 Com pressing a JPEG file with gzip does usually result in a minor reduction of file size 10The letters ftp stand for File Transfer Protocol one of the ways to transfer files between different computers 11 The suffix tar stands for Tape Archive a Unix utility originally used for making tape backups However it has many other uses Documents with a complicated directory structure can be put into a single file using the tar command Such tar files often called tarballs often compressed with gzip form one of the favorite ways to store software on the Internet 34 Il THE WEB you click on the button OK in this window the window will go away The you can properly download the file by shift clicking on the link This time however Netscape will not spend time with downloading the file again it will take the file from its cache Command line control of Unix Netscape By typing netscape http linuxtoday com gt http www theregister co uk amp two Netscape windows will open one at each of the Web sites listed Note here that the sign in the first line is the prompt The backslash at the end of the first line is the Unix quote character Its role is the quote the end of line character the character making the display start at the beginning of the next line The end of line character usually created by p
32. const largestn 65535 OWAN A AF WN e e 12 CONDITIONAL STATEMENTS 51 11 var i sum n integer 12 begin 13 write Type n n must be a positive integer 14 readln n 15 if n gt largestn then 16 writeln n is too large 17 else 18 begin 19 i 1 20 sum 0 21 while i lt n do 22 begin 23 sum sum i 24 i i 1 25 end 26 write The sum of integers from 1 through 27 writeln n 1 equals sum 1 28 end 29 end This program is essentially identical to the earlier version except for two new fea tures First we included a comment in lines 2 9 a comment is any text placed between the braces and A comment does not affect the execution of a program in any way except that a comment acts as a separator the other separators namely spaces and end of line characters were discussed above thus one cannot place a comment inside the name of an identifier the same way one cannot place a space there at any place where spaces are allowed comments are also allowed and in fact one can use comments instead of spaces as separators The purpose of com ments is to document the program that is to explain its important features what it does how it does it how it may be changed who wrote it who changed it and when etc Often the person who wrote a program is no longer accessible or does not remember how the program works and someone else has to maintai
33. default name for a compiled program and is usually unwanted because if you wanted to keep the compiled program you would give it your own name rather than the default name see Section 8 The parentheses on lines 3 and for delimit the range of the disjunction of the patterns described by 0 these parentheses must be placed between single right quotes i e we have and The option user USER on line 5 means that only search for files owned by the USER which is the value of the shell variable USER naming the person who signed onto the computer so that you will not search for files owned by others The option type f means that you only look for files that are properly files and not directories Finally line 6 specifies what to do with the files that are found namely execute the rm command on them That is all the files that have been found will be removed the unaliasing of the rm command will make sure that you will not be asked about each file whether you really want to remove it The quoted semicolon indicates the end of the command named by the exec option 25 Source Scripts Shell aliases As we saw above if you want to run a sequence of commands repeatedly you can put them in a shell script and run the shell script instead There are however some notable things shell scripts cannot do namely they cannot change directories and they cannot change shell variables that is they can inside the scri
34. delimiters in TEX see TeX delimiters in Digital Equipment Corpora tion see DEC Diophantus 82 directory 8 creating 11 print working 10 root 10 sub 10 disjunction 71 displayed mathematical for mulas in TeX see TFX mathematical formulas in displayed div see Pascal key word div documenting Pascal pro grams see Pascal program documenting of domain name 126 DOS 37 dvi file see TX dvi file dvips 79 e mail see email echo 97 98 echo 110 ed 95 134 INDEX editing Unix commands see Unix commands editing with fc editor see Unix editor text 12 electronic mail see email Electronic Numerical Inte grator And Calculator see ENIAC email 86 96 reading 86 88 sending 88 96 sentmark Pascal program for see Pascal program for email sentmark shell escape in 87 shell script for writing see script shell for writing email tilde escape in 89 vs e mail Knuth s essay on Web 86 empty statement in Pascal see Pascal empty statement in end see Pascal key word end end of line character see character end of line endhead see TEX endhead ENIAC 40 enter key see key enter errors programming see pro gramming errors Euclid of Alexandria 53 Euclid s lemma 68 Euclidean algorithm 5 52 54 extended 59 60 implementing in Pascal of the 61 66 implementing in Pascal of the 54 56 ex 95 executable files locations for 96 exit 125 exponent in T X see TRX
35. example if one runs this script while Netscape is running without lines 3 5 and 14 commented out i e with the pound signs removed in addition to its killing Netscape one might get the following output the line numbers at the beginning are not part of the output we added them so that we can discuss the contents of this output 1 10522 pts 16 00 00 01 netscape commun 2 10532 pts 16 00 00 00 netscape commun 3 10522 4 10532 5 kill s 9 6 10522 7 10532 Lines 1 2 in this output are produced by line 3 of the script killns lines 3 5 are produced by line 3 4 by line 5 and lines 5 7 by lines 5 7 Consideration of this output will be helpful in understanding how the script works Line 2 of the script writes the first two lines of the output the command would write to the standard output screen but the standard output is redirected to the file junkkil10 so nothing gets written to the screen by line 2 of the script This output is similar to the output of the command ps x grep tempfile discussed above but some things are different Lines 1 and 2 in the output are each divided into four fields the fields are separated by one or more spaces What these fields mean can be seen from the headings produced by the command ps x discussed above see p 104 As seen from there first field is the process id PID the second one is TTY which is short for teletype but nowadays it refers to the 24 MORE SHELL SCRIPTS 107
36. found on every Unix computer In general computer languages can be compiled or they can be interpreted The former means that a program written in the given language called the source pro gram is first translated in to the computer s on language and a copy of this trans lated version is kept for later use the translated or compiled program is usually called the object program The latter means that no translated version of the pro gram is being kept The program is translated and executed at nearly the same time The advantage of compilation is that it has to be done only once and the object pro gram can be executed many times on the other hand interpreting a program is an easier task than compiling it The way line 1 specifies the shell to be used is interesting is the shell comment character and everything after is ignored by the shell Line 1 is a slight exception Here the fact that is immediately followed by the explanation point tells indicates that after a space character the shell to be used will follow the syntax of this first line has to be followed rigorously In line 2 the mail program is invoked in the way it was invoked in the preceding section The first argument of mail is works better The disadvantage of using the string cat gt dev null lt 1 is that when using the reply option on some systems to respond to emails sent by the above shell script the system tries to send a copy of the email
37. increment 47 induction mathematical 69 infinite descent method of 69 Information Theory 31 Infoworld Electric Web site of 5 input standard 57 input in Pascal see Pascal input in integer overflow in Pascal see Pascal integer overflow in integer type in Pascal see Pascal integer type in interface command line 100 graphical user 100 International Business Ma chines see IBM International Standards Or ganisation ISO Pascal Report 39 70 Internet 19 IP address 126 dynamic allocation of 126 static allocation of 126 ISO see International Stan dards Organisation ISO it see TEX it italics in T X see TFX ital ics in job control 124 126 jobs 125 JPEG file see file JPEG Julian calendar see calendar Julian Julius Caesar 76 justified right 46 Kernighan Brian W 107 key capitals lock 13 control 12 80 enter 9 13 escape 12 return 9 13 shift 80 kill 125 killing programs see pro gram terminating Knuth Donald Ervin 78 86 Korn shell see shell Korn kshrc file 121 INDEX languages programming see programming languages Latex see T X Latex LCM see least common mul tiple leap year 76 least common multiple 52 LF see line feed character line feed character 13 linear combination 59 Linux 5 6 information on the Web about 20 locations for executable files see executable files locations for lock file of Netscape see Netscape
38. indispensable for putting documents on the World Wide Web 1 Introduction to Using Unix Unix is a powerful operating system initially developed at ATT Bell Laboratories now Lucent Technologies Inc beginning around 1969 Today variants of Unix or Unix like operating systems run on many computers from supercomputers to workstations to personal computers They have different names for example the op erating system used on workstations made by Sun Microsystems is called Solaris an older but still very good operating system on these workstations is SunOS 4 x The operating system on IBM RS6000 workstations is AIX Many DEC Digital Equip ment Corporation computers use the Ultrix operating system Hewlett Packard workstations run the operating system called HP UX Linux A Unix like operating system called Linux is available for personal com puters and for some workstations It is a stable and powerful operating system and it can be obtained for free but installing it requires some skill You can read about it on the Internet at http www linuxworld com or at http www ssc com linux While there are many differences in these variants of Unix they all support the same basic features and for our purposes these differences will not be important For example things that you learn to do on Sun workstations you will be able to do usually without changes or only with minor changes on a personal computer running Linux Other free
39. key to add it at the beginning of the line Then press the return key to get the the next command line 3 Permission Codes In the interest of facilitating file sharing between users of similar category or interest users in Unix are placed into a number of groups You can belong to one or more groups of users You are able to give more privileges to a user that belongs to one of the same groups as you belong to than to other users We do not need to worry about user groups but this much is needed to understand the meaning of permission codes You may list files in the current directory with their permission codes by typing 1s 1 The answer you get may look like this total 8 rwWxr xr 1 jsmith cored 83 May 29 1991 edg arwetsscss 1 jsmith cored 440 May 22 17 27 euclid_new p SEW Ps f 1 jsmith cored O May 28 21 24 junk dr x x w 2 jsmith cored 1024 May 28 11 20 pascal rw r r x 1 jsmith cored 4698 May 25 18 44 sec5 tex jsmith in the middle of the line indicates that these files are owned by the user called jsmith and by the group called core5 the file names are given on the far right The 5Unix commands are often customizable and so fc may behave differently in particular another editor such as emacs may be invoked The editor to be used may be specified as the value of the shell variable FCEDIT 18 I UNIX letter d at the beginning of the line listing the file pascal indicates that this file is a directory the others a
40. letters amp d 2 3 5 will delete letters 2 3 5 and amp d 2 6 will delete letters 2 3 4 5 and 6 amp q will quit the mail program quitting and exiting is different If you exit the mail program by typing 88 V MISCELLANEA amp x then you can read all your letters again even if you have deleted some letters they will be undeleted If you quit the mail program the deleted letters will not be available again the letters that have not been saved or deleted will usually be put in a file called mbox in the user s home directory this action is dependent on how the system is set up in fact at least some accounts at the Atrium are not set up this way Sending email In your home directory there usually is a file called mailrc if there is not you should create one by using the vi text editor or some other editor you like If you type 1s you will not find this file listed the files whose names start with a period are hidden files but you can easily list them by typing 1s a In any case whether or not you have this file look at it or create it by typing vi mailrc You can add aliases for long mail addresses in this file that is you can add a line like this alias short user long email address at some university edu This will allow you to refer to the email address on the right by the abbreviated name alias short To send out email efficiently also add the line alias
41. lock file of see Netscape lock file of locked up window see win dow locked up log file in TeX see TFX log file logic propositional 69 logical operators in Pascal see Pascal operators in log ical Login file 97 login name 7 loop nested 71 loop in Pascal see Pascal loop in lpr 80 header page suppressing 80 ls 9 F option of 9 a option of 21 d option of 12 1 option of 17 Lucent Technologies 6 lynx 26 137 machine language 36 magnification in TEX see TEX magnification in magstep see TEX magstep mail alias see alias mail mailrc file 88 maintenance of programs see program maintenance of man 9 manual on line 9 mathematical formulas in TEX see TFX mathemati cal formulas in mathematical induction see induction mathematical mathematical italics in Tex see TpX italics mathemati cal in mathematical typesetting see typesetting mathematical McGough Nancy 5 metacharacter in vi 14 escaping 14 method of infinite descent see infinite descent method of Microsoft Corporation 7 finding of facts in the antitrust case 7 Mindspring Internet service provider 127 129 mistake in TFX files see TEX mistake in files mkdir 11 mod see Pascal key word mod more 105 mouse 19 20 Mozilla 35 Mozzochi Charles Jeffrey 24 27 mv 11 negation 70 INDEX nested loops see loop nested NetBSD 6 Netscape 19 22 bookmarks 20 cache of 21 command line
42. marks sentmark gt gt 1 4 date tha lt b d hr ZZ LY gt gt 1 23 SHELL SCRIPTS 91 chmod u x email We will say a few words about where this file should be located for the moment it can reside in the directory where the email letters to be sent out are located there are things that can go wrong here we will discuss the execution search path below to indicate how to fix possible problems To send out the email letter in the file cmuserd you will be able to type email cmuser5 but just not yet One more thing will have to be taken care of as you will see Next we will explain how the shell script email works In line 1 it is specified that the version of shell contained in the file bin sh is to be used In Unix there are a number of command interpreters called shells The one in bin sh is called the Bourne shell and it is mainly used for writing shell scripts since there are newer shells that are preferred for interpreting commands entered on the command line Such newer shell are the C shell at bin csh or its enhancement at bin tcsh the Korn shell at bin ksh and the Bourne again shell at bin bash Not all Unix computers will have all these shells C shell is used mainly on the command line and is not recommended for shell scripts while the Korn shell and the Bourne again shell are used both on the command line and in shell script There are yet other shells that we will not mention here not all shells can be
43. not appear in the typeset text Delimiters have many uses here they indicate that the effect of the control sequence smc applies only between these delimiters the meaning of this control sequence is typeset everything that follows in small capital typeface Line 16 is a blank line a blank line starts a new paragraph so the text that begins on line 17 starts a new paragraph Single quotes are obtained by typing and while double quotes are obtained by typing and i e by typing two 84 V MISCELLANEA single quotes rather than using the double quote key on the keyboard thus the text on lines 17 22 will be typeset within double quotes Mathematical formulas are enclosed within dollar signs On line 17 n gt 2 is typeset as n gt 2 a is typeset as a Note that mathematical symbols have a different type face from regular text the type face is called mathematical italics and it is a little different from regular italics i e slanted typeface the word slanted however should not be used here since slanted is a little different from italics this is slanted and this is italics Mathematical formulas that are between double dollar signs will be displayed in the middle of the line Thus the formula a n b n c n is printed as a b c Note that we put the formula in line 19 in a separate line by itself however this did not make any difference and the typeset version would have been the same e
44. null cat gt dev null This line has to be typed exactly as is including the spaces The character vertical line is called pipe in Unix and is usually found on the same key as backslash 1 For letters to be sent create a directory called mail_sent and write all letters to be sent out in this directory A typical letter would be a file called cmuser5 the 5th letter sent to cmuser with the following content created by an editor such as vi 15The casual user does need to know how this alias works pipes are described in p 105 For those with some knowledge of Unix and Unix mail here is an explanation An alias is needed that will cause no action as the on line manual of mail indicates pipes are allowed as mail aliases Here the effect of the pipe is to cat the content of the file to be mailed into dev null doing this may waste a little computer time but has no other perceptible effect In Linux the alias works just as well in fact it works even better on Suns it does not work properly It will send out the letter but it will also complain null not a group where null is the alias for It will then save the letter into a file called dead letter usually in the user s home directory this totally defeats the purpose of the above alias so on Suns the mail alias is not usable The on line manual for aliases 5 gives a partial answer to this difference in behavior between Linux and the Sun s operating sy
45. null lt cmuser5 where the option v is the verbose option in this case the computer will write a detailed log on the screen as to what happened to the email you just sent it might take a few seconds before this log appears since it might take some time before the receiving computer is contacted Actually in Linux one must type mail I null lt cmuser5 or 90 V MISCELLANEA mail vI null lt cmuser5 instead of the above lines The option I forces the so called interactive mode Actually this term is misleading since mail there is nothing interactive about the way we are sending email the only significance of interactive mode is that in Linux interactive mode is needed for the mail program to accept the tilde escapes described above this may not be true for all version of Linux check the online manual pages for mail to find out To explain these commands note that in these examples the mail command considers the argument called nu11 the address where the mail is to be sent and the argument cmuser5 the letter to be sent out Both arguments are required though there are also other ways to use the mail program However the address null basically tells the mail program to send the letter to no one while the letter cmuser5 to be sent out contains information about the disposition of the mail where to send it what to send that is only parts of the file not the tilde escapes and the comment The letters that w
46. num2 1 is sum 1 then the end of line character is not printed The effect of this is that after finishing the program the prompt for entering a new command appears on the same line as the printout of the program Assuming that the prompt is the printout will now look like this The sum of 15 and 12 is 27 as we explained is not part of the printout it is the prompt which would normally be printed on the next line in actual fact the prompt you get will usually be different Lines 7 and 8 can be replaced with a single writeln statement 10 MORE ON PASCAL 43 writeln The sum of numi 1 and num2 1 is sum 1 That is we listed all items to be printed in a single writeln statement since putting all items in a single line would have made the line too long we broke up the line after the third item The next program is a slightly modified version of the one above 1 program example4 input output 2 var numi num2 sum integer 3 begin 4 write Enter the first number 5 readin num1 6 write Enter the second number 7 readin num2 8 sum numi num2 9 write The sum of numi 1 and 10 writeln num2 1 is sum 1 11 end The word input in the program heading line one indicates that the program will read from the input file which at present is the window in which you are working The meaning of the readin statement in line 5 is that w
47. occurrences of the text there is to there are in line 12 The command 24 78 7 u will add two spaces at the beginning of lines 4 7 Here the symbol caret indicates the beginning of the line and the symbol indicates the space character on the screen the space character is not shown except that it occupies a space between two words say but it is customary to use the symbol to emphasize the presence of a space character The character is called a metacharacter in vi This is because the character is used to denote something other i e the beginning of the line then the character itself Typing 4 78 will add a semicolon at the end of each of the lines 4 7 This is because the metachar acter denotes the end of the line in vi You can escape metacharacters by quoting them with the aid of the Unix quote character backslash That is 4s g 2 THE VI TEXT EDITOR 15 will replace all occurrences of the character with the character in line for by placing in front the character no longer acts as a metacharacter Notice that the character in the replacement text in this example does not need to be escaped in the replacement text never acts as a metacharacter it would not make much sense to refer to the end of the line in the replacement text The command 78 will replace the first occurrence of the character with a caret The command 4 7t19 will copy lines 4 7 after line
48. replace the character at the current cursor position type r and then the new character For example rx replaces the current character with x typing rr will replace it with r Finally typing r LF replaces it with the line feed character here LF stands for the line feed character obtained when pressing the enter key also called return key on the keyboard That is if you type r LF over a space character the result is the break up of the line into two lines at the given location To join two lines type J over the first one of them To change a word while in command mode type cw with the cursor being on the first character of the word The word will be deleted and the editor will change to insert mode that is the text you type at the keyboard will be added to the file you would usually type a replacement word and then go back to command mode by pressing the escape key Typing D will delete the rest of the current line the part to the right of the current cursor position while typing C will allow you to change the rest of the current line You can use numbers with the some of the above commands Typing 3dd deletes three lines typing 4x deletes four characters Typing 2dw deletes two words typing d2w does the same the latter is perhaps the more logical order since you can read it as saying delete two words typing 2cw or c2w will allow you to change two words To go into insert mode before the current cursor position t
49. see Pascal program truth ta bles for INDEX tt see TEX tt Turing Alan 36 type text in Pascal 58 type in Pascal see Pascal type in typesetting mathematical 78 85 typesetting TEX files see TEX typesetting files in typewriter font in TFX see TEX typewriter font in Ultrix 6 uncomment 65 underscore _ 9 84 Unices plural of Unix 111 Uniform Resource Identi fier see HTML Uniform Resource Identifier in Uniform Resource Locator see HTML Uniform Re source Locator in unique file names see file name unique in shell scripts universal machine 36 Unix 5 18 commands breaking up 34 editing with fc 16 compared to Windows NT 7 directory tree and TFX see TEX Unix directory tree and editor ed see ed ex see ex vi see vi process 103 quote character back slash 14 34 URI see HTML Uniform Resource Identifier in INDEX URL see HTML Uniform Resource Locator in user groups 17 v Neumann see von Neu mann John var see Pascal key word var variable of type text in Pascal 58 propositional 69 variable in Pascal see Pascal variable in variable in shell see shell variable vi 6 12 15 command mode 12 command line mode 14 cursor movement in 12 insert mode 12 13 line numbers in 14 quitting 15 view 127 von Neumann architecture 40 von Neumann John 40 vt100 128 Web see World Wide Web World Wide see World Wide Web Web page how to build a 22 29
50. shell script can save typing time when compiling Pascal programs 1 bin sh 2 pe s 1 p o 1 comp gt errors 3 cat errors Calling this script compile one can compile a Pascal program called example pc by typing compile example This will produce an executable file example comp provided the compilation is suc cessful and the possible errors that occur during the compilation are first written in the file called errors and then written on the screen There are clear advantages of writing the errors into a file since they are preserved for later viewing whereas the text displayed on the screen is not Putting files on the Web Suppose you worked on a Pascal program called say example p and you want to display it on your Web page You can do this by copying it into your public_html directory and setting its permission code to 644 see Section 5 p 23 Rather than doing this manually you can do this by the following shell script called say putonweb 1 bin sh 2 cp f 1 HOME public_html 3 cd HOME public_html 4 chmod 644 1 To use this shell script to put the Pascal program example p on the Web you need to change to the directory where this file is located and then type putonweb example p There are two things to note about this shell script If there is already a file called example p in the directory public_html the above command will destroy it that is replace it with the new version of example p this is b
51. some setups will log you out automatically when you exit OpenWindows but other setups will not and you can never rely on being logged out automatically Netscape and the World Wide Web There are certain applications that you will only be able to use in the OpenWindows environment because these applications rely on X Windows resources Notably among these is Netscape which will allow you to look at information put on public view on computers all over the world To open Netscape type netscape amp 20 Il THE WEB The effect of typing the symbol amp ampersand at the end of the line is to run Netscape in the background What this means in practical terms is that after Netscape is started the window in which the above line was typed is immediately available for other use such as editing ordinary files If one types netscape i e if one omits the symbol amp at the end of the line Netscape will run in the foreground and the window in which this line was typed will be unavailable until Netscape is closed other windows will however be available After learning how to use the mouse in general it is fairly easy to learn how to use Netscape After starting Netscape one can visit the Brooklyn College Web site by first clicking with the left mouse button on the word File in the Netscape windows this will open a small window with a number of choices By clicking with the left mouse button on the phrase Open Location among these ch
52. that the program will look nice to the human reader 18 THE FUNDAMENTAL THEOREM OF ARITHMETIC 67 3 If one follows the hint at the end of the preceding problem and one enters 546 and 422 in this order the equations representing each of the numbers 546 422 124 50 24 and 2 as a linear combination of 422 and 546 will be printed However if one enters the same numbers in the order 422 and 546 the equation representing 546 will not be printed How can this situation be corrected Hint The easiest way is to insert a conditional statement in the program after the input statements so that if necessary the numbers are interchanged to make the variable a represent the larger number and the variable b the smaller number This can be done the same way as in Problem 2 of 14 see p 56 Explain why this idea works and write the program 4 If the program written in Problem 3 is run with the inputs 546 and 422 there is still a minor problem The first two equations printed look as follows 546 546 1 422 0 422 546 0 422 1 The parentheses in these lines are not needed and the output would look better if they were not printed Explain why the parentheses are printed and modify the program in such a way that these parentheses are not printed 18 The Fundamental Theorem of Arithmetic An integer is a prime if it is greater than one and its only divisors are one and itself The first few primes are 2 3 5 7 11 13 17 19 23 29 31
53. the command fc This will invoke the editor vi with the mistyped command as the content of a 3 PERMISSION CODES 17 temporary file being edited If you make corrections in this file using the editing commands of vi discussed above and quit the editor the corrected command will be executed When typing a command and you realize that the command you typed is incor rect you may rescue the situation by adding the pound sign at the beginning of the line this will prevent the command from executing For example the command cd vi_experiment will do nothing Then you may type fc to correct the mistakes in the command How to add the pound sign at the beginning of the current command line depends on the version of Unix shell you use If you use Korn shell the shell used at the Atrium after noticing your mistake in the command you press escape then you press caret to get to the beginning of the line This works the same way as in vi Then as in vi you press i to go into insert mode then you press the pound key to add the latter character at the beginning of the line Then press the return key to get to the next command line as we mentioned the command just edited will do nothing since it starts with the character In the bash shell which is common in Linux after noticing your mistake you press Ctl a while holding down the control key press a This gets you to the beginning of the line Then press the pound
54. time error but we run into a problem when running the program This run time error may have more or less serious consequences with some compilers the consequence is simply that the program will not perform correctly and indicates this with a harmless message On 16 THE GREATEST COMMON DIVISOR AS A LINEAR COMBINATION 59 the Atrium Sun computers when running the program the way described we get the following message Trace BPT trap coredump This is a message that you will have to deal with You probably will not want to study the meaning of Pascal error messages at this point so we will not discuss what the message Trace BPT means The meaning of the word coredump is however important The computer put the entire content of the memory related to the running of the program into a file called core so that the cause of the error could be analyzed This may be important when trying to find the cause of the error however analyzing the file core requires some knowledge of programming that is beyond the scope of this book What is important for now is that the file core is quite large usually over 8 megabytes and unless you are prepared to use it for analyzing the cause of the error you should remove it as soon as possible by typing rm core to avoid wasting memory space Returning to the description of the above program as originally presented i e with read rather than read1n on lines 6 and 7 lines 8 13 work the s
55. tmp junknetscape lt lt heremark 2 gt dev null 39 Oa 40 netscape remote openURL 41 new window AD 43 1r 1 44 2 1j 45 2s 46 2s 2C g AT 2s h2C 48 2s 49 2s g 50 1 33 51 w 52 q 53 heremark 54 fi 55 HOME tmp junknetscape amp 56 touch HOME tmp junknetscape 57 rm f HOME tmp junknetscape gt dev null We will not go through in detail as to how much this script works because it has a lot of similarities with the preceding script The main point that is new here is to deal with the error handling of a here document using the editor ed We recall that this problem which makes ed exit prematurely if it receives a substitute command that never finds a match to substitute caused us to use several here documents in the preceding script Here line 26 in the above script inside a here document substitutes each comma in the second line of the file junknetscape with the string 2C we recall that 2C is the hexadecimal ascii code of the comma see p 116 above This substitution however would fail if the line in question contains no comma Therefore line 26 adds a comma to the line as its last character and line 28 removes the string 2C resulting from the substitution of this comma In a similar manner line 29 adds a space as the initial character to line 2 of the file being edited and line 30 removes all spaces from this line line 29 guarantees that the substitution in
56. to enclose mathematical formulas In line 57 the control sequence centerline will center the text between the delimiters and The control sequence tt indicates that this text should be set in typewriter font that is the letters look like they were typed on a typewriter rather than printed The text to be centered should be a separate paragraph this is why lines 50 and 53 were left blank The control sequence bye in line 54 signifies the end of the tex file There is much more to know about T X and in order to learn it you need to consult books written about it To find out more you can look up T X related material at the Web site of the T X Users Group http www tug org interest html An introduction to Latex can be found at http riceinfo rice edu Computer Documents Classes Unix class class html We had to break the line here but note that there are no line breaks or spaces in the above address TeX and the Unix directory tree We mentioned above the meaning of the input somefile statement instead of proceeding with the working on the present file the content of the file called somefile tex is going to be processed In place of taking a simple file located in the present directory most up to date Unix installations of TeX can refer to anywhere in the Unix directory tree For example one can write the following line input texinputs mytex This takes inputs from the file mytex tex located in the subdire
57. to make unique filenames in Linux one can do this by using the mktemp program See the online manual pages for mktemp in Linux to see why this is safer than using the process id In Solaris mktemp is available only as a C library function 104 V MISCELLANEA 10 q 11 12 junknetscape 13 rm f junknetscape This identical to the script above except that we used the filename junknetscape instead of junknetscape Killing Netscape On occasion one encounters a Web site that was not prepared to Netscape s liking and it causes Netscape to crash in which case the Netscape window suddenly disappears without any explanation or freeze in which case the Netscape window stays but no amount of clicking can make it do anything and Netscape becomes totally nonresponsive Even if the Netscape window disappears the Netscape program or process as it is called is probably still around As we mentioned above in Unix the instance of a running program is called a process seep 103 To find out what processes are running one can use the command ps with various options For example typing ps x where the option x explained in the Unix online manual pages as selects all processes might produce the following list PID TTY TIME CMD 1 00 00 04 init 27 00 00 35 kflushd 425 00 00 00 nfsd 426 7 00 00 00 nfsd 427 00 00 00 nfsd 644 tty4 00 00 00 mingetty 23258 7 00 00 00 xterm 6421 pts 13 00 00 39 netscape commu
58. touch HOME tmp junknetscape if test z ps x grep netscape grep v grep awk print 1 cat 2 gt dev null then rm rf HOME netscape cache rm rf HOME netscape lock ed HOME tmp junknetscape lt lt heremark 2 gt dev null Oa netscape NNNNRPRPRPRP BB WNrFrFrDOOAOAN DO ir 1 2 j W q heremark else ed HOME tmp junknetscape lt lt heremark 2 gt dev null Oa netscape remote openURL new window WWWWWNHNNNN ND BPwWNRrFOUOAN DOF 24 MORE SHELL SCRIPTS 115 35 ir 1 36 2 1j 37 w 38 q 39 heremark 40 fi 41 ed HOME tmp junknetscape lt lt heremark 2 gt dev null 42 2s 2C g 43 w 44 q 45 heremark 46 ed HOME tmp junknetscape lt lt heremark 2 gt dev null 47 2s g 48 w 49 q 50 heremark 51 ed HOME tmp junknetscape lt lt heremark 2 gt dev null 52 1 j 53 w 54 q 55 heremark 56 HOME tmp junknetscape amp 57 touch HOME tmp junknetscape 58 rm f HOME tmp junknetscape gt dev null Next we will explain how this script works In line 2 it is tested if the first and only argument of the script is s this is done by the test command which in the form test string string compares if the two strings string and string are identical The problems is that this cannot be used directly to compare the string s to another string since the command test with the option s has a special meaning Namely the command test s file
59. will be copied into this directory as a new subdirectory Wildcards in filenames The asterisk in filenames is called a wildcard since it matches any string of characters For example the command ls d p s might produce the reply papers picture ps proposal purchases that is files or directories with names that begin with p and end with s The explanation for the option d if a file in question is a directory then this option ensures that only the name of the directory is given without this option after the name of the directory all the files in the given directory would also be listed if the name of the directory matches the pattern described in the argument of the 1s command in the present case the argument is p s that is the string given after the command 2 The vi Text Editor Text editors enable one to create text files Unix has a number of text editors a widely used among them is called vi for visual You can start up vi by typing vi filename Before doing this make sure that you are in the directory where you want to work in The whole screen or window if you are using a window system see below will change and you will be in vi command mode In order to be able to enter text you should type 7 and then you can enter text by using the keyboard as on a normal type writer When you can enter text the editor is said to be in vi insert mode If you have entered a sufficient amount of text or you feel you ne
60. window You might then forget about the hidden login window and a later user of the public computer may have access to your private account Connecting to a friends Unix machine The remote connection capabilities of Unix may allow you to be connected to a machine of your friend at a different location provided both of you are connected to the Internet For example assume your friend using a machine running Red Hat Linux has an account with the Internet service provider Mindspring As a first step she connects to her Internet service provider Mindspring using the protocol ppp As the second step she emails you her local IP address In the discussion above we mentioned that this is written in the file var log messages and the simplest way for her to send it to you is by emailing the whole file to you provided she trusts you with the information in this file otherwise she needs to find her local IP address in this file and only email that to you Since the file var log messages is not readable and cannot be emailed by a regular user she first must become a superuser to do this Having done so she can email the file var log messages to you by typing mail v your_ematl_address lt var log messages Here indicates the superuser prompt as mentioned above Upon learning the IP address of your friend you can log into her computer by typing rsh 1 login_name IP_address Here login name is your login name on her machine unless you ar
61. 2 Il THE WEB arbitrary binary files frequently occurring bit sequences can be represented by a shorter code than rare bit sequences The compression of images is based on a different idea A picture is represented in a computer by storing all the pizels picture elements i e the brightness and color information for each point of the picture Since nearby pixels usually differ very little in a human face nearby points are usually of nearly the same color for example instead of storing all the pixel values for most pixels it is more efficient to store how it differs from a nearby pixel that is stored in full There are various mathematical algorithms for compressing images The require ments for image compression are less stringent than for compressing a file containing English text The compression of a text file should be lossless that is from the compressed file one must be able to reproduce the original text exactly For image compression it is often permissible to be lossy it may not matter if the original image data cannot be reconstructed if the human eye cannot tell the difference be tween the original image and the image reconstructed from compressed data GIF is a lossless image compression scheme while JPEG is a lossy one The advantage of a lossy image compression scheme is that usually greater compression can be achieved Compressed Web pages The file compression program gzip and its sister gunzip used for uncompressing
62. 29 temporary files directory for see tmp directory for tempo rary files terminal type 128 vt100 see vt100 terminating programs see program terminating test Unix command 112 z option of 112 TEX 5 78 85 in see TpX asterisk in in 85 sign in see TX per cent sign in in 85 AMS Preprint Style 83 AMS TEX 83 asterisk in 81 bf 84 bold face in 84 bye 78 85 centering lines in 85 centerline 85 comment in 85 control sequence in 78 control sequence TeX in 78 delimiters in 83 dvi file 79 endhead 83 exponent in 84 head 83 it 84 italics mathematical in 84 italics in 84 Latex 83 log file 79 142 magnification in 83 magstep 83 mathematical formulas in 84 mathematical formulas in displayed 84 mistake in files 80 par 84 paragraph in new 84 percent sign in 85 Plain 83 previewing 79 quotes in 83 s1 84 slanted in 84 smc 83 subscript in 84 superscript in 84 tt 85 typesetting files in 78 typewriter font in 85 Unix directory tree and 85 Users Group 85 Web site of 85 Web sites about 85 xzdvi previewer 79 TeX see TX control se quence TeX in text file see file text text file type in Pascal see Pascal key word text The Register see Register The tilde escape in email see email tilde escape in tmp directory for temporary files 112 touch 23 tracing Pascal programs see Pascal program tracing of truth tables in Pascal
63. 5 each contain a statement The statement on line 4 is called an assignment What it does is to give i e assign the value 15 to the variable called num The assignment symbol i e a colon followed by an equation sign can be read as is to be replaced with i e the current value of num is to be replaced with the value of the expression on the right hand side The symbol must be distinguished from the equation sign which is also used in Pascal programs see later We already met the writeln statement Here the statement writes two items to the output file the screen The first item is quoted and is written exactly as indicated 10 MORE ON PASCAL 41 between the single quotation marks both of them right quotes The second item separated from the first item by a comma to be printed out is the value of the variable num In the string num 1 the 1 after the colon indicates that the minimum width of the space used for printing the variable should be 1 characters more space is used if it is needed to print this value The number indicating the width can be omitted That is instead of line 5 one can write the line writeln The number is num but in this case a default number i e a number decided upon by the computer or rather by the compiler will be used as width and you may not like this default If for example the default is 5 the printout would look like this The number is 15 Here three spaces are added
64. 50 This equation shows that any common divisor of 124 and 50 is also a divisor of 422 if one writes this equation as 50 422 3 124 then one can see that any common divisor 422 and 124 is also a divisor of 50 Therefore the common divisors of the numbers 422 and 124 are the same as the common divisors of the numbers 124 and 50 i e the greatest common divisor of 422 and 124 is the same as the greatest common divisor of 124 and 50 14 Implementing the Euclidean Algorithm in Pascal To describe more how the greatest common divisor of 422 and 546 was determined in each step write a for the smaller number and b for the larger number That is in Step 1 a 422 b 546 in Step 2 a 124 b 422 in Step 3 a 50 b 124 in Step 4 a 24 b 50 in Step 5 a 2 b 24 in Step 6 a 0 b 2 Earlier we only had five steps here we included a sixth step to indicate that in the last step we had to determine the greatest common divisor 2 0 It is easy to describe how the new values of a and b are obtained in each step Consider for example Step 2 The current values of a and b in this step are given as a 124 and b 422 Denote by anew and bnew the new values of a and b i e the values of a and b that will be used in the next step i e in Step 3 We have anew 50 and bnew 124 It is easy to write the formulas that calculate the new values Write z mod y for the remainder when y is divided into x in fact this is the n
65. By pressing the space bar on the keyboard you can see the next windowful By pressing the return key your view of the file will advance by a single line By typing b you can go back by one windowful this may not work on older systems Once you get to the end of file you get back to the Unix command line You can get back to the command line earlier by typing q The symbol we used the more command above is called a pipe Its meaning is to take the output of the command on the left and use it as the input on the right more precisely the standard output see pp 57 and 102 of the first command is taken as the argument input file of the second command That is the command ps x more is equivalent to the two commands ps x gt tempfile more tempfile except that the version with the pipe does not leave the temporary file called tempfile behind Here in the first line the greater than sign gt redirects the standard output into the file tempfile and in the second line more uses this file as its argument The command grep netscape tempfile writes those line of the file tempfile to the screen that contain the word netscape Thus the command ps x grep tempfile will give only part of the output of the command ps x described above that is we will get only those lines of the output that contain the word netscape 6421 pts 13 00 00 39 netscape commun 6431 pts 13 00 00 00 netscape commun After these preliminaries we w
66. CII refers to the way these files are encoded ASCII or ASCII pronounced ask ee is an abbreviation of American Standard Code for In formation Interchange and describes the most wide spread way computers store letters numbers punctuation marks and control characters If you are not sure what kind of file is a file called myfile is you can find this out by typing file myfile Note here that at the beginning of the line is the prompt given by the computer The computer may give a reply such as myfile ascii text 2 Atrium in these notes refers to the Atrium Computer Laboratory at Brooklyn College see http acc6 its brooklyn cuny edu 1 INTRODUCTION TO USING UNIX 9 Or you may get a reply such as myfile ascii directory Directories are special kind of files that are used to organize the information on the computer In order to organize the files you may have related files are grouped together into a single unit called directory they work much the same way as in a paper filing system you put related documents in the same folder in fact Macintosh computers use the name folder rather than directory To list the contents of i e the files grouped together in a directory type 1s 1s stands for list but you should always type ls and not list the latter is only the origin of the name of the command and it is not recognized by the computer The reply you receive may look like edg euclid_new p junk j
67. DAAN ODOAKFE WBN HF OO lt HTML gt lt HEAD gt lt TITLE gt Attila Mate s Home Page lt TITLE gt lt HEAD gt lt BODY gt lt BR gt lt HR gt lt BR gt lt CENTER gt lt H1i gt Attila M amp aacute t amp eacute s Home Page lt H1 gt lt CENTER gt lt BR gt lt HR gt lt BR gt lt IMG ALIGN LEFT BORDER 0 SRC Matecsm gif ALT Picture HSPACE 25 gt lt the ALT attribute defines an alternative text to the picture used by text browsers gt lt ADDRESS gt lt BR gt Attila M amp aacute t amp eacute lt BR gt Department of Mathematics lt BR gt lt A HREF http www brooklyn cuny edu gt Brooklyn College lt A gt lt BR gt 2900 Bedford Avenue lt BR gt Brooklyn lt A gt NY 11210 2889 lt BR gt USA lt BR gt lt A HREF mailto mate sci brooklyn cuny edu gt e mail mate sci brooklyn cuny edu lt A gt lt BR gt office phone 718 951 5246 lt BR gt lt BR gt Photograph by C J Mozzochi lt ADDRESS gt lt BR CLEAR LEFT gt lt The above line moves the text position vertically down to the next unobstructed left margin gt lt BR gt lt HR gt lt BR gt amp 160 amp 160 lt This is the space character to create indentation gt To see my letter sent to the London Sunday Times in response to a negative article about Linux lt A HREF http www ssc com linux suntimes rebut htm1 6 HYPERTEXT MARKUP LANGUAGE 25 47 gt click here lt A gt 48 To m
68. INTRODUCTION TO OPEN COMPUTING ATTILA MATE Brooklyn College of the City University of New York July 1997 Last Revised January 2003 1997 2003 by Attila Mat Typeset by AMS T X TABLE OF CONTENTS TABLE OF CONTENTS Preface Chapter I Unix I 2 3 Introduction to Using Unix The vi Text Editor Permission Codes Chapter II The Web 4 5 6 ts X Windows and Netscape Starting to Build Your Own Web Page Hypertext Markup Language Empowering Netscape Chapter III Pascal 8 9 10 11 12 Introduction to Pascal Simple Pascal Programs More on Pascal Loops Conditional Statements Chapter IV Applications of Pascal 13 14 15 16 17 18 19 20 The Euclidean Algorithm Implementing the Euclidean Algorithm in Pascal File Handling in Pascal Representing the Greatest Common Divisor as a Linear Com bination Pascal Program for Finding the Representation the Greatest Common Divisor as a Linear Combination The Fundamental Theorem of Arithmetic Truth Tables Day of the Week Chapter V Miscellanea 21 22 23 24 25 26 27 28 Mathematical Typesetting Electronic Mail Shell Scripts More Shell Scripts Source Scripts Job Control Remote Access Solution to Problem 1 in Section 16 Index 12 17 19 19 22 23 29 36 36 40 41 44 48 52 52 54 57 59 61 67 69 72 78 78 86 90 100 121 124 126 130 131 PREFACE 5 PREFACE
69. In Pascal these equations can be written as follows a0 a bO b 64 IV APPLICATIONS OF PASCAL x 0 po cy er aly x1 1 yl 0 In the equations of first line we interchanged the sides i e we assigned the value of the variable a to ag and b to bo rather than the value of ap to a and bo to b as one would expect on the basis of the equations above The only reason for this is that we would like to keep the similarity between the original program for the Euclidean algorithm and the program being designed at present That is the values entered at the keyboard will first be read into a and b and then these values be also assigned to ag and bo rather than reading these values first into ag and b and then assigning them to a and b Putting all these together a preliminary version of the program can now be written as follows 1 program euclid input output 2 The greatest common divisor d of two positive 3 integers a and b entered at the keyboard is 4 calculated and is represented in the form d ax tby 5 where x and y are integers 6 vara b a0 bO q x y x1 y1 temp 7 tempx tempy integer 8 begin 9 write Type a a must be a positive integer 10 readln a 11 write Type b b must be a positive integer 12 readln b 13 a0 a bO b 14 XS Op oy i i 15 xt Lyd 0 16 while a lt gt 0 do 17 begin 18 temp a 19 q b div a 20 a b mod a 21 b temp
70. John Backus The programming language Pascal named after the seventeenth century French mathematician Blaise Pascal was developed in the late 1960 s under the leadership of Niklaus Wirth In the early 1980s it was one of the most popular programming languages and it is still one of the most elegant languages Recently its popularity has given way to the language called C While Pascal is easier to learn and mistakes in Pascal programs are usually easier to find C is closely associated with the Unix operating system It is unlikely however that the world will soon agree on a single programming language For example FORTRAN is still important since it handles large numerical calculations more efficiently than C or Pascal Then there are many computer languages used in specialized areas for example we met HTML before see Section 6 on p 23 and we are going to meet the mathematical typesetting language T X see Section 21 on p 78 Whatever the future of Pascal after learning to program in Pascal it is much easier to learn other programming languages 8 INTRODUCTION TO PASCAL 37 One of the simplest Pascal program is the following 1 program hello output 2 begin 3 writeln Hello world 4 end The numbers on the left are not part of the program they are line numbers that allow us to more easily explain what this program does When run i e executed or made to do its work the only visible action of this program wi
71. Manual and Report third edition Springer Verlag New York Berlin 1985 12 3 4 12 3 5 on pp 198 199 19 TRUTH TABLES 71 3 begin 4 writeln A B result 5 writeln 6 a true 7 b true 8 repeat 9 repeat 10 result a and b 11 writeln a 1 gt b 1 gt result 1 12 b not b 13 until b 14 a nota 15 until a 16 end The printout looks as like this 21 A B result 22 23 T T T 24 T F F 25 F T F 26 F F F The above program contains two nested repeat loops i e one loop is inside the other loop The outside loop in lines 7 15 is entered with a true and in the same way as in the first program this loop is executed twice first with a true and the second time with a false Similarly for each execution of the outside loop the inside loop on lines 9 13 is executed twice first with b true and then with b false In line 10 the conjunction of a and b is calculated the operator and denotes logical conjunction and in line 11 one line of the truth table is printed One can use the same idea to print truth tables containing more than two vari ables The following program prints out the truth table of the formula AAb V C where A stands for conjunction V for disjunction and for negation the operator for disjunction in Pascal is or 1 program example output 2 var a b c result boolean 3 begin 4 write A B 5 writeln C result 6 writeln
72. Netscape to view PostScript files when using clicking on link to such a file a separate ghostview window will open to display the document This window can be closed simply by typing a letter q anywhere in the main part of the window Enabling Netscape for viewing PostScript may have a side effect that is easy to deal with When clicking on a link representing a PostScript file in a Web page Netscape tries to download the file unless Netscape is enabled to view PostScript files as described above If you enabled Netscape to do this and you still want to download the file rather than view it you need to shift click on the link that is depress the Shift key on the keyboard and then click on the link This will prevent Netscape from viewing the file If you do not know whether after clicking on a link Netscape would display the item or download the file it is alway safe to shift click to make sure that Netscape will download it rather than display it Data Compression The idea of data compression goes back to Claude E Shan non the founder of Information Theory who came up with the idea in the late 1940s In the ASCII code a letter is represented by an eight bit code In everyday English the letter e occurs significantly more often than the letter z for this reason the number of bits used to represent an English text can be lowered if the letter e is described by a shorter code than the letter the letter x This idea can be generalized 3
73. S A LINEAR COMBINATION 63 In Pascal b div a denotes the quotient when a is divided into b Thus we will write q b div a to calculate q in the equation b aq r Thus the rest of the update equations can be written as q bdiva Ti new T qT1 Yl new Y q1 In order to accomplish this update in Pascal we need to use certain temporary vari ables even in the original program performing the Euclidean algorithm we needed a temporary variable We write 1 while a lt gt 0 do 2 begin 3 temp a 4 q b div a 5 a b mod a 6 b temp 7 tempx x1 tempy y1 8 xl x q x1 yl y q y1 9 x tempx y tempy 10 end We surrounded the whole passage with a loop starting in line 1 and ending in line 10 in the same way as the original program for the Euclidean algorithm the passage in lines 3 9 has to be repeated as long as a 0 in fact lines 3 5 and 7 are the same as the lines in the loop of the Euclidean algorithm To start off this loop consider the initial equations in the method representing the greatest common divisor as a linear combination 546 422 0 546 1 422 422 1 546 0 This is the place in the algorithm when we use the first two equations to derive the third equation At this point the above equations correspond to the algebraic equations b aox boy a agz boy That is our initial equations are a ao b bo x 0 y 1 vy l yi 0
74. To quit being superuser you need to type exit Remote login and telnet Instead of rsh one can use remote login to similar effect rlogin 1 login name machinename its brooklyn cuny edu Telnet works essentially the same way but uses a different protocol to connect to a remote machine telnet machinename its brooklyn cuny edu Specifying terminal type When remotely connecting from a Unix machine to another Unix machine the connection is usually established smoothly without needing additional intervention When connecting from a non Unix machine to a remote Unix machine often the remote machine has to be told of the terminal type of the window used on the local machine What this exactly means is unimportant the important point is that without doing this the command vi used to edit files will not work correctly on the remote machine Most often the local machine runs a terminal type called vt100 To do this after logging in on the remote machine one needs to type the following in the window connected to the remote machine TERM vt100 export TERM The first line assigns the value vt100 to the shell variable TERM and the second line makes the value of this variable to the subshells of the main shell the command interpreter i e the program that makes the computer react to what you are typing on the command line after the prompt for another use of the command export see p 97 Connecting with non Unix mach
75. Unix operating systems include FreeBSD OpenBSD and NetBSD These are descendants of BSD Berkeley Software Distribution Unix developed at the University of California Berkeley in the early 1980s The Web site of FreeBSD is http www freebsd org Open Source Software Linux is a salient example of Open Source Software In Open Source Software the source code that is the code describing how the software was originally created is available to anyone for inspection In commercial software 1 INTRODUCTION TO USING UNIX 7 the source code is usually a tightly protected trade secret in order to prevent others from creating unlicensed products using the software The year 1998 was a turning point in the the history of Open Source Software this year many major corporations including Intel Sun Microsystems Oracle the second largest software company in the world and IBM announced their support for Linux The modern Open Source Movement has a long history it goes back to the establishment of the Free Software Foundation in the late 1970s see p 38 You can read about Open Source Software at http www opensource org Unix versus NT The most frequently used operating systems for personal computers are variants of the Windows operating system by Microsoft Corporation such as Windows 95 its successor Windows 98 and the more powerful Windows NT currently Windows NT 4 0 The next version of Windows 98 and that of Windows NT 4 0
76. Web For example if you are interested in information about a Unix like operating system called Linux on your personal computer you may visit the sites http www 1linuxHQ com and http www linuxworld com A wide range of computer documents about operating systems and program packages and computer use in general can be found at http riceinfo rice edu Computer Documents HDR19 A recent book about the World Wide Web written by its inventor is Tim Berners Lee with Mark Fischetti Weaving the Web HarperSanFrancisco 1999 One can leave Netscape by first clicking with the left mouse button on the word File at the top of the Netscape window and then clicking with the left mouse button on the word Erit among the choices displayed As seen from the above description the most frequently used mouse button is at least initially the left mouse button Bookmarks You can use the bookmarks feature of Netscape to save your fre quently visited Web sites By pressing the bookmarks button in the Netscape win dow you will quickly learn how to use this feature Unfortunately however you 4 X WINDOWS AND NETSCAPE 21 cannot conveniently store more than 30 or 40 bookmarks in this way since the window showing the bookmarks will become unwieldy if you try to save more book marks You might then be tempted to thin out your bookmarks and save only the most important ones but there is a better way The bookmarks are usually stored in the file bookmar
77. ad dresses do not contain commas so in most cases lines 41 45 do not do anything This is somewhat of a problem since a substitute command as in line 42 in ed that does not do anything fails to find the pattern to be substituted will cause 24 MORE SHELL SCRIPTS 117 the editor ed when called in a here document to quit For this reason if only one editing task can be entrusted to an ed here document if that task can result in failure This is why the editor ed is invoked several times in the remaining part of the script The here document in lines 46 50 deletes all spaces in line 2 of junknetscape the file containing the Web address Of course a Web address cannot contain spaces One way spaces could have intruded into line 2 of the file junknetscape was when we joined several lines in the file in line 25 or 36 since joining lines usually replaces the newline character with a space The here document in lines 50 55 joins all lines the file junknetscape currently the file contains two or three lines according as Netscape was not or was running at the time of invoking the script In line 56 the script junknetscape is invoked in the background and in line 58 the file junknetscape is removed The reason for running the command in line 56 in the background is that this returns the Unix command line where the command running the whole script currently being discussed was entered sooner without running it in the backgroun
78. age and explain how to compile and run Pascal programs in Unix Loops and conditional statements and the tracing of programs are discussed 8 Introduction to Pascal The language of computers called machine language uses certain strings se quences of 0 s and 1 s This language is very cumbersome for people to work with It was known from the theoretical work of the British mathematician Alan Turing that computers are in a sense universal machines any systematic calculation that can be done at all can in principle be done on a computer subject to space and time limitations This gradually led to the realization that instructions for a computer can be written in a way that are easier for people to comprehend than strings of 0 s and 1 s and the computer itself can be used to translate these instructions into its own machine language One can envisage a sufficiently smart computer that can take instructions in English and translate the instructions into its own machine language However there are several difficulties with using English First of all the rules of English are too complicated secondly the meaning of English is often ambiguous A compromise needs to be made the language needs to be reasonably easy for people to use it needs to be reasonable simple for the computer and it certainly needs to be unambiguous Among the first such high level languages was FORTRAN Formula Translator proposed in the early 1950 s by
79. age by typing lpr h first ps After printing the files first dvi and first ps may and perhaps should be removed by typing rm first dvi first ps in order to save disk space these files can be easily be re made if the file first tex is kept Often there are mistakes in the tex file and T X waits giving the user a chance to correct the mistake this was especially important when computers were much slower than nowadays With faster computers it is usually simpler to stop T X correct the mistake and then run TREX again One can stop TEX by holding down the control key and pressing the key c briefly this action is described as typing Control c or Ctl c often one says Ct1 C but it is important to keep in mind that lower case c is typed i e the shift key is not held down Typing Ctl c will halt or more precisely kill or terminate most programs a halted or stopped program may be resumed or continued a killed or terminated program cannot be resumed or resurrected If this does not work then some other action needs to be taken we will give some details In the file This is Tex bye there is a mistake the control sequence TeX is misspelled as Tex which is enough to seriously upset tex If the name of the above file is first1 tex then typing tex firstl will produce the message This is TeX Version 3 1415 C version 6 1 firsti tex Undefined control sequence 1 1 This is Tex
80. age would only serve to confuse the user it is best to suppress it as we did it in line 4 of the script As before line 5 clears Netscape s cache and line 6 removes its lock file 24 MORE SHELL SCRIPTS 111 Using Netscape to view HTML files revisited At the beginning of this section we presented a shell script called viewhtm1 that can be used to view HTML files via Netscape but the script worked only if Netscape was already running Here we present a script that performs the same function even if Netscape is not running 1 bin sh 2 NN file HOME htm1l_files 1 3 if test z 4 ps x grep netscape grep v grep awk print 1 P 5 then 6 rm rf HOME netscape cache 2 gt dev null 7 rm rf HOME netscape lock 2 gt dev null 8 netscape NN amp 9 else 10 rm f HOME tmp junknetscape 2 gt dev null 11 touch HOME tmp junknetscape 12 ed HOME tmp junknetscape lt lt heremark 2 gt dev null 13 Oa 14 netscape remote openURL NN new window 15 16 w 17 q 18 heremark 19 HOME tmp junknetscape 20 rm f HOME tmp junknetscape 21 fi If we call this script viewhtm11 then the command viewhtml1 special_files example html will use Netscape to display the file html_files special_files example html in your home directory If you use this command the shell variable NN in line 2 of the script evaluates to file HOME html_files special_files example html In lines 3 21 we have
81. al directory in line 10 we used 2 gt to redirect the standard error output instead of gt amp used in line 3 of the earlier script the two have the same meaning in line 12 we suppressed the standard error output of the ed command while in the earlier script we did not do so in line 5 Finally many os lines 10 20 are indented to indicate to the reader the computer does not care that these lines are part of the conditional command in lines 3 21 However lines 13 18 of the here document starting on line 12 cannot be indented In fact line 18 cannot be indented since the mark signifying the end of the here document must start at the beginning of the line lines 13 17 must not be indented since in the commands given to the editor ed every character in a line is meaningful For example for the ed command in line 15 to work there must be only a single period in the line so as to put the editor into command mode from insert mode indenting line 15 would disable the script Indenting lines 13 14 16 and 17 would not disable the script adding two spaces at the beginning of line 14 would add these two spaces at the beginning of the single line of the file junknetscape being edited but these spaces would cause no harm for the command in line 19 As we mentioned above some of the above scripts may fail when invoked from a directory where the user has no read write or execute permission For example the script viewhtml10 on p 103 may fail
82. ame way as the corresponding lines did in the original program performing the Euclidean algorithm presented on p 55 In line 14 the statement rewrite outfile open the file called outfile for writing as the first step if this file already exists its contents will be erased and if it does not exist it will be created In lines 15 17 the write and writeln statements work as usual except that the first argument outfile of these statements indicate that the writing should be done into the file called outfile rather than to the standard output i e the terminal display screen 16 Representing the Greatest Common Divisor as a Linear Combination The greatest common divisor of any two integers can be written as a sum of mul tiples of these integers Instead of sum of multiples we will say linear combination since this perhaps more intimidating term is the one commonly accepted in the mathematical literature For example the greatest common divisor of 422 and 546 is 2 and we have 2 422 22 546 17 This is such an important observation that we will formulate it as a theorem THEOREM For any two integers a and b at least one of which is assumed to be different from 0 there are integers x and y such that a b ax by It is important to assume that not both of the numbers a and b are zero since as we mentioned above the greatest common divisor 0 0 is meaningless 60 IV APPLICATIONS OF PASCAL The reason this i
83. and texview first amp You can find out what aliases are in effect during your session by typing alias The reply you receive may be something like this alias cp cp i alias mv mv i alias rm rm i alias cdtexbase cd usr lib texmf texmf tex amstex base alias texview xdvi s 4 thorough The first three among these are there for your protection They specify the interactive option for the commands cp mv rm since each of these may destroy files by copying or moving something else over them or by removing them so before a file is lost you are queried asked by the computer if you really want to lose the file If you do not want to be protected this way you might delete these aliases or better yet comment them out by placing the pound sign at the beginning of the line recall that is the shell comment character Source scripts As an alternative to aliases you can write a command into a file and source the comment That is if you have a file called cdbase with the content cd usr lib texmf texmf tex amstex base then typing cdbase will get you to the directory in question In fact on typing the last line the computer takes the commands from the file cdbase and executes them in order as if these commands were written on the command line that is changes of directory or shell variables will take effect On some systems the command cdbase also works cf 38 but it may or m
84. and these three spaces and the two characters in the number 15 make up the width of 5 Note the role of the space before the quotation mark in line 5 this space ensures that the word is and the number 15 is separated by a space that is the space is printed as part of the quoted text If one omits this space i e if one replaces line 5 with the following writeln The number is num 1 then the printout will look like The number is15 If one wants a period at the end of the line printed out i e if one wants the printout The number is 15 then a third item needs to be added in the writeln statement that is line 5 needs to be modified to read writeln The number is num 1 Every statement must be followed by a semicolon except the statement directly preceding the key word end hence there is a semicolon at the end of line 4 but there is no semicolon at the end of line 5 In fact putting a semicolon at the end of line 5 would cause no harm Placing a semicolon at the end of line 5 will add an empty statement after the semicolon and before the separator preceding the key word end To write the empty statement one uses no characters that is the empty statement is really nothing when written down and it has no effect its presence is indicated only by the presence of semicolon This remark does not imply that one can add semicolons at any place at will a lot of trouble is caused by misplaced or missing semicolons in Pa
85. ape bookmarks html However this action is not taken immediately First Netscape just remembers the item so you can use the added bookmark immediately and it adds it to the above file with some delay amounting to perhaps 30 seconds or even some minutes If you kill Netscape in the meanwhile the bookmarks htm1 file does not get updated while if you leave Netscape the regular way the file does get updated A more concise script to kill Netscape Unix is known for its terseness In line with this reputation the above shell script killns can be rewritten in a much more concise way 1 bin sh 2 kill s 9 3 ps x grep netscape awk print 1 cat 4 2 gt dev null 5 rm rf HOME netscape cache 6 rm f HOME netscape lock To avoid any confusion with the earlier script call this new script killns0 First notice that this shell script contains a single command since the first two end of line characters of this three line command are quoted This command has the following syntax commandi command2 to indicate that we are discussing a command typed on the command line we added the prompt on the left Here command1 stands for kill s 9 which is a sure kill and command stands for ps x grep netscape awk print 1 cat This command uses a repeated pipe and writes to the standard output the same information as lines 2 4 of the script killns above writes to the file junkki
86. ariable yearcount calculated in line 60 counts the number of days with multiples of 7 neglected from January 1 1 A D to the year in question for this one simply has to add the number of leap years to the number of the year in questions so that leap years are counted twice while regular years are counted only once this is because 365 gives a remainder of 1 when divided by 7 while 366 gives a remainder of 2 In line 63 the number of days elapsed in the year in question is added and the remainder when dividing by 7 is taken This remainder corresponds to the day of the week to figure out which remainder corresponds to which day one needs to run the incomplete version of the program with a recent date where the date of the week is known Having done this one can make the correspondence between the value of the remainder and the days of the week this is done in lines 68 76 On line 77 the day of the week in question is printed out 78 V MISCELLANEA CHAPTER V MISCELLANEA A short glimpse of the mathematical typesetting language TFX is given in order to write about mathematics today the tool of choice is T X rather than any of the standard word processors A basic introduction to using plain vanilla Unix elec tronic mail is given then some shell scripts are discussed that facilitate the writing and sending of electronic mail Next source scripts are discussed for changing the Unix environment e g changing directories
87. ark that is not visible in the Web page Comments are useful for the persons designing and maintaining modifying updating the Web page The form of a comment is lt teaxt gt The pair of tags lt ADDRESS gt in line 20 and lt ADDRESS gt in line 33 enclose the address of the author of the Web page they make the information placed between them appear in italics This tag is used more for documentation than for formatting the page In lines 24 and 25 the pair of tags lt A gt lt A gt enclose what is called an anchor part of the text on which you can click with the left mouse button to produce some action such as moving to another Web page The tag lt A gt requires at least one option that is this tag never occurs by itself it is followed by further information between the symbols lt and gt The most important 6 HYPERTEXT MARKUP LANGUAGE 27 Attila Mat s Home Page Attila M t Department of Mathematics Brooklyn College 2900 Bedford Avenue Brooklyn NY 11210 2889 USA e mail mate sci brooklyn cuny edu office phone 718 951 5246 Photograph by C J Mozzochi To see my letter sent to the London Sunday Times in response to a negative article about Linux click here To my knowledge the let ter has not been published in the London Times You may prefer to read a discussion of the London Sunday Times article first To do this click here This discussion has links both to the ori
88. ave used the percent sign here but we wanted to show that there are other possibilities That is lines 6 10 work as if commands issued to the editor ed after typing the command ed junknetscape The ed command 0a in line 6 indicates that the next line is to be added after line 0 of the file being edited namely of the file junknetscape In this line the shell variable NN is evaluated to its value assigned on line 2 i e to the whole line will become netscape remote openURL file home jsmith html_files examp le html new window Note that this is a single line of the file but since it is too long to display it in a single line the end of the line is scrolled into the next one but there is no end of line character in this text except at the very end The lone period in line 8 indicates the end of things to be added w in line 9 instructs the editor ed to write the result of the editing to the file being edited junknetscape in the present case q in line 10 makes ed quit and the percent sign in line 11 signifies the end of the here document The meaning of the first period in line 12 is that the commands contained in the file mentioned next in the line are to be executed as if they were written out explicitly The file junknetscape is referred to as junknetscape here the period refers to the present working directory so the two ways indicated describe the same file but in some situations using the latter way has certain
89. ay not take the file cdbase from the present working directory it may instead take it from the first directory it finds among those listed in the PATH shell variable and the latter command may not work at all if the present working directory is not included in the PATH variable cf 98 Hence the first version is definitely preferable The above command works in the Korn shell in the Bourne shell and in the Bourne again shell bash in C shell to accomplish the same thing one should type source cdbase Hence the expression sourcing a file The problem with the command cdbase is that it works only in the directory the file cdbase is located This is clearly not practical since you may want to change to the above directory with the long name 25 SOURCE SCRIPTS 123 from wherever you are To do this you can put the following aliases into the kshrc file in Korn shell in bash you put it in the file bashrc alias sc pwd gt HOME 1lib sources sc junk cd HOME 1lib s ources Note that this is a single line that wraps over into the next line and not two lines In fact for this line to work it must not be broken up The meanings of the commands in this alias are fairly straightforward their intention is not so We will explain how this works later here we only mention that the semicolon is used to separate two commands in fact even on the command line you can write several commands separated by semicolons The f
90. be achieved by repeated com pression In any case Netscape cannot handle images compressed by gzip that are linked to automatically load into a Web page even if you set up Netscape to handle compression On the other hand if you enabled Netscape to handle both PostScript files and compressed files it will also be able to handle compressed PostScript files as one would expect This is very useful since PostScript files are not compressed and a significant reduction in their size can be achieved through compressing them by gzip Enabling Netscape to handle compressed files has a side effect similar to the one we mentioned above in connection with PostScript When clicking on a link to a file with a name ending in gz Netscape tries to view it rather than download it This may be a problem since many such files are not viewable at all To handle this problem it is always safe to shift click on such a link rather than click on it If you accidentally clicked on such a link to a file called say ftp acc5 its brooklyn cuny edu pub mate somefile tar gz stand by you do not need to stop Netscape Netscape will download the file somefile tar gz into it chache see p 21 and when the download finishes which may take some time if the file is large netscape will display an error window saying something like unknown suffix this refers to the suffix tar in the file name If That is it cannot handle a file called picture jpg gz obtained
91. can easily be convinced that of the numbers x and y in the equation ao bo aox boy one is positive and the other is negative In the final version of the program we check which of them in negative and then put that number in parentheses so as to obtain the nicer printout 2 422 22 546 17 Here is the program 1 program euclid input output 2 The greatest common divisor d of two positive 3 integers a and b entered at the keyboard is 4 calculated and is represented in the form d ax tby 5 where x and y are integers 6 vara b a0 bO q x y x1 y1 temp 7 tempx tempy integer 8 begin 9 write Type a a must be a positive integer 10 readln a 11 write Type b b must be a positive integer 12 readln b 13 a0 a bO b 14 X aS 0 y t 13 15 1 pecs yd pS 03 16 while a lt gt 0 do 17 begin 18 temp a 19 q b div a 20 a b mod a 21 b temp 22 tempx x1 tempy y1 23 xl x q x1 yl y q y1 24 x tempx y tempy 25 end 66 IV APPLICATIONS OF PASCAL 26 Error check commented out in the final version 27 if b a0 x bO y then 28 writeln The result is correct 29 else 30 writeln The result is not correct 31 if x lt 0 then 32 writeln b 1 a0 1 x 1 33 b0 1 y 1 34 else 35 writeln b 1 a0 1 x 1 36 BOs Cyr 79 37 end
92. can type sc return This will cause the command in this file i e the command 25 This is not quite true in Korn shell it can be broken up as alias sc pwd gt HOME 1lib sources sc junk cd HOME 1ib sources while in bash it can be broken up as alias sc pwd gt HOME 1lib sources sc junk cd HOME 1ib sources The Korn shell line break will not work in bash and the bash line break will not work in the Korn shell The C shell version is completely different alias sc pwd gt HOME 1lib sources sc junk cd HOME 1ib sources source I have not experimented with how to break this up 26Depending whether or not is included in the PATH variable and on other factors such as the shell used etc the command sc cdbase might also work but the command given in the main text is preferable 124 V MISCELLANEA cd cat sci junk to be executed the result of the command between the left quotes is the content of the file sc1 junk in the directory HOME 1ib sources which is the directory where we started out this was assumed to be usr lib X11 so the command cd changes back to this directory Note the reason for the line mv sc junk scl junk in the file cdbase When we type sc return the first command in the sc alias would have overwritten the file sc junk and its content would have been lost had this file not been moved to scl junk Observe that in Korn shell and in bash you can change back to the p
93. cated by s1 and bold face thick letters by bf In line 29 the control sequence par indicates the beginning of a new paragraph Again the line break has no effect and a new paragraph would be started even if lines 29 30 were replaced with 3 2 4 2 5 2 par It is generally assumed that Fermat As mentioned above new paragraphs can also be indicated by blank lines in fact using a blank lines instead of the control sequence par would have been better because that would give a better appearance to the tex file it would be easier to ascertain where the paragraphs are We used this control sequence here only as an illustration of a different way of accomplishing the same thing Writing par par and even adding blank lines has no new effect the result will be the same as if par had been written only once 21 MATHEMATICAL TYPESETTING 85 Lines 44 47 begin with the percent sign the percent sign introduces a comment and everything in the line following a percent sign will be ignored by the tex program i e it will not appear in the printout Here the comments in lines 44 47 were written by to author to indicate how the text may need to be revised If you really want a percent sign in the text you can type this percent will be typeset as and will not be interpreted as a symbol introducing a comment similarly to get a dollar sign you need to type this will be typeset as and will not be interpreted as a dollar sign used
94. characters such as e g etc You log in to the computer by typing your login name and when the computer asks you to do so your password When you type your password it will not appear on the screen this is a security measure in case someone is looking over your shoulder After you have successfully logged in the computer displays a short message about itself and afterwards it displays a few symbols at the beginning of the line this is called the prompt meaning that the computer prompts or invites you to type something or more precisely the shell prompt The prompt may be something as simple as the single character or or a short message including the name of 1The computer understands the commands that you type through a layer called shell that translates your commands into the computer s own language 8 I UNIX the machine the directory location see below or a line number In our examples below we will use for the prompt Changing your password If you do not like your password this is the time to change it to something you can easily remember but it follows certain rules about containing upper and lower case characters numbers etc Be prepared that changing your password can be somewhat disruptive For ex ample the Sun Workstations at the Atrium are programmed to log you out and prevent you from logging in for about half an hour after changing your password Further these computers are also p
95. chosen by the user at will with the following content This is TeX bye The character called backslash plays a special role in TeX it introduces what are called control sequences In the above file there are two control sequences TeX which produces the tex logo TX the other one is bye indicating the end of the tex file To typeset this file type tex first 21 MATHEMATICAL TYPESETTING 79 assuming that the name of the above file was first tex as usual the sign at the beginning of the line stands for the prompt If everything goes well and often it will not as we will discuss soon after the tex program finishes two files will be produced first dvi and first log Not surprisingly the first file is usually called dvi file pronounced D V I and the second one log file the file first tex is usually called tex file tex is pronounced tek Here DVI stands for device independent which refers to the fact that it contains information that any kind of printing device supplied with appropriate computer software should be able to use the dvi file to print the document The log file contains a log i e list of actions taken by the TEX program this is usually an extended version of what it writes on the screen If you become familiar with TeX you will find the information in the log file very useful at this point it may be somewhat confusing The next step is to preview the printout on the screen Assuming that you ar
96. control of in Unix 34 empowering 29 35 link 20 lock file of 21 108 quitting 20 shift click in 31 Neumann John von see von Neumann John New York Public Library remotely connecting to computers from 129 not in Pascal see Pascal key word not number binary 18 octal 18 object program 39 91 Open Source Software 6 OpenBSD 6 OpenWindows 19 option in Unix commands 11 or inclusive 68 or in Pascal see Pascal key word or ordinal type in Pascal see Pascal ordinal type in output standard 57 output in Pascal see Pascal output in output stream 107 packed character in Pascal see Pascal packed character in par see TeX par paragraph in T X new see T X paragraph in new Pascal 5 36 51 arithmetic expression in 42 priority rules for 42 assignment in 40 42 body of program 38 boolean type in 69 case statement selector in 74 case statement in 74 char type in 73 character in see Pascal char type in comment in 51 compiling programs 37 constant in 51 declaration in 40 empty statement in 41 file handling in 57 59 for statement control variable in 73 for statement in 73 identifier 38 input in 43 integer overflow in 48 integer type in 40 key word see Pascal word symbol key word and 71 key word array 73 key word begin 38 44 key word const 51 key word div 42 63 key word end 38 44 key word mod 42 54 key word not 70 key word or 71 ke
97. ctory texinputs of the parent directory of the current directory The operating system DOS would apparently have some difficulty with using such references to locations in the directory tree since DOS uses backslash instead of slash in describing the directory tree The line input texinputs mytex would not work in TX since backslash is a special character in T X Setting up your own texinputs directory The input control sequence in addition to recognize the Unix directory tree as discussed just before can also take files certain special directories without having to state the directory tree For example when you type input amstex cf p 81 in Red Hat Linux 6 0 the file usr share texmf tex amstex base amstex tex is used That is when you type 86 V MISCELLANEA input somefile the file somefile tex is taken from your working directory or if there is no file by that name then it is taken by certain directories specified by the by the T X program You can add to the directories searched by the T X program to find this file In order to do this you may add the lines TEXINPUTS HOME texinputs export TEXINPUTS in your profile or kshrc file in Korn shell ksh or in your bash_profile or bashrc file in the Bourne again shell bash The first line assigns a value to the shell variable TEXINPUTS and the second line makes this value available to various programs cf the footnote on p 98 With this c
98. d The option i stands for interactive That is for each file encountered that you get a question whether you want it removed If the file is called say whatsit you get the question rm remove whatsit and you have to answer this question with y or n for yes or no If there are too many files to be removed this may get to be too cumbersome the option f is used to override the option i If you are in the directory netscape cache you can type rm rf instead of the command given above This command is however very dangerous since it removes everything in the directory that you happen to be in if you type this line mistakenly believing that you are in the netscape cache directory the result can be disastrous In fact the first version of this command given above is also somewhat dangerous and it may be altogether safer to use a shell script to clear Netscape s cache see p 99 in Section 23 5 Starting to Build Your Own Web Page If you have an account on the Unix network at the Atrium you can build your own Web page To do this as the first step you need to make your home directory accessible to the Web server by changing its permission code to 711 You can do this by typing cd chmod 711 Here the first line puts you into your home directory if you already there it is unnecessary but you can still type it since then it will do nothing The second line changes the permission code of your home directory Th
99. d one might have to wait a few seconds before one can enter the next command However running the command in the background occasionally introduces some timing problems the file junknetscape is removed by the command on line 58 before the command on line 56 is able to make use of this file To prevent this the command on line 57 was added this command has no other effect it updates the time of last change of the file junknetscape but this has no importance since the file is going to be removed anyway Going to a Web site given in a file a variant A variant let us call it netfreadO or the above shell script is as follows bin sh if test s 1 then echo go to URL given in file listed as argument exit 0 fi if test f 1 then echo file 1 does not exist exit 0 oono RAUN e 11 fi 12 if test z 13 ps x grep netscape grep v grep 14 awk print 1 cat 2 gt dev null 15 then 16 rm rf HOME netscape cache 17 rm rf HOME netscape lock 18 rm f HOME tmp junknetscape 2 gt dev null 19 touch HOME tmp junknetscape 20 ed HOME tmp junknetscape lt lt heremark 2 gt dev null 21 Oa 22 netscape 23 24 1r 1 118 V MISCELLANEA 25 2 j 26 2s 27 2s 2C g 28 2s 2C 29 28 30 2s g 31 1 23 32 w 33 q 34 heremark 35 else 36 rm f HOME tmp junknetscape 2 gt dev null 37 touch HOME tmp junknetscape 38 ed HOME
100. d by the user and not printed by the computer If the program is run with n 99000 then the condition in line 6 is satisfied and so the statement in line 7 is executed The printout will be as follows Type n n must be a positive integer 99000 n is too large Maintenance and portability issues Since writing computer programs is very time consuming it is desirable to make programs easily portable i e trans ferable from one computer to another Even when you do not intend to port your program to a different computer you may still want to maintain it That is the environment on the computer you are using may change A newer version of the operating system or an improved version of the Pascal compiler may be installed sometime a newer version thought to be an improvement turns out to be worse than the older version In any case a program that ran perfectly in the old environ ment may have to be changed that is maintained to suit the new environment Here is a version of the above program that takes these considerations into account e program example5 input output This program calculates the sum of integers between 1 and n n is entered at the keyboard and it must be positive If n is larger than the constant largestn the program notifies the user that the calculation cannot be done by the program The value of this constant is implementation dependent and it may have to be changed when porting the program
101. d directory All your subsequent Pascal programs should be put in this directory when you have too many Pascal programs you may create a number of different directories to organize them As the second step this program must be compiled that is translated into the computer s own machine language This is done by invoking the Pascal compiler usually called pc pc s first_program p o first_program comp That is the Pascal compiler pc is invoked with the s standard option to compile the program called first_program p and to produce a compiled program i e executable machine language program called first_program comp you may chose a different name if you are not a good typist you may want to choose a simple short name such as say ex1 for the compiled program The option o in the above line stands for object file and indicates that the object file produced by the compiler i e the executable program should be given the name following this option The command can also be typed without the o option pc s first_program p In this case the computer chooses the default filename a out as the name of the compiled program Your computer may not have a Pascal compiler installed or 38 HI PASCAL else it may have have several Pascal compilers having different names a well known one is gpc which stands for GNU Pascal Compiler written by the Free Software Foundation You may read about the Free Software Foundation at http www
102. de Web see below The text begins on line 1 with the tag lt HTML gt which indicates that the following text is an HTML document this tag comes with a pair lt HTML gt on line 67 indicating the end of the HTML document Some tags come singly others come in pairs in the latter case the second member of the tag is preceded by aslash Also note that the tags are enclosed between the symbols lt less than and gt greater than Header information is placed between the par of tags lt HEAD gt and lt HEAD gt see lines 2 and 4 and as part of the header information the title of the Web page is placed between the pair of tags lt TITLE gt and lt TITLE gt The title of the Web page is not part of the information displayed on the Web page itself it is displayed in the title bar at the top Note that we used capital letters in tags so that they can be easily identified however tags are not case sensitive i e they can just as well be written lower case The tags lt title gt and lt TITLE gt mean the same thing The main part of the Web page is placed between the tags lt BODY gt on line 6 and lt BODY gt on line 66 Note that leaving blank lines such as lines 5 and 7 has no effect The new line character and the space character in the file are treated the same way and if they occur in the text several space and new line characters have 26 Il THE WEB the same effect as a single space character a space between wor
103. determined by the shell variable PATH in Korn shell Bourne shell or Bourne again shell in C shell the variable may be called path the machines at the Atrium run Korn shell as its default shell so most of our comments will apply to the Korn shell You can find out its value by typing echo PATH The first dollar sign in this line is the shell prompt the second one is used to get the value of the shell variable The response you get may be something like bin sbin usr bin usr sbin usr local bin usr local sbi n usr bin X11 usr X11R6 bin root bin usr local sbin The directory name bin is short for binary and it is customary to store executable files in a directory called bin even though many of these files are not binary files they may be text files such as shell scripts Note that the above display is a single line but it wraps around two lines because it is too long that is there are no end of line characters in this display The colons are used to separate locations When you type the name of an executable file the system will search in turn the directories bin usr bin usr sbin in this order until it finds the name you typed The value of the PATH variable is called the search path or execution search path since it contains a list where executable programs are searched If the command you typed is something that is not found there will be a message telling you this for example if you want to list the file
104. ds Line breaks in the displayed text can be forced by the tag lt BR gt this tag has no pair it is a solitary tag The three tags occurring on line 8 are lt BR gt lt HR gt lt BR gt The first and third of these forces line breaks resulting in vertical spaces left that correspond to the space taken up by a line The middle tag lt HR gt is a horizontal rule horizontal line this tag also a solitary tag The pair of tags lt CENTER gt on line 9 and lt CENTER gt on line 12 indicates that the text between them should be centered and the pair of tags lt H1 gt on line 10 and lt H1 gt on line 11 indicates that the text in between is a heading set in large type there are six different levels of headings lt H1 gt lt H1 gt being the largest and lt H6 gt lt H6 gt being the smallest The letter with the acute accent is produced by the string amp aacute including the semicolon in line 10 while the letter in the same line is produced by the string amp eacute including the semicolon The line break at the end of line 10 and the several space characters at the beginning of line 11 appear as a single space in the displayed text The tag lt IMG gt in line 15 is used to include an image picture in the Web page The expression ALIGN LEFT involving the attribute ALIGN and its value LEFT indi cates that the image should be on the left of the page Tags in HTML describe elements that is part of the document
105. ds I have found a marvelous demonstration of this but there is not enough space on the margin to write it This statement is now called Fermat s Last Theorem Observe that for n 2 the above equation has many solutions the simplest one is 3 4 5 It is generally assumed that Fermat did not have a proof of his Last Theorem In the first place he never announced the general statement publicly but he repeatedly made public statements about the special cases n 3 and n 4 as late as 1659 Probably he found a mistake in his original proof and was able to prove only special cases He had no reason to retract a statement he never made in public Fermat s Last Theorem was finally established by Andrew J Wiles of Prince ton University in 1994 You can read more about its history at http www coe uncc edu cas flt html Next we explain line by line the meaning of the text in the above file In line 1 the resources of amstex also written as AMS T X are requested AMS T X is the version of TEX used by AMS the American Mathematical Society It supports the typesetting of more mathematical formulas than regular TX called Plain TX another popular package is Later Line 2 specifies that that the style file amstppt which stands for AMS Preprint Style is to be used This is a widely available style file Books or mathematical periodicals may have their own style file so that the same input file can be made to appear differ
106. duct of four or more integers We can now use the above lemma or rather its extension to a product of more than two factors to present the PROOF OF THE FUNDAMENTAL THEOREM OF ARITHMETIC Assume on the contrary that there are positive integers with two different prime factorizations Let n be the smallest such integer and let its two different prime factorizations be n p p2 Pk 192 M Note first that each of the primes p must be different from each of the primes qj Indeed if for example we had p q then the number n p P2P3 Pk Q203 q would be a number smaller than n with two different prime factorizations in con tradiction with our assumption On the other hand the equation above shows that the prime number p is a divisor of the product q q2 q So by the lemma above or rather by its extension to more than two factors at least one of the numbers q1 q2 qu say qj for a certain 19 TRUTH TABLES 69 j with 1 lt j lt l must be divisible by p As qj is a prime its only divisors are 1 and itself As p being a prime is different from 1 we must have p q This is a contradiction since as we stated above p must be different from q This contradiction shows that our initial assumption was wrong that is there are no integers with two different prime factorization The above method of proof involving the consideration of the least positive inte ger with a certai
107. dvertently made changes while using view you cannot quit the editor in a normal way To quit in command mode you need to type either 7q to force a quit without saving a changes or wq to force a quit while saving the changes see the discussion of command line mode in vi on p 15 28A book about Red Hat coauthored by Red Hat s CEO Young is Robert Young Wendy Goldman Rohm Under the Radar Coriolis 1999 29In Solaris SunOS 5 5 1 the same file is called var adm messages and is readable by every user 128 V MISCELLANEA The problem you have to deal with when using vi to find out your IP address is that the file var log messages may also contain your IP addresses from past ppp sessions and you need to look at your last local IP address given in this file Using the tail command makes this problem easy to handle This command tail writes the last few lines of the file on the screen and its f option writes keeps writing new lines as lines they are being added to end of the file So if you type the commands as superuser cd var log tail f messages just before connecting to your Internet provider your local IP address will be written on the screen by this command at the time the connection is established Thus in addition to finding out your IP address you can use this command to monitor whether your connection is properly established After you have seen enough you must stop the the tail command by typing Control c
108. e as mentioned above HOME refers to the user s home directory In order for this command to work the file HOME marks regards will have been created with the following content 1 2 Regards 3 4 J F Smith 5 jsmith math myschool edu 6 http www math myschool edu jsmith The name of this file regards refers to the way this letter is signed Other signature files called best sincerely truly etc can also be created Lines 3 18 contains what is called a here document The commands in these lines are not commands to the shell they are commands to a text editor called ed ed is a basic line editor in Unix its commands are somewhat similar to some of the vi commands in command and command line mode in fact vi is based on the line editor ex which is a successor of ed The above shell script could have also been written by using ex instead of ed but ed appears to be more widely available than ex Line 3 specifies that the subject of this here document is the program program ed with the argument 1 this latter refers to the first argument on the command line running the script letter i e 1 refers to the file cmuser5 That is lines 4 17 work as if they were issued on the command line after having typed ed cmuser5 on the command line with important qualifications concerning lines 5 and 9 to be mentioned below The marks in lines 3 and 18 indicate the beginning and the end of the here document Other marks consi
109. e a user on her machine or she lets you know her login name and her password you cannot log in and IP_address is the IP address of her machine If your Internet connection ties up your only phone line you can still communicate in writing with your friend by using Unix s talk command You can do this by typing talk 1 yourfriends_login_name IP_address where yourfriends_login_name is the login name of your friend on her machine and IP_address is the same IP address that you used to log into her machine You would normally type this command in a window representing your own machine and not in the window you used to log into her machine though the command should also work in the latter window 130 SOLUTIONS 28 Solution to Problem 1 in Section 16 a 25 14 14 14 11 14 3 14 2 14 1 14 c 645 242 242 242 161 242 81 242 80 242 1 242 e 735 141 141 141 30 141 21 141 9 141 3 141 0 1 2 3 5 8 645 645 0 645 645 1 645 2 645 3 735 735 0 735 735 4 735 5 735 14 b 488 384 0 4 384 384 1 4 104 384 1 72 384 4 4 32 384 5 8 384 14 d 122 48 0 4 48 48 1 4 26 48 2 22 48 3 4 4 48 5 4 2 48 28 f 984 452 0 4 452 452 1 4 80 452 2 4 52 452 11 4 28 452 13 24 452 24 4 452 37
110. e considered as a single compound statement Normally a compound statement is made up from more than one statements However in our first pro gram the one printing Hello world the body of the program was a compound statement made up of a single statement The key new feature of this program is however the while do statement in line 8 in fact as we will see in a moment this statement occupies lines 8 12 The syntax i e the form of the while do statement is as follows while condition do statement In the present case the condition is i lt n and the statement is the compound statement in lines 9 11 here the meaning of lt is lt that is less than or equal to the keyboard does not allow one to write lt Its semantics i e its meaning can be explained as follows When the execution of the program arrives at the key word while the condition is checked If the condition is satisfied the statement is executed and the sequence of the execution of the program continues at the key word while If the condition is not satisfied then the statement is not executed and the execution program continues with the next statement in the sequence in the present case this is the statement in line 13 11 LOOPS 45 As we will see under normal conditions the while statement in lines 8 12 is ex ecuted repeatedly a number of times statements that are supposed to be executed repeatedly a number of times under normal conditions
111. e dot in this line refers to the directory you are currently in the present working directory which will be your home directory since you just changed to it in the preceding line Permission codes and the command chmod were described above The permission codes assigned 6 HYPERTEXT MARKUP LANGUAGE 23 by this will allow anyone in the world to enter your home directory without being able to make any changes in it and without being able to read its content that is someone entering your home directory and then trying to list the names of the files in it by typing 1s will get a reply such as unreadable or something similar As the next step you need to make a directory called public_html in your your home directory by typing mkdir public_html Here html abbreviates Hypertext Markup Language what this is will be explained later Next the correct permission codes must be assigned to this directory this can be done by typing chmod 711 public_html As we mentioned above permission codes assigned by this will allow anyone in the world to enter this directory without being able to make any changes in it and without being able to read its content At this point you should enter this directory by typing cd public_html In this directory a file called index html with permission code 644 must be created this can be done by the following commands touch index html chmod 644 index html Here the command touch create
112. e in an X Windows environment such as OpenWindows this can be done by using the program zdvi this allows you to view the result produced by the dvi file Type xdvi s 4 thorough first amp Here the option s introduces the shrink factor 4 a larger number will produce a smaller display and the option thorough influences the behavior of the xdvi program on color displays if you are really interested in the details you can read the on line manual pages of sdvi The value 4 may be replaced by something else depending on the set up and on the size of the display window required Finally the symbol amp at the end of the line ensures that xdvi will run in the background The effect of this that you will receive a prompt in the window in which you typed the above line and so you can continue to use this window even while xdvi is running i e while its display window is open Typing the above line will result in the opening of a display window One can close this window by typing q in it i e typing q while the mouse pointer is in this window If the document extends to several pages one can go to the next page by typing n or f for forward in the display window typing 3n or 3f will go three pages forward Typing 4b or 4p will be back four pages p for previous while n and p will go back one page Typing 7g will take you to p 7 while typing g alone will display the last page The display at present will be a single line T
113. e in two kinds Syntax errors these are errors in the form of the program i e errors in following the grammar of the language in which case usually the computer will not be able to understand what is intended by the program and semantic error or logic errors there are errors in the meaning of the program i e the computer is not is able to understand the action described in the program but the action described is not what is intended The compiler usually finds and lists the syntax errors though the error messages given by the compiler are often hard to understand Logic errors are hard to find they can often be found only after extensive testing and subtle logic errors are often found only after long use of the program if at all Since a program cannot even be compiled if it has syntax errors the first task is to correct the syntax errors and only then is it possible to deal with logic errors A good way of correcting syntax errors is to work with two windows one for com pilation another for editing the source program this is the file first_program p in the example above that is the program as written the compiled program first_program comp in the above example is called the object program In the first window the program is compiled repeatedly in the second window some cor rections suggested by the compiler error messages should be made When doing this the file containing the program should be open
114. e of the machine you want to be connected to this is usually all lower case letters and you must have found out the name of a machine by having typed hostname while connected to the machine on an earlier occasion The login name in the above command can be omitted i e one can type rsh machinename its brooklyn cuny edu instead Here rsh stands for remote shell If both the remote and the local machine run Unix you can even display X windows graphics created by the remote machine on your local machine To do this you need to type xhost machinename its brooklyn cuny edu before logging in or in a separate local window For this you must have opened X windows on the local machine If you are permanently connected to the Internet and have your own host name the name of your machine by which it is known on the Internet and domain name the name such as its brooklyn cuny edu by which your machine or your local network is found on the internet then after logging in you can type DISPLAY hostname domainname 0 0 export DISPLAY where of course hostname and domainname need to be replaced by the actual host name and domainname When you are connected to the Internet from your home it is more likely that you do not have your own host name and domain name In this case after logging in on the remote machine you need to type DISPLAY local_IP_address 0 0 export DISPLAY where local_IP_address is the IP address Internet Pr
115. ean variable leapyear will be true if the given year is a leap year this will be important in calculating the number of days to the date in question in the given year In lines 14 18 a message is written to prompt the user to enter the date in line 19 the date entered is read The readin statement in this line will assign the first number entered to the variable month the second one to the variable day and the third one to the variable year In lines 21 22 it is decided if the year in question called current year in the comments is a leap year If it is the boolean variable is assigned the value true otherwise it is assigned the value false In lines 28 39 the length of each month is entered while multiples of 7 are neglected that is for example 2 is entered for September in line 36 since September has 30 days and the remainder of 30 divided by 7 is 2 The length of February is considered to be 28 days the case of leap years will be taken into account later in line 43 In lines 48 50 the number of days in the year in question is calculated and this value is assigned to the variable daystocurrent see the discussion of the for statement above As we mentioned several times before 20 DAY OF THE WEEK 77 multiples of 7 are neglected here In lines 57 59 the number of leap years from the year 1 B C is calculated this calculation uses the fictitious assumption that the Gregorian calendar has been used since that date The v
116. ear will be used to store the day month and year in the date about which the day of the week is to be established This date will be typed at the keyboard The variable daystocurrent will be used to calculate the number of days to and including to the day in question in the given year in this calculation multiples of 7 may be neglected In line 9 in the variable leapyearcount the number of leap years are counted from the year 1 A D as if the Gregorian calendar had been in effect from that date Even though the Gregorian calendar has not been effect for that long this will not cause problems in comparing recent dates for which the Gregorian calendar is valid In the variable yearcount the number of years are counted since year 1 A D with leap years counting double the reason for this is that 365 divided by 7 gives a remainder 1 while 366 divided by 7 gives a remainder 2 In the variable daycount the number of days from January 1 of the year 1 A D are counted neglecting multiples of 7 This is done only formally since as we already mentioned the Gregorian calendar has not been effect that long for comparing days of the week for recent dates this is however of no consequence As a point of interest note that there was no year 0 A D year 1 B C was directly followed by year 1 A D since we only consider recent dates this is again of no consequence for us We already discussed the array declarations in lines 10 and 12 in line 11 the bool
117. ecause we used the f force i e do the copying even if it is destructive option of the copy command cp Second in order for this to work your Web page has to have been set up already as explained in Section 5 If the address of your Web site is say http www website someuniv edu cmuser then you can find the above file at the address http www website someuniv edu cmuser example p Note that even though the file example p is not written in HTML it can still be displayed on the Web In fact what is displayed is the file itself whereas in case of an HTML file what is displayed is what is meant to be seen and not the file itself 100 V MISCELLANEA in fact the latter contains formating commands describing what is to be seen If you want to see an HTML file itself on the Web by using Netscape you need first to press on the word View in the top row of the Netscape window with the left mouse button and then to press on phrase Page Source among the choices displayed again with the left mouse button CLI versus GUI Currently there is much debate whether computers should have Command Line Interface CLI or Graphical User Interface GUI pronounced goo ee GUI allows non dedicated users to quickly learn how to do sophisticated things on the computer CLI allows them to automate repetitive tasks by using shell scripts at least at present shell scripts do not allow you to automate sequences of mouse clicks used to work with GUI
118. ed meanings These are program begin writeln and end key word is somewhat colloquial as far as the formal description of the Pascal programming language is concerned the proper name for key words is word symbol key words are also called reserved words indicating that they they cannot be used outside their strictly defined roles The word program introduces the program heading the first line where the program is given the name hello and it is indicated by the word output that the program will write to the output file which at present is the window in which you are working The program heading must be followed by a semicolon hence the semicolon at the end of the first line The word hello on this line is called an identifier Identifiers are names given to various things to be discussed below they must start with a letter and they may contain letters and digits Upper and lower case letters in an identifier are considered equivalent but some compilers may insist that you only use lower case letters only this is not the case for the compiler at the Atrium The body of the program is in lines 2 4 Between the key words begin and end the action to be taken by the program is described there is only a single statement here given on line 3 The word writeln indicates that the program should write to the output file the screen and in parentheses between single quotes the text to be written is given note that both quote sings are r
119. ed only once by the editor say vi in the second window and after each correction the changes should be written out to the file using the vi command w without quitting the editor and then moving to the first window the program should be compiled again Between each compilation it is sufficient to make the corrections suggested only by one or two error messages it is usually best to act on the first error message since a single error may generate a number of error messages When there are no more error messages one may quit the editor by using the vi command q for this rather than wq since at this point presumably there are no new changes to be written out to the file 40 HI PASCAL 9 Simple Pascal Programs We are going to explore the Pascal programming language by considering a some what more complicated program 1 program example2 output 2 var num integer 3 begin 4 num 15 5 writeln The number is num 1 6 end This program is still quite useless from a practical point of view All it does after compiling and running it is to write the message The number is 15 on the screen A new feature in this program is the declaration contained on line 2 this line says that the identifier num denotes a variable of the type integer Integers are positive or negative whole numbers within a certain range the range depends on the particular Pascal implementation The Pascal compiler at the Atrium allows i
120. ed to make some corrections you can go back to command mode by pressing the escape key If your keyboard does not have an escape key you can achieve the same effect by typing Ctl i e by holding down the control key and pressing Cursor movement The cursor is a little square that highlights a one character size portion of the key usually to indicate where the next keystroke will have its effect In command mode you can move the cursor by using the keys h to the left j downwards k upwards and 1 to the right The arrow keys to the right of the keyboard can usually be used in the same way but it is better to use the keys h 2 THE VI TEXT EDITOR 13 j k 1 especially if you are a good typist since by taking away your hand from the main part of the keyboard you will lose time Also the arrow keys do not always work Other ways to move the cursor is by typing w to the beginning of the next word b to go backwards by one word tx to the next occurrence of the character x on the same line and so on With many of the above commands you can use a number to perform the com mand repeatedly For example typing 2k moves the cursor two lines up typing 131 moves it 13 places to the right and typing 3b moves it three words back Basic commands Assuming you are in command mode to delete the character at the current cursor position type x to delete the whole line in the cursor position type dd To delete a word type dw To
121. emp 19 end 20 write The greatest common divisor of the above 21 writeln numbers equals b 1 22 end In lines 8 18 a and b are interchanged in case we have a gt b initially In line 10 the old value of a is stored in a variable called temp so that in line 12 this old value can be assigned to b note that the old value of a is destroyed in line 11 This modification of the program will not significantly improve its efficiency we included this version only as an illustration Problems 1 Trace through the execution of the two programs in this section when a the values a 422 and b 546 are entered at the keyboard b the values a 546 and b 422 are entered at the keyboard 2 In the following program two positive integers are entered at the keyboard and the program is supposed to print out first the larger number and then the smaller number That is if a happens to be larger than b the numbers need to be interchanged on lines 10 12 Fill in these missing lines Semicolons must be correctly placed 1 program example input output 2 vara b temp integer 3 begin 4 write Type a a must be a positive integer 5 readin a 6 write Type b b must be a positive integer 7 readln b 8 if a gt b then 15 FILE HANDLING IN PASCAL 57 9 begin 10 11 12 13 end 14 write The larger of the two numbers 15 writeln entered is b 0 16 write The smaller o
122. ent when printed depending on the style file used The third line specifies a magnification by a factor of 1 2 over the regular size which would be magnification magstep0 If the magnification is not specified magstep0 is assumed in the first example we did not specify the magnification and this is why the letters in the printout were so small In lines 5 and 7 the pair head and endhead of control sequences enclose the title of the passage These control sequences are specific to A 4S TEX the way this title was rendered is specific to AMS Preprint Style amsppt using another style it might have been rendered in say small capitals FERMAT S LAST THEOREM Note that the line breaks in the tex file have nothing to do with the line breaks in the way the text is typeset that is even though line 9 is very short the corresponding text in the typeset version appears normal Line breaks and spaces only generate spaces between words in the typeset text in fact two or more spaces in the text file appear in the typeset text as a single space between words The places for the line breaks are calculated by the tex program and if necessary the tex program will even break up with a hyphen a long word that does not quite fit at the end of the line On line 14 smc changes the type face to small capitals that A D is printed instead of a d note that A D would not look as good The braces and are used as delimiters and they do
123. eople may prefer to take note of the address and send email on some other occasion without using the automatic addressing feature provided by this anchor More about the types of link targets called URI s or Uniform Resource Identifiers also called URL s or Uniform Resource Locators can be found at http cie motor ru RFC 1630 index html In line 35 the tag lt BR gt with the attribute CLEAR given the value LEFT inserts a vertical space until the left margin is clear so that the text will continue underneath the picture The main text of the Web page begins at line 44 The paragraph ends on line 61 and the beginning of the new paragraph is indicated by the solitary tag lt P gt on line 62 Actually this is not a solitary tag the tags lt P gt and lt P gt form a pair the former indicating the beginning of a paragraph and the latter its end however the latter tag is usually omitted since the beginning of a new paragraph also signals the end of the preceding paragraph Most browsers including Netscape display the separation of two paragraphs by adding vertical space corresponding to a blank line In order to indent the text starting on line 44 two space characters added at the beginning of the line A space character has the code amp 160 note that the first semicolon is part of the code On line 63 the line break tag lt BR gt inserts additional vertical space The anchor on line 58 is of special interest The name of t
124. er 17 writeln 15 1990 18 writeln enter 9 15 1990 19 readln month day year 20 decide if the current year is a leapyear 21 if year mod 4 0 and year mod 100 lt gt 0 22 or year mod 400 0 23 then 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 20 DAY OF THE WEEK 75 leapyear true else leapyear false initialize the lengthofmonth array this will store the remainder of the number of days in each month divided by seven lengthofmonth 1 3 lengthofmonth 2 0 lengthofmonth 3 3 lengthofmonth 4 2 lengthofmonth 5 3 lengthofmonth 6 2 lengthofmonth 7 3 lengthofmonth 8 3 lengthofmonth 9 2 lengthofmonth 10 3 lengthofmonth 11 2 lengthofmonth 12 3 the current setting of February is only correct if the year is not a leap year this will be remedied if leapyear then lengthofmonth 2 1 now calculate how many days have elapsed in the year up to and including the current day actually multiples of seven will be ignored in this calculation daystocurrent day for i 1 to month 1 do daystocurrent daystocurrenttlengthofmonth i each year has 365 52 7 1 days and each leap year has 366 52 7 2 days hence the number of years before the current year is counted and the numbe
125. ere sent out can be saved in a directory Since each letter contains the addresses where it was sent at a later day it can be ascertained to whom a certain letter was sent out 23 Shell Scripts More on sending email Often one has to repeatedly execute a sequence of simple commands rather than having to type the same thing at the terminal on repeated occasions one can put these command in a file and execute the file as what is called a shell script As the first example we describe how to deal with a flaw in the way the sending of email was organized in the preceding section While all the information concerning an email letter such as the content of the letter who it was sent to what the specified subject was was contained in the letter itself everything will go wrong if after carefully writing the letter one forgets to send it out In fact for a person liable to this kind of forgetfulness it will be impossible to tell weeks later whether the last crucial step of sending out the letter was carried out One way to deal with this situation is never to send out a letter by typing the appropriate mail command directly Instead one can create the following file called email bin sh mail v cat gt dev null lt 1 cat HOME marks sentmark gt gt 1 4 date gt gt 1 w Ne The first step is to make this file executable by typing 16In Linux the shell script 1 bin sh 2 mail vI lt 1 3 cat HOME
126. etter has scrolled down all the way the mail prompt will reappear if it has not then you can usually see the sign More highlighted if your window has a white background then the highlighted word will probably appear written in black into a little black rectangle If you want to save this letter under the file name letter msmith 5 you can type amp s 2 letter msmith 5 If there is no file by this name it will be created if there is a file by this name letter 2 will be appended to the end of this file You probably want to save all your letters in the directory mail_received cre ated for this purpose If you do not remember whether you are in this directory you can find it out by typing amp pwd Here amp is the mail prompt written by the computer and you only type the rest The exclamation point is the so called shell escape character shell is the regular environment where you type Unix commands That is after typing you tem porarily leave the mail environment and you can type any Unix command We met the command pwd above it stands for print working directory and it will tell you in which directory you are If you are not where you want to be you should exit the mail program by typing x change to the directory you want to be in and then reenter the mail program again by typing mail After this you can save the letter in question You can delete letter 2 by typing amp d2 you can delete more than one
127. etter to be understood than to appear knowledgeable Secret Web pages In order to view a file with Netscape you need to know the name of the file So if you put a file called for_joe3782 in your public_html directory and tell this file name only to your friend Joe no one else can read this file without somehow first finding out its name This works because the permission code of the directory public_html is 744 that is drwx x the d indicates that public_html is a directory the rest is its permission code so the general public has only permission to change to this directory and has no permission to list its content Of course as usual the file for_joe3782 must have permission code 611 You can think of the number 3728 as a PIN number Personal Identification Number used by bank cards to protect your money at ATMs Auto matic Teller Machines 7 Empowering Netscape There are various ways to make Netscape work for you better We will give some examples 8This phrase is commonly used by automobile manufacturers when rating the fuel consumption of a vehicle They might say something like a car rates 35 miles per gallon highway and 25 miles per gallon city but your mileage may vary depending on driving conditions 30 Il THE WEB Bookmarks on the Web Instead of creating the directory bookmarks dir in the netscape directory as described toward the end of Section 4 you can create it for example in your public_htm
128. exponent in export shell command 97 124 128 extended Euclidean algo rithm see Euclidean algo rithm extended fc 16 FCEDIT see shell variable FCEDIT Fermat s Last Theorem 82 Web site to read about 83 Fermat Pierre 82 Last Theorem of see Fermat s Last Theorem fg 125 file 8 ASCII 8 binary 8 compression see com pression of data executable 18 GIF 26 32 33 handling in Pascal 57 59 hidden 21 88 97 JPEG 32 33 name extension 37 unique in shell scripts 103 wild card in 119 wildcard in 12 owner of 17 readable 18 text 8 type text in Pascal see Pascal key word text writable 18 file Unix command 8 INDEX find 120 for see Pascal for state ment in foreground running jobs in the 20 FORTRAN 36 Free Software Foundation 7 38 Web site of 38 FreeBSD 6 Website of 6 Fundamental Theorem of Arithmetic see arithmetic Fundamental Theorem of Gauss Karl Friedrich 67 GCD see greatest common divisor geekspeak 29 ghostview PostScript viewer 30 GIF file see file GIF GNU 38 GNU Pascal differences in behavior from SUN Pascal 70 Graphical User Interface see interface graphical user graphical user interface 19 greatest common divisor 52 Gregorian calendar see cal endar Gregorian Gregory XIII Pope 76 grep 105 v option 112 GUI see graphical user inter face see interface graphical user gunzip 32 gzip 32 head see TEX head heade
129. f bottomless garbage can whatever is put in it just disappears Unix has two main kind of outputs standard output and standard error output The two kind of outputs are usually indistinguishable from each other since both are simply written to the screen Error messages of Unix commands are usually written to the standard error output For example if there is no file called junknetscape the command rm junknetscape writes the following message to the screen rm cannot remove junknetscape No such file or directory writes on the screen in actual fact to the standard error output Such a message would be confusing when running the above shell script The command rm junknetscape gt amp dev null writes nothing onto the screen since the standard error output is discarded redi rected to dev null The symbol gt is used the redirect the standard output and the one gt amp to redirect the standard error output Unix also has a standard input the standard input is usually what is typed at the keyboard Line 4 creates an empty file called junknetscape and lines 5 11 is a here document described in p 95 using the editor ed to edit the file junknetscape There we used the percent symbol to indicate the beginning and the end of the here document here we used the string heremark in lines 5 and 11 instead any string can be used but the percent sign is often favored since it usually does not have other uses we could h
130. f the Week Next we are going to consider a somewhat more complex program that will cal culate the day of the week give when given a date such as 3 17 1997 20 DAY OF THE WEEK 73 meaning March 17 1997 In the declaration part of the program we use the concept of an array The declaration given below in line 12 is as follows lengthofmonth array 1 12 of integer The identifier lengthofmonth here describes the data having data type array 1 12 of integer This means that there are 12 locations denoted as lengthofmonth 1 lengthofmonth 2 lengthofmonth 3 lengthofmonth 12 allocated to store data of the type integer These will be used to indicate the number of days in each of the month January through December in actual fact since multiples of seven can be neglected in calculating the day of the week instead of 31 for January we will store 3 instead of 28 for February we will store 0 and so on The char data type has not been used before this is used to store characters i e letters numbers and some other symbols Line 11 contain the following declaration dayofweek packed array 1 9 of char This reserves 9 locations of the data type char called dayofweek 1 dayofweek 2 dayofweek 3 dayofweek 9 These will be used to store the letters in the name of the day of the week Monday Tuesday to be printed out The meaning of the word packed in the declaration is that characters normally
131. f the two numbers 17 writeln entered is a 0 18 end 15 File Handling in Pascal We are going to show how to rewrite the Pascal program for the Euclidean al gorithm in a way that the input is taken from a file and the output is written to a file Only slight modifications are needed in the first program presented in the preceding section on p 55 The following program reads two positive integers from the file called infile and prints the result into the file called outfile Since this program is very much like the above mentioned program carrying out the Euclidean algorithm we will explain only these modifications after the program 1 program euclid infile outfile 2 vara b temp integer 3 infile outfile text 4 begin 5 reset infile 6 read infile a 7 read infile b 8 while a lt gt 0 do 9 begin 10 temp a 11 a b mod a 12 b temp 13 end 14 rewrite outfile 15 write outfile The greatest common divisor 16 write outfile of the above numbers 17 writeln outfile equals b 1 19 end In line 1 of this program the filenames infile and outfile are mentioned these are files where the input will be read from and the output will be written to respectively These filenames were chosen arbitrarily The filenames input and output are no longer used these latter names are reserved filenames input refers to the standard input usually the terminal keyboard and output re
132. f your home directory is home jsmith then you can view the above file by going to a Netscape window clicking on File then on Open Location and then typing file home jsmith html_files Alternatively you can create the following shell script called viewhtm1 as follows 24 MORE SHELL SCRIPTS 101 bin sh NN file HOME html_files 1 rm f junknetscape gt amp dev null touch junknetscape ed junknetscape lt lt heremark Oa netscape remote openURL NN new window wW q heremark junknetscape 13 xrm f junknetscape Pe FOWMO AN OA OTRFPWNEF e N Assuming that Netscape is already running you can run this script by typing viewhtml example html on the command line so as to view the above file What makes the above script complicated is that the command netscape remote gt openURL file HOME html_files example html new window here we broke up the command in two lines as explained on p 34 does not work since the netscape command does not understand the shell variable HOME instead one needs to specify the full path as in the command netscape remote gt openURL file home jsmith html_files example html new window What the above shell script does is to use the text editor ed to write the latter command above into the file junknetscape and then run the command in this file A filename such as junknetscape is used deliberately so as to avoid conflicts with
133. fers to the standard output 58 IV APPLICATIONS OF PASCAL usually the terminal display screen However the present program does not take input from the keyboard and it does not write to the terminal display screen In line 3 the files infile and outfile are declared to be text files more precisely they are declared to be a variable of type text That is the key word var on line 2 introduces the variables to be declared and lines 2 and 3 contain the names of these variables a b temp are declared to be of type integer on line 2 and infile and outfile are declared to be of type text on line 3 The statement reset infile in line 5 prepares the file infile for reading it is necessary to include this statement before the first read or readln statement referring to this file Its actual role is to make sure that the file is going to be read from its beginning a file to be read must be initialized i e it must be clarified from where it should be read in the same way as an integer variable must be initialized i e be given a value In line 6 the statement read infile a will read an item from the file called infile and makes this item to be the value the variable a The variable a having been declared to be of type integer the item to be read must be an integer Similarly the statement in line 7 reads the next item from the file infile Items in text files must be separated by one or more spaces or end of line characters That is
134. files compressed by gzip is available free for Unix systems and it is included with most Linux distributions You can compress your index html file by typing gzip index html The compressed file will be called index html gz while the index html file itself will be deleted In general gzip will attach gz to the filename to name the compressed file You can uncompress the file index html gz to get back the original file index html by typing gunzip index html Note that nothing is gained by compressing the same file twice The purpose of compressing files is to save disk storage space and even more importantly to save time needed for transmission of files especially through slow telephone lines You can put a compressed copy of your index html file in the public_html directory for faster retrieval of your Web page but note that you ought to retain a copy of the file index html as well since most browsers are not enabled to read compressed files As gzip deletes the original copy of the files you need to make special arrangements to retain a copy This is easy to do For example while working in the directory public_html you can accomplish this as follows cp p index html index html_temp gzip index html chmod 611 index html gz mv index html_temp index html Here the command cp p i e the p option of the command cp is used to copy a file while preserving its attributes such as permission codes the time of the creation
135. follows The list of statements is exe cuted and then the condition is tested If it is found that the condition is false the list of statements is executed again this is repeated until it is found that the con dition is true when the execution continues on the next line The repeat statement is also a loop statement In the present program the loop in line 7 is entered with a being false then in line 8 b is set to be the negation of a the operator not denotes logical negation In line 9 the current values of a and b are printed out the second item in the writeln statement prints an appropriate number of spaces for good alignment of the printed table The width 1 specified here results in printing T or F false for the values of a and b if the width were specified to be 5 True and False would be printed In line 10 the value of a is changed to be false so the second time the loop in line 7 is entered with a false In line 10 a is changed to be true and in line 11 the loop is exited since the condition is satisfied The following program prints out the truth table of conjunction 1 program example output 2 vara b result boolean 13This behavior is observed with the GNU Pascal Compiler gpc Sun Pascal behaves differently In Sun Pascal TRUE and FALSE are printed The International Standards Organisation ISO Pascal Report supports the interpretation given by GNU Pascal see Kathleen Jensen and Niklaus Wirth Pascal User
136. for this reason The correction is simple however Instead of making changes similar to the ones we made in the script viewhtml1 above p 111 to specify a path for the file junknetscape we can simply add the line cd HOME tmp 114 V MISCELLANEA before line 3 in the script viewhtml0 This will ensure that the temporary file junknetscape will be created in the directory HOME tmp Note that this directory change is effective only inside the shell script After quitting the shell script one will be back in the same directory where the shell script was invoked Going to a Web site given in a file The next script will go to a Web site given listed in the file given in the argument Calling this script netfread and assuming that the file tt website in the present wording directory contains the line http www egr msu edu the Web site of Michigan State University College of Engineering the command netfread website will open a new Netscape window whether or not Netscape is already running and go to the above site This script might be useful if a friends sends you a Web address in an email You can copy the address to a temporary file and use the script to access the site 1 bin sh 2 if test s 1 3 then 4 echo go to URL given in file listed as argument 5 exit 0 6 fi 7 if test f 1 8 then 9 echo file 1 does not exist 10 exit 1 11 fi 12 rm f HOME tmp junknetscape 2 gt dev null e w
137. ginal article and to my letter You can also go directly to the The Times Internet Edition to read the original article first then come back here to follow the links to the discussion and to my letter Last updated Wed Jul 22 10 06 03 EDT 1998 among this is the option HREF which introduces a hyperlink or hyper reference The form of an anchor with a hyperlink is lt A HREF link target gt anchor tert lt A gt The link target is the location of the Web page to be transferred to the anchor text is the text that is actually displayed on the page that is on which one needs to click in order to get the target of the link For example in the anchor given in lines 24 25 if one clicks on the displayed text Brooklyn College then one is transferred to the Web site of Brooklyn College which is located at http www brooklyn cuny edu Another type of anchor is given in lines 29 30 By clicking on the anchor text 28 Il THE WEB mate sci brooklyn cuny edu a window is opened in which one can type a letter to be emailed that is sent by electronic mail more about electronic mail later in Section 22 on p 86 The link target mailto mate sci brooklyn cuny edu contains the electronic mail address that the letter should be sent to Note that the link target itself is not displayed what is displayed is the anchor text which happens to be very similar the reason to display the electronic mail address in the anchor text is that some p
138. gnu ai mit edu In the above line we used the s option to indicate that we want the compiler only to accept standard Pascal this will be helpful when you want to port i e move to an environment different from the Sun computers at the Atrium your programs since no extensions unknown to some Pascal compilers will be accepted Actually the real world is more complicated than described here and there are different levels of compliance with standard Pascal To find out more you may want to read the on line manual pages of the Pascal compiler by typing man pc However Unix on line manual pages are notoriously hard to read so we do not recommend you to do this unless you are really dedicated To run the compiled program you simply have to type its name on the command line prefixed by the symbol first_program comp If everything was done correctly you should get the output Hello world On some systems the command first_program comp may work equally well This is an issue of system configuration and security that will be discussed in Section 23 on p 98 in the Subsection The present working directory in the search path Next we will outline how the above program works First note that everything in the above program is written in lower case except the letter H in the phrase Hello world which is quoted i e put between single quotation marks Certain words in the program are key words i e reserved words that have specifi
139. hange the input control sequence will make the TFXprogram look for the file somefile tex in all the places it used to look for it but now it will also look for it in the directory texinputs in your home directory 22 Electronic Mail Electronic mail is sometimes called email more often it is called e mail We are convinced by Donald Knuth s essay Email let s drop the hyphen which can be found at http www cs staff Stanford EDU knuth email html that the former version should be used There are various mail interfaces to Unix such as pine but these are not installed on every system it is available at the Atrium and you are welcome to find out about if interested Here we will explain how to use Unix mail itself without such easy user interface Reading email Reading email is simple First it is desirable to create a direc tory such as mail_received where you want to save the letters you receive The system usually notifies you when you have email In any case you can find out whether you have mail by typing mail here is the prompt given by the computer if you have no mail the computer will answer by something like No mail for jsmith where jsmith stands for the login name of the person logged in to the computer If you have mail the computer will list the letters received numbering them as 1 2 14Unix often has different versions of the mail programs If you do not get the behavior described below tr
140. he cursor moves down to the next place after the colon The computer waits for you to enter a command on the bottom line it is said to be in command line mode After entering the command and pressing pressing the enter key the command in question will be executed and the editor will return to command mode Typical commands are set nu which will put line numbers at the beginning of each line These lines will not be part of the file being created the file itself will not be changed the line numbers are useful in a long file for certain editing commands The line numbers can be removed by typing set nonu Typing 716 will move the cursor to line 16 The command 4 7d will delete lines 4 7 Typing 24 7 will join lines 4 7 into a single line Typing 4 7s string1 string2 g replaces each occurrence of the characters string with the characters string2 in lines 4 7 the letter s after the range 4 7 stands for substitute meaning that the second string gets substituted for the first one In fact this command is called the substitute command of vi Here g stands for global Typing the same thing without g i e entering 4 7s string1 string2 will replace only the first occurrence of string1 in each of the lines 4 7 For example the command 4 7s exit exists will change the first occurrence of the word exit to exists in each of the lines in the range of lines 4 7 while the command 12s there is there are g will change all
141. he link target is too long to fit in a single line of the window of the text editor For this reason the text editor wraps this line so that it can be conveniently viewed but from a logical view point this is a single line since it contains no line feed character Line feed character must not be included since the name of the link target must be reproduced exactly As a point of fact Netscape ignores line feed characters in the name of the link target Hence line 58 could have been broken up into three lines without changing the appearance of the Web page 44 http www the times co uk news pa 45 ges sti 97 04 20 stiinns 46 nd01001 htm1 1007000 we included line numbers these are not part of the text in this case the line numbers of the successive lines have to be increased accordingly However this appears to be a feature of Netscape and the documentation of HTML does not seem to explicitly state that such line breaks are allowed For this reason such line breaks should be avoided since they may cause trouble for some browsers other than Netscape We will not touch upon the more complicated features of HTML there are many books available on HTML One can also learn more about HTML by consulting various Web sites The Web site of the World Wide Web Consortium 7One needs to be precise here about what is quoted hence one semicolon inside and one outside the quotation marks 7 EMPOWERING NETSCAPE 29 http www w3 org i
142. he single line Letter sent on date This was the missing step we referred to above and after completing this step the shell script email will work properly It can now be seen that the effect of the command cat in line 3 is to write the line Letter sent on date at the end of the file cmuserd Finally in line 4 the command date generates the current time and date and it writes it at the end of the argument referred to as 1 i e the file cmuserd To sum up the above shell script will mail out the file cmuser and append information at the end about the act of mailing it out In the end the file cmuser5 described in the preceding section will look something like this m t cmuser math some school edu s Your suggestion Dear Charley Sat Jun 21 21 06 51 EDT 1997 I think I can make your suggestion work I have to think about it a little more however Regards OMAN OAF WD J F Smith 23 SHELL SCRIPTS 93 10 jsmith math myschool edu 11 http www math myschool edu jsmith 12 13 Letter sent to Charles K User 14 Letter sent out on date 15 Sat Jun 21 21 19 23 EDT 1997 As can be seen lines 14 and 15 were added at the end of the file by the shell script email that we were discussing It might look better if lines 14 and 15 were written in a single line rather than in two lines as they are now in this case the word date and the colon afterwards should also be omitted To accomplish this one needs to c
143. hen the execution of the program arrives at this statement it will wait for input to be typed at the keyboard the window in which the program is running must be the active window i e the mouse pointer must be located in this window It will accept input until an end of line character is typed and the characters typed before the end of line character will be used to form the content of the variable num1 indicated in parenthesis in the readin statement in question The sequence of characters typed must form a positive or negative integer since the variable num1 was declared to be of the type integer Without the write statement on line 4 the person running this program would not know why the program waits upon arriving at line 5 in fact she would not even know that the program arrived at line 5 she would only notice that the program is not doing anything as if it had stopped As the write statement prints the message Enter the first number on the screen here we indicated the space characters printed on the screen by u to call attention to the the fact that a space character is printed at the end of the line normally we will not indicate space characters this way since their presence is clear from the space left between words After this the readin statement on line 5 will wait for a number to be typed If the number 153 is typed and return key is pressed the variable num1 will be assigned the value 153 and the screen will look
144. hese process id s will be the empty string so lines 6 8 of the conditional command in lines 3 21 will be executed In case Netscape is running the list will not be the empty string so lines 10 20 will be executed Note that we named the above script viewhmt11 Whatever else we might have named it instead no name containing the string netscape is allowed Otherwise the process id of the script itself would be picked up in line 4 so the test in lines 3 4 would always return false If Netscape crashed or froze the process associated with Netscape would probably be still around so the test in lines 3 4 would return false however Netscape might not be in a position to accept any commands such as the command given to in line 19 so the only option in this case would be to kill Netscape see pp 104 and 109 A new feature of this script is the place the temporary files in a special directory namely HOME tmp that is instead of junknetscape we used the temporary file HOME tmp junknetscape 24 MORE SHELL SCRIPTS 113 It is important to make sure that this directory exists if it does not it needs to be created and has read write and execute permissions by the user In fact for security reasons this directory should have no other permissions that is the permission code of this directory should be 700 see p 18 in Section 3 The main reason for this is the so called symlink attack cf http www egr msu edu archives public
145. his in the present example would be users jsmith and normally the login name of the user in question would be jsmith You can find out if this is indeed the case by typing whoami the expected reply being jsmith Creating directories You can create a new directory by the mkdir command For example if you are in the directory users1 jsmith euclid then the command mkdir eucl_algorithm will create a subdirectory called eucl_algorithm provided no directory or file by this name exists in the directory users1 jsmith euclid if such a file or directory already exists the computer will come back with a message explaining why the new directory could not be created If you change your mind and do not want the directory after all you can remove it by typing rmdir eucl_algorithm as long as the directory is empty i e no files or directories have been placed into the directory More on files You can remove a file called sec2 by typing rm sec2 We mentioned above how to remove an empty directory by using the rmdir com mand If the directory is not empty i e if it contains files or other directories then the command rm r needs to be used For example the command rm r eucl_algorithm removes the directory eucl_algorithm along with all the files and directories con tained in it This is a dangerous command since before you use it you must be sure you want to discard all these files and directories whereas the command rmdir is
146. his is T X The letters in the display will perhaps be smaller than desired we will explain later what to do about this This display window may be left open If changes are made in the file first tex and the file is repeatedly typeset by typing tex first then the display can be updated simply by clicking in the display window with the left mouse button To print the file one can type dvips first o This will produce a file called first ps dvips stands for dvi to PostScript that is it translates the dvi file first dvi to PostScript file called first ps PostScript is a page definition language of Adobe Corporation the PostScript file can be sent directly to the printer by typing 80 V MISCELLANEA lpr first ps This will send the file to the default printer that is the computer will guess which printer you want to use If you want to use a specific printer you need to know the name of the printer assume for example that the name of the printer you want is hwp Then you can specify that you want the printout on this printer by typing lpr Phwp first ps Along with your printout header page is usually printed This is the first page and it contains information about the job you are printing but it is not part of what you want to be printed If you are the only one using the printer at the given time your printout will not be mixed up with other people s printouts So to save paper you can avoid printing the header p
147. hout having at every time to explicitly say whether we refer to the program or to the printout First observe that the widths indicated on the inserted writeln statements are needed to ensure the proper alignment of the printout The width specification sum 3 ensures that the width of three characters are reserved for printing the value of sum the reserved space of three characters are used to print the the number right justified i e as far to the right as allowed by the reserved space and the spaces not used up by digits or by a possible minus sign are filled with spaces Thus the printed values of sum in lines 33 and 33 of the printout are properly aligned Note that the inserted writeln statements do not change the action of the program at all except for the extra lines of printout obtained Thus the printout gives a fairly complete trace of the program First note that line 21 of the printout would have been printed by the original program and the number 6 at the end of the line was in fact typed by the user and not printed by the program As line 22 tells us after line 7 of the program the value of 7 is 1 so the condition in line 8 is satisfied Hence the loop in lines 8 12 is entered As line 25 of the printout shows the first time line 11 is reached the value of i is 2 the condition in line 8 is again satisfied so the execution continues in line 9 Lines 28 31 34 37 show the successive values of i in line 11 since this va
148. ight quote signs The period on line 4 indicates the end of the whole program The various parts of the program are kept apart by the use of separators These 8 INTRODUCTION TO PASCAL 39 are spaces and line feed obtained when pressing the return key characters For example the space between program and hello is a separator Without it the key word program would not be recognized the word programhello would be taken to be an identifier One needs at least one separator to keep different parts of the program apart but the use of more than one separator is also allowed For example there are three separators after the word begin in line 2 one end of line character and two space characters Compilers usually accept the tab character but the Pascal standard specified by the ISO International Standards Organisation does not mention the tab character as a separator The above program could also have been written as program hello output begin writeln Hello world end we omitted the line number here which in any case is never a part of the file containing the program Indeed the required separators are present in this version of the program and the compiler will not complain However the first version is easier to read for people and so it is preferable In particular indentation is used to make it easier for people to recognize various parts of the program Correcting errors in Pascal programs Errors in Pascal programs com
149. ile cdbase has to be put into the directory HOME 1ib sources and it has to be changed so that its content should be mv sc junk scl junk cd usr lib texmf texmf tex amstex base This source script will work in cooperation with the following script called return placed also in the directory HOME 1ib sources with the following content cd cat sci junk It is important to note that the quote signs here are left quote sings using right quotes will not work The meaning of the command displayed is as follows execute the command between the left quotes and take the result of this execution as the argument of the command cd Now we can explain how all this scheme works When typing sc cdbase the present working directory is saved into the file HOME 1ib sources sc junk Assume this directory is say usr lib X11 The second command in the alias defining sc separated from the first one with a semicolon changes to the directory cd HOME 1ib sources and the third command runs sources the file listed on the command line cdbase at present this file must be present in the above directory The first action of sourcing the file cdbase is executing the first command in this file i e moving the file sc junk to sc1 junk and the second action is changing to the directory with the long name described in the second line If after doing some work one wants to return to the directory where one was before changing directories one
150. ill discuss a script that can be used to kill all Netscape processes We will chose the name killns for this script that is the script can be invoked by typing killns without arguments We will comment on the name killns below Here is the script in the next subsection we will discuss how a much shorter script can be written to do the same task 1 bin sh ps x grep netscape gt junkkill0 cat junkkillo awk print 1 junkkill0 gt junkkill cat junkkill ed junkkill lt lt 2 gt dev null an FF WD 106 V MISCELLANEA 7 Oa 8 kill s 9 9 10 1 1s 11 w 12 q 13 14 cat junkkill 15 junkkill 2 gt dev null 16 rm rf HOME netscape cache 17 rm f HOME netscape lock 18 rm f junkkill junkkill0 First notice that the filenames junkkill and junkkill0 are unique names for temporary files as discussed above see p 103 The pound sign is the shell comment character Its role in line 1 has already been discussed cf p 91 Its role at the beginning of lines 3 5 and 14 is to make these lines ignored These lines are not needed in the shell script but they are useful for debugging that is when writing the script these lines are initially not commented out that is the pound sign is not put at the beginnings of these lines initially since when writing the program it is useful to know what is written in the files junkkil1 and junkkill 0 For
151. ines Some of the above ways to connect to a remote machine can be used even if the local machine is not a Unix machine Telnet is perhaps to most widely understood protocol to do this The ways different operating systems invoke telnet depends on the configuration of the local machine one can often use Netscape to start up telnet To do this first click with the left mouse button on the word File in the Netscape windows this will open a small window with a number of choices By clicking with the left mouse button on the phrase Open Location among these choices another window will open see p 20 27 REMOTE ACCESS 129 After positioning the mouse pointer in this window one can type the command to start telnet telnet machinename its brooklyn cuny edu Telnet is probably the most widely supported protocol on non Unix machines but one may also try using other protocols E g using Netscape as above instead of telnet one may be able to connect to a remote machine by typing rlogin machinename its brooklyn cuny edu Using rsh instead of rlogin will probably not work In the way described above one may be able to connect to the Atrium from the computers provided for Web browsing in the New York Public Library by using telnet or perhaps rlogin When logging in to a computer from a public place such as a library you must be very careful to also log out It is very easy to inadvertently click on a large window that will hide the login
152. ing email 93 here document 95 source 121 124 search path 97 secret Web pages see Web pages secret selector in case statement in Pascal see Pascal case statement selector in semantics 44 semicolon in Pascal programs see Pascal semicolon in separator in Pascal see Pas cal separator in Shannon Claude E 31 shell 7 alias see alias shell bash see shell Bourne again Bourne 91 conditional command in 111 if command in 111 Bourne again 91 C 91 comment character 91 106 INDEX escape character 15 87 Korn 91 script see script shell variable 92 FCEDIT 17 HOME 92 PATH 97 shift key see key shift sl see TX sl slanted in TeX see TFX slanted in slash 9 small capitals 83 smc see TEX smc Solaris 6 source 122 source program 39 91 source script see script source standard input 57 102 standard output 57 102 statement in Pascal see Pas cal statement in stored program computer 40 stuck window see window locked up subdirectory see directory sub subscript in TFX see TEX subscript in substitute command of ed 108 of vi 14 Sun Microsystems 6 SUN Pascal differences in behavior from GNU Pascal 70 SunOS 6 superscript in TEX see TEX superscript in superuser 127 symlink attack see attack symlink syntax 44 141 lt tab gt tab character 110 tail Unix command 128 f option of 128 technical jargon online dic tionary of 29 telnet 128 1
153. ion has many solutions the simplest one is 3 2 4 2 5 2 par It is generally assumed that Fermat did not have a proof of his Last Theorem In the first place he never announced the general statement publicly but he repeatedly made public statements about the special cases n 3 and n 4 as late as 1659 Probably he found a mistake in his original proof and was able to prove only special cases He had no reason to retract a statement he never made in public Fermat s Last Theorem was finally established by Andrew J Wiles of Princeton University The history of Wiles s theorem with a in the first version is interesting and maybe should discussed in an extended version of this essay in 1994 You can read more about its history at centerline tt http www coe uncc edu cas flt htm1 bye The numbers on the left are line numbers and not part of the file Before we explain the main points about how to prepare the above file we include here the typeset version of the above text Fermat s Last Theorem Around 1637 the French lawyer and amateur mathematician Pierre de Fer mat 1601 1665 wrote on the margin of his copy of a book by Diophantus the Greek mathematician of the third century A D a sentence that can be rendered with modern mathematical notation as follows There are no positive integers n gt 2 a b and c such that a b c 21 MATHEMATICAL TYPESETTING 83 hol
154. iority rules for arithmetic expression in Pascal see Pascal arithmetic expression in priority rules for process in Unix see Unix process process id 103 profile file 97 program maintenance of 50 portability of 50 running 125 running in background 79 124 running in foreground 124 stopped 125 140 INDEX terminating 80 125 program see Pascal key word program programming errors logic 39 syntax 39 programming languages 36 prompt shell 7 primary 34 secondary 34 propositional logic see logic propositional propositional variable see variable propositional pwd 10 quitting Netscape see Netscape quitting quotes in TRX see TEX quotes in read to read from a file see Pascal reading from a file readin see Pascal key word readin real type in Pascal see Pas cal real type in Red Hat Linux distributor 127 129 Register The Web site of 5 remote access 126 129 remote computer connections from the New York Pulic Li brary see New York Public Library remotely connecting to computers from repeat see Pascal repeat statement in repetitive statement see Pas cal loop in reset see Pascal key word reset return key see key return right justified see justified right rlogin 128 rm 11 f option of 22 i option of 22 r option of 11 rf options of 22 rmdir 11 root directory see directory root Rowe James 5 rsh 126 129 script shell 90 98 for writ
155. ks html in the directory netscape the latter is normally located directly in you home directory Note that the directory netscape is a so called hidden file see p 88 so to list it you need to type 1s a rather than 1s What you can do is to make a directory called bookmarks dir in the directory netscape and copy the bookmarks htm1 file into the former directory Working in the directory netscape you would do this by typing say cp bookmarks html bookmarks dir bookmarks5 html if say you are doing this the fifth time so the files boommarks1 htm1 through boom marks4 html in the directory bookmarks dir already exits After doing this you can delete all except perhaps a few most frequently used items from your book marks You should do this by using the bookmarks button in Netscape rather than deleting lines from the bookmarks html file since if you do the latter Netscape will complain The fact that Netscape complains can be considered a flaw in Netscape at best it is a Uniz unfriendly feature in Netscape Ideally Netscape should accept any changes made in its bookmarks htm1 file or in its other configuration files if these changes are correctly made and should not force the user to use Netscape buttons to make configuration changes To go to a site stored in the just created bookmarks5 htm1 file you should proceed as if you were going to a Web side as described above but after clicking on the Open Location button you sho
156. l directory After assigning the permission codes as described Section 5 711 for directories and 644 for files you can then look at bookmarks in question by typing http your_web_site bookmarks dir bookmarks5 htm1 in the Open Location window of Netscape if you called the file containing the book marks bookmarks5 html as at the end of Section 4 This solution will only work on a computer where you have an accessible web page In this example the phrase your_web_site should be replaced with the actual address of your Web page For example if your login name is cmuser and you have a working Web page at the Atrium you can access the above bookmarks by typing http acc6 its brooklyn cuny edu cmuser bookmarks dir boo kmarks5 html the above line needs to be typed in a single line since it is too long to print it as a single line in these notes we scrolled its end over into the next line You should have no problem with typing the line in the Open Location window without breaking it up Here acc6 its brooklyn cuny edu is the address of the Web server at the Atrium Computer Laboratory of Brooklyn College The advantage of this solution is that you can have remote access to your bookmarks So will everyone else who knows where to look to prevent this instead of naming the directory bookmarks dir you may give it some unlikely name such as bookmarks4796 dir Note that unauthorized users cannot easily find out the name of this directory si
157. l numbers is called the extended Euclidean algorithm Problem 1 Using the extended Euclidean algorithm find the greatest common divisors of the following pairs of numbers and represent them as linear combinations of the given numbers a 14 and 25 b 384 and 488 c 645 and 242 d 122 and 48 e 735 and 141 f 452 and 984 17 PASCAL PROGRAM FOR GCD AS A LINEAR COMBINATION 61 17 Pascal Program for Finding the Representation the Greatest Common Divisor as a Linear Combination In order to write a Pascal program to find the representation of the greatest com mon divisor as a linear combination we have to carry out the calculations described in the preceding section in a completely symbolic way We recall that in the example described there we showed how the equation 24 422 9 546 7 can be obtained from the equations 124 422 1 546 1 50 422 4 6546 3 In this derivation we also used the equation 24 124 50 2 For the symbolic discussion write aj 422 and b 524 the original numbers whose greatest common denominator is being taken at the step in the Euclidean algorithm we are considering we have a 50 b 124 The equation that q 2 is the quotient and r 24 is the remainder when 50 is divided in 124 can be written as 124 2 50 24 or as we rearranged it above 24 124 50 2 Symbolically this equation can be written as r b aq The equations 124 422 1 546 1
158. l1 see p 105 such as using the example given in p 107 10522 10532 That is disregarding the commented out line instead of lines 2 and 4 we could have written the following single line in the script killns ps x grep netscape awk print 1 cat gt junkkill The semantics meaning of the construction commandi command 110 V MISCELLANEA can be described as follows command1 is executed with the argument or arguments that result as the output of command2 That is the output of command may contain several fields separated by one or more separators Here separators can be spaces end of line characters or tab characters Fields are strings of characters not containing separators This construction is called command substitution in that the result of the execution of a command is substituted as an argument of another command To illustrate this construction consider the following example echo cat argfile where argfile is a file with the following content 1 2 3 lt tab gt 4 5uu6 Here lt tab gt stand for the tab character and as usual stands for the space char acter The echo command was discussed on p 97 What it does it simply to repeat its arguments to the standard output while evaluating shell variables In case of several arguments these arguments are separated by single spaces In the above command cat argfile send the content of argfile above to the standard ou
159. line 0 of the file for insertion That is line 8 of the script gets inserted after line 0 i e as a new line 1 or a new 3The Unix command pidof can be used to find out the process id of a process directly The command is available for example in Red Hat Linux but it is not available in Solaris 108 V MISCELLANEA first line of the file junkkill there is no line 0 line 0 is a way to refer to the beginning of a file The sole period in line 9 indicates the end of the inserted text that is the inserted text consists solely of line 9 of the script Line 10 edits the range 1 1s of the file by using the substitute command of ed this command works much the same way as the substitute command of vi see p 14 Here 1 of course refers to line 1 of the file and its last line 1 refers to the line before the last one Finally instead of 1 we wrote 1 the shell quote character is needed otherwise the dollar sign would be interpreted as introducing the value of a shell variable as in HOME being the value of the shell variable HOME The shell strips away this quote character and when the editor ed processes line 10 of the script it sees the range 1 1 rather than 1 1 The editing done in this range is the replace the string with the string here u indicates a space character usually we indicate a space character just by leaving a space for it but in the present case we need to write the symbol for the
160. line 30 will not fail Lines 45 47 and lines 48 49 use similar tricks 24 MORE SHELL SCRIPTS 119 Perl Many of the programs described above can be more written more elegantly in the computer language Perl See http www perl com or the book Larry Wall Tom Christiansen and Jon Orwant Programming Perl O Reilly amp Associates Inc Sebastopol CA http www oreilly com Previewing TFX files As explained in Section 21 if you have a T X file called whole tex you can typeset it with tex whole and preview it with say xdvi s thorough whole amp This will open a preview window in which the typeset file can be seen see p 79 If you change the file whole tex then you need to type the former command to typeset it again You do not however need to type the latter command again if you simply click on the preview window you can see the new version of the typeset file Things can go wrong however if the file whole tex takes long to typeset If you click on the preview window before the new version of the file whole dvi is written the preview window will display nothing useful It will probably display the lines DVI file corrupted This is because the old version of the file whole dvi has already been removed and the new version is being written Since the typesetting of a long TFX file can take as long as ten seconds this may be quite inconvenient The following shell script provides a simple workaround this problem
161. linux user 2000 March 000051 htm1 note that the above address should not be broken up and should have no spaces we had to break it up here since it does not fit in one line In the symlink attack temporary executable files created by user programs are replaced by malicious pro grams placed there by an attacker symlink is short for symbolic link To prevent this from happening no outsider should have permission to place anything into the above directory In earlier scripts we simply put temporary files into the present working directory the possibility of a symlink attack make these scripts less secure than the most recent script where a separate tmp directory is used for temporary files Another problems with the earlier scripts is that these scripts will fail if one tries to run them in a directory that lacks one of these permissions Otherwise there is very little need to comment on the rest of the script Line 6 removes Netscape s cache line 7 removes its lock file we want these commands to be silent so we send the standard error message to dev null so the command will not complain even if there is nothing to remove and line 8 starts up Netscape in the background All this is done in case Netscape has not already been running Lines 10 20 are much the same as lines 3 13 of the script viewhtml on p 101 The differences are that in the present script we used unique filenames see p 103 and put the temporary files in a speci
162. ll be to write Hello world on the screen Before we explain the meaning of the lines of this program we will describe how to run this program The first step is to create a file called say first_program p containing the above text It is traditional in Unix to end names of Pascal programs with p In DOS parlance p is called file name extension because in the old operating system DOS for personal computers the file name consists of a main part and a period followed by what is called a file name extension In Unix it is not correct to talk about file name extension simply Unix allows periods in file names and p is just the last part of the file name some Unix setups require that file names of Pascal program end this way others do not in DOS the required file name extension for Pascal programs is usually pas As a matter of good work organization it is better not to create the file first_program p in your home directory Instead you can make a new directory called say pascal_programs by typing mkdir pascal_programs on the command line and create the above file in this directory Recall that you do not type the at the beginning of the line it is the prompt provided by the computer to indicate that you may type a command If you already created the file first_program p in your home directory you can use the mv command described in the introductory section on Unix see p 11 in Section 1 to move it into the newly create
163. ller that the largest integer representable by the Pascal compiler at the Atrium and indeed if one runs the program with n 65535 the correct printout is obtained The sum of integers from 1 through 65535 equals 2147450880 Thus the above program should be only run with values n lt 65535 It is desirable to write the program in such a way that it will not run if a larger value of n is entered Otherwise the wrong result may inadvertently be accepted In fact if one runs the program with n 99000 the printout The sum of integers from 1 through 99000 equals 605582204 which is wrong but it may not be recognized as wrong upon a casual glance The correct answer is in fact 99 000 gt i 4 900 549 500 i 1 The following modification of the program prevents such errors from happening 1 program example5 input output 2 var i sum n integer 3 begin 4 write Type n n must be a positive integer 5 readin n 6 if n gt 65535 then 7 writeln n is too large 8 else 9 begin 10 ics i 11 sum 0 12 while i lt n do 13 begin 14 sum sum i 15 i i 1 16 end 17 write The sum of integers from 1 through 18 writeln n 1 equals sum 1 19 end 20 end The new feature this program is the if statement starting in line 6 In fact this statement takes up all of line 6 16 The syntax of the if statement can be described as 50 HI PASCAL if condition then s
164. llnsO returns a list of the process id s of the processes having netscape in their name as we mentioned above because of the left quotes around the command the the process id s are separated by spaces even though without the left quotes the command would return a list of process id s separated by end of line characters see p 110 However one processes having netscape in its name is the command grep netscape and the process id of this command is sometimes but not always re turned by line 3 in the script killnsO There this caused no trouble but here we want to find out whether Netscape itself is running In line 4 of the present script the grep command is used among others with the v option The command grep v string file selects those lines of file which do not contain string Thus in the command ps x grep netscape grep v grep ps x selects all processes one line of output for each process then the second member of the pipe grep netscape selects those lines in the output that contain the word netscape and the third member of the pipe grep v grep selects those lines among these that do not contain the word grep Thus the line corresponding to the process grep netscape is discarded and the lines that are kept are genuinely associated with Netscape In case Netscape is not running or rather in case there is no process other than grep netscape having netscape in its name the list of t
165. lue is less than or equal to 6 the value of n the condition in line 9 is satisfied and the loop is reentered Finally line 40 shows that the next time the value of 7 on line 11 is 7 the condition in line 9 is tested again and it is found that the condition is not satisfied since 7 lt 6 us false The loop is not reentered and the execution of the program continues in line 13 Line 41 indicates the values of sum and i right after the loop is exited Of course only the original version of the program continues in line 13 the modified tracing version of the program continues in line 12a But the tracing statements inserted in lines 7a 9a 10a 11a and 12a do not affect the working of the program except for the tracing printout obtained Finally line 42 shows the printout of the original version of the program produced in lines 13 and 14 11 LOOPS 47 As seen form the above trace the variable 1 is initially given the value 1 in line 6 and its value is incremented i e increased by 1 in line 11 on each execution of the loop that is assuming n 6 7 runs through the values 1 2 3 4 5 6 7 The variable sum is initially given the value 0 in line 7 and its value is increased by the current value of 7 in line 10 on each execution of the loop That is sum runs through the values 0 1 0 1 3 1 2 6 3 3 10 6 4 15 10 5 21 15 6 The last value of 7 is 7 but after 7 is given this value in line 11 the loop condition
166. lumn and then click on Applications among the subitems that appear In the middle of the window you will see a number of applications that Netscape can invoke For example PostScript might have the following entry 7 EMPOWERING NETSCAPE 31 Description Handled by If an entry like this is already present there is nothing to do If not you need to add it by clicking on the button New in the lower part of the window A window entitled Netscape Application will open up you will have to make the entries given in the right column Description Postscript Document MIMEType application postscript Suffixes ai eps ps In the lower part of the window under the major heading Handled By click on the diamond next to the word Application so as to highlight the diamond then enter the location of the ghostview program followed by a space and the string s First you need to find out the location of the ghostview program The best way do this is to type which ghostview This command will tell you the location of the program ghostview that is invoked when you type the command ghostview Alternatively you can also type whereis ghostview but the result is harder to interpret since whereis gives also other information e g the location of the online manual pages If the answer is usr X11R6 bin ghostview then you make the appropriate entry in the small highlighted area on the right Application usr X11R6 bin ghostview s Having enabled
167. mand line command substitution 110 comment character in shell see shell comment character comment in Pascal see Pas cal comment in comment in T X see TEX comment in common divisor 52 greatest see greatest common divisor compiler 37 INDEX compound statement in Pas cal see Pascal statement in compound compression of data 31 lossless 32 lossy 32 computer s information on the Web about using 20 language compiled 91 interpreted 91 conditional command in Bourne shell see Bourne shell con ditional command in statement in Pascal see Pascal statement in condi tional conjunction 70 const see Pascal key word const constant in Pascal see Pas cal constant in control key see key control control sequence in TEX see T X control sequence in control variable in Pascal see Pascal for statement control variable in Control for vi escape 12 Control c 80 125 Control z 125 cp 12 p option of 32 99 r option of 12 CR see carriage return character creating directories see direc tory creating cshrc file 121 Ctl see Control for vi escape Ctl c see Control c 133 Ctl z see Control z cursor 43 80 movement in vi see vi cursor movement in data compression see com pression of data data type in Pascal see Pas cal type in DEC 6 declaration in Pascal see Pascal declaration in default 26 41 80 filename for compiled Pascal programs see a out
168. mentioned above and start Netscape again However often when Netscape crashes the Netscape program process cf p 103 is still around and it must be dealt with it must be killed This is a somewhat more complicated issue an it is discussed on p 104 Clearing Netscape s cache Depending on the version of Netscape you are 22 Il THE WEB using it may not be very good about clearing its cache mentioned just before and a cache that is too cluttered may actually slow down Netscape From time to time you can clear the cache by typing the command rm rf cache in your netscape directory See the discussion below why this command is some what dangerous Here the command rm as we saw it above is used to remove files or directories option r says that directories should also be removed without this option directories are not removed the option f forces removal more about this below and the two options can be stated together as rf Finally stands for any file or directory in fact technically directories are also files so the above command removes all files or directories located in the directory cache Normally one does not need to use the f option with the rm command to force removal of files However especially for novice users the command rm is often a shell alias for the command rm i shell aliases are discussed on p 121 If so whenever you type rm on the command line actually the command rm i is execute
169. moves files and once you executed it it is too late to think that you really wanted to keep the file For this reason its meaning is often changed see the next secion for details The unalias command removes the alias from the rm command but it only does this for the duration of the shell script so no permanent change is made In case the command rm is not aliased the unalias command will send an error message to the standard error output see above since you do not want to see this error message the error message is discarded by the redirection 2 gt dev null In lines 3 6 the find command is invoked the backslash at the end of lines 3 5 quotes the newline character at the end of these lines to indicated that the command does not end with the end of these lines The find command starts its search in the current directory indicated by the period and searches this directory and all its subdirectories and their subdirectories the usual expression is to say that the command recursively searches the subdirectories for files whose name matches the pattern given after the option name the patterns are placed between single right quotes e g a out The o means or that is search for files whose name 25 SOURCE SCRIPTS 121 matches the pattern core or junk or junk or a out These files are unneeded and will be removed by the command the file core is usually left over by a crashing program see Section 15 and a out is the
170. n 6431 pts 13 00 00 00 netscape commun 6531 pts 12 00 00 00 sleep 6534 pts 12 00 00 00 ps The list is quite long in fact it may contain more than one hundred lines so we did not present the whole list the lines with a series of dots each represent a number of lines that we omitted In fact if you type the above command you will most likely not see the output properly because it will run past you in the output window two quickly before you can read it and you will only be able to see the last twenty of so lines of the output One way to deal with this problem is to pipe it through the more command 22This is a so called BSD style option where one types ps x rather than ps x This works in Linux Unfortunately different versions of Unix use different forms of the ps command in Solaris one needs to use ps A ps a or ps e you need to consult the online manual pages to find out the exact form needed in various forms of Unix You can get the online manual pages on the command ps by typing man ps see p 9 for man command 24 MORE SHELL SCRIPTS 105 ps x more To explain how this work we first have to discuss the more command Given an ascii file called say textfile you can view its content by typing more textfile you can also use an editor such as vi to view the content of this file Upon typing this command you can see the beginning part of the file textfile in fact exactly as much of it as fits your window
171. n or port the program Comments are very helpful in this respect The second feature is the declaration of a constant in line 10 In the earlier version the value of this constant was explicitly written in the condition that is now in line 15 In porting the program this constant may need to be changed it is much easier to find values that may need to be changed by looking through the constants in the declaration part of the program than to scan the whole program for values that need to be changed The declaration of the constant starts with the key word const the value of the constant must be given in the declaration using the equation sign rather than the assignment symbol The value of a constant cannot be changed in the program i e a constant must not appear on the left hand side of an assignment statement 52 IV APPLICATIONS OF PASCAL CHAPTER IV APPLICATIONS OF PASCAL A mathematical discussion of the Euclidean algorithm and its extension to rep resent the greatest common divisor of two numbers as a linear combination is given Pascal implementations of the algorithms presented are described and a proof of the Fundamental Theorem of Arithmetics asserting the unique prime factorization of integers is included Then Pascal programs are presented to print truth tables and to determine the date of the week in the Gregorian calendar 13 The Euclidean Algorithm The common divisors of two numbers are the numbers that are di
172. n property i e the existence of two different prime factorizations in the above example to be disproved is called the method of infinite descent It is a variant of mathematical induction Problems 1 You should be able to answer this question without doing any calculations in fact the numbers given are probably too big even for your calculator Given that you know that 7 324 472 493 949 4 057 012 961 706 13 2 285 806 141 970 012 665 670 538 and 4 057 012 961 706 13 312 077 920 131 3 decide whether 7 324 472 493 949 is divisible by 13 Give reasons the correct reason is just as important as the correct answer Do not waste your time by dividing 13 into 7 324 472 493 949 since the answer can be given much more quickly by reasoning 2 Using the second equation in Problem 1 determine the greatest common di visor 13 and 4 057 012 961 706 19 Truth Tables Pascal has propositional variables i e variables that can take values true and false and it also implement certain operations of propositional logic such as negation disjunction and conjunction One can use these features to create truth tables of propositional formulas In Pascal a propositional variable is declared to be of type boolean in recognition of the British mathematician George Boole who formalized propositional logic 1 program example9 output 2 var a result boolean 3 begin 4 writeln A not A
173. name if the file by the name filename exists To go around this problems a space is added in front of each string that is the strings s and 1 are compared here placed before the space character quotes the space character so the latter is interpreted as part of the string rather as separator If 1 is the string s that is if the command entered is netfread s then the command on line 4 simply writes the line go to the URL given in file as argument written on the screen and the command line 5 exits the shell script The argument 0 of the command exit means that the shell script will be terminated with the exit value 0 The exit value 0 means that the script terminated without error other exit values are used to indicate various error conditions that caused the termination of the script In line 7 the condition test f 1 116 V MISCELLANEA is true if the file named in the argument 1 exists and the exclamation point in the same line negates this condition That is if the file does not exist then line 9 reports this fact and line 10 makes the shell script terminate with exit value 1 we use this exit value since to run this script while the file in question does not exist should count as an error As before line 12 removes the file junknetscape if it exists and line 13 creates a new empty file by this name Lines 15 and 16 test if Netscape is already running the condition is true if Netscape i
174. names of useful files In what follows we will explain in detail how the above script works Line 1 as usual specifies the shell to be used Line 2 introduces a new shell variable called NN it is customary but not necessary to use capital letters for shell variables Unix is case sensitive so while one can use the string nn for a shell variable this would be a variable different from NN and assigns it as value the URL to be used in the netscape command mentioned in line 7 In this value file HOME htm1_files 1 HOME and 1 are themselves shell variables The value of the former is the home directory of the user home jsmith in our present example and the value of the second one is the first argument of the shell script we are in the process of describing That is if the above shell script is used in the command viewhtml example html then example html is the value of 1 viewhtml itself is the name of the shell script In line 3 the file junknetscape is removed if it exists since a leftover file by the name junknetscape could cause trouble The option f of the command rm 102 V MISCELLANEA forces removal so the user is not prompted if he or she indeed wants to remove the file The string gt amp is used for output redirection Normally the command would write its output to the screen but this the symbol gt amp makes this output go to the null device dev null instead of the screen the null device is a sort o
175. nce it is located in the directory public_html and no one else than you has read permission on this directory since its permission code is 711 So while all users can change to the directory public_html they cannot list its content by typing 1s Viewing PostScript files Many documents written in the page definition lan guage PostScript see p 79 are available on the Web PostScript is especially useful to display mathematical writings with complicated formulas Mathematical documents are often written in the typesetting language TEX see p 78 can be rou tinely converted into PostScript to convert them into HTML is often difficult if not impossible A free PostScript viewer called ghostview is available for Unix systems it is a standard part for many Linux distributions A way to view PostScript documents on the Internet is first to download them to the local system and then view them with ghostview on the local system If a link is given on a Web page to a PostScript document Netscape can be configured to automatically invoke ghostview to view it just by clicking on the link so that one does not have to go through the separate steps of downloading the document and then invoking ghostview To see whether Netscape is already so configured in say Netscape 4 51 click first on Edit on the top bar of the Netscape Window then click on Preferences in the small drop down window A large window will open up click on Navigator in the left co
176. nd b are divisible by p is allowed We will give a formal proof PROOF We will suppose that a and b are both positive the case when a or b equals 0 can easily be dealt with and when a or b is negative it is harmless to consider their absolute values instead Assume that a is not divisible by p we will then have to show that b is divisible by p With this assumption we have a p 1 Indeed p being a prime number its only divisors are 1 and p As we assumed that p is not a divisor of a the greatest common divisor of a and p can only be one As we saw above this greatest common divisor can be represented as a linear combination That is we have integers x and y such that 1 az py Multiplying both sides by b we obtain b aba pby Both terms on the right hand side are divisible by p indeed our assumption was that ab is divisible by p Hence the left hand side that is b is also divisible by p This is what we wanted to show Note that it is easy to conclude from the above lemma a similar statement for the product of more than two integers For example if for some integers a b and c and for some prime number p the product abc is divisible by p then either a or b or c is divisible by p To see this write abc ab c Then by using the lemma we can see that either ab or c is divisible by p If now ab is divisible by p then using the lemma again we can see that either a or b is divisible by p Similarly for the pro
177. ntegers n in the range 231 lt n lt 23 1 2 147 483 647 The reason that a power of two is chosen here is that the computer usually does all its calculations in binary base 2 arithmetic but in order to communicate with people on their terms it converts the results of all calculations to the decimal base 10 system unless otherwise instructed The observation that computers should use binary arithmetic is not a trivial one In the 1940s the first electronic computer called ENIAC Electronic Numerical Integrator And Calculator containing 18000 vacuum tubes used decimal arithmetic Binary arithmetic was used in subsequent computers as a result of a proposal by the mathematician John von Neumann who noted that conversion for binary and decimal arithmetic is an easy task for the computer to perform He also worked out the architecture of the modern stored program computer the architecture adopted by later computers this architecture is now called von Neumann architecture The role of this declaration is to reserve a location in the computers memory for the variable num The declaration must be followed by a semicolon As mentioned before line 1 constitutes the header of the program the rest constitutes its body The part of the program on lines 4 5 is the action part of the program enclosed between the key words begin and end The parts of the program that cause the com puter to take action are called statements Lines 4 and
178. od g r edg takes away read permission from users in the same group while the command chmod u w g x edg will take away write permission from the user jsmith herself and takes away execute permission from users in the same group Permission codes are sometimes indicated by octal i e base 8 numbers Take for example the last item from the above list and under each permission code write 1 where permission is given and zero where it is not given total 8 rw r r x 1 jsmith cored 4698 May 25 18 44 sec5 tex 110100101 The binary base 2 number 110100101 can be written in base 8 as 645 if the same permission code is desired for the file euclid_new p this can be achieved by the command chmod 645 euclid_new p 6If you are owner of the file called say myfile but you have no write permission for it upon typing 1s you will get a reply such as rm myfile override protection 444 yes no the meaning of the number 444 will be discussed just below or rm remove protected file myfile If you answer this question by typing y the file will be removed and if you answer it by typing n or anything else it will not be removed 4 X WINDOWS AND NETSCAPE 19 CHAPTER II THE WEB After an introduction to the X Windows graphical user interface GUI a brief description of Netscape is given Then we discuss how to set up your own Web page and the basic features of the Hypertext Markup Language HTML are presented 4 X Wind
179. of 8 attack symlink 113 awk 107 background running jobs in the 20 background program running in see program running in background backslash character see char acter backslash Backus John 36 bash see shell Bourne again bash_profile file 97 bashrc file 121 begin see Pascal key word begin Bell Laboratories 6 Berkeley Software Distribu tion see BSD Unix Berners Lee Tim 20 bf see TEX bf bg 125 binary arithmetic 40 binary file see file binary bold face in TFX see TRX bold face in bookmarks in Netscape see Netscape bookmarks Boole George 69 boolean type in Pascal see Pascal boolean type in Bourne shell see shell Bourne Bourne again shell see shell Bourne again breaking up Unix commands see Unix commands break ing up Brooklyn College Web site of 20 BSD Unix 6 buffers in vi 16 named 16 bye see TEX bye C shell see shell C C programming language 36 calendar Gregorian 5 76 Julian 76 Capital Lock key dangers in vi 16 caret 14 84 carriage return character 13 case see Pascal case state ment in cat 9 92 cd 10 cd 124 centering lines in TEX see T X centering lines in centerline see TFX centerline char type in Pascal see Pas cal char type in character backslash 78 end of line 34 42 character in Pascal see Pas cal char type in chmod 18 CLI see interface command line Command Line Interface see interface com
180. of the file etc The chmod on the third line is necessary since one cannot be sure that the permission codes of the compressed file will be 611 One can enable Netscape to view compressed files in a way similar to how we enabled to view PostScript After clicking on Navigator and Applications in the Preferences window as before check if compression is enabled If not then click on 7 EMPOWERING NETSCAPE 33 the button New as above and make the following entries Description gzip compressed data MIMEType application gzip Suffixes gz Application bin gunzip s Now if at the Web site http sci brooklyn cuny edu mate there is also a compressed file index html gz in the directory public_html then you can load it into a gunzip enabled Netscape by going to the site http sci brooklyn cuny edu mate index html gz However this is of limited usefulness since only the text of the index html file is compressed this way and text does not take that much time to load anyway un less very long What really takes time is the loading of the images linked in the file index html There is no use to compress these images with gzip since their for mat most often GIF or JPEG the latter stands for Joint Photographic Expert Group the original name of the committee that wrote this compression standard is already compressed and there is no sense in compressing a compressed file since in general no further reduction in the file size can
181. oices another window will open After positioning the mouse pointer in this window one can type the Web address of the College http www brooklyn cuny edu Then clicking with the left mouse button on the button labeled Open in this window will bring up the Web site Usually the Netscape window will not be able to display the whole content of the site and one can move around by manipulating the scroll bar at the right hand side of the window possibly there is also a scroll bar at the bottom One can do this either by clicking with the left mouse button on various points in the scroll bar or keeping the left mouse button depressed on the scroll button and moving the mouse pointer when the display is in the desired position the mouse button should be released In the displayed page certain locations will be active areas These are usually underlined words in color or certain parts of some pictures One can find these active areas by moving the mouse pointer onto them without depressing any buttons The mouse pointer will change shape over active areas from an arrow it will change into a hand with an index finger pointing By clicking with the left mouse button over an active area the link contained at that area will be activated and a new Web page will be displayed or possibly another part of the same Web page will be displayed The link is said to point to this new location There are many interesting things you can find on the
182. ommon divisor First note that we usually consider only positive divisors Thus the common divisors of 12 and 18 are 1 2 3 6 i e the same as those of 12 and 18 So their greatest common divisor is also 6 i e 12 18 6 Similarly 12 18 6 Every positive integer is a divisor of 0 Thus the common divisors of 0 and 18 are just the divisors of 18 The greatest common divisor of 0 and 18 is thus the greatest divisor of 18 i e 18 itself 0 18 18 Similarly 12 0 12 Note that 0 0 is undefined since any positive integer is a divisor of 0 and 0 On the other hand while it may be uninteresting to consider the greatest common divisor 12 12 the definition is meaningful in this case and we have 12 12 12 A way of determining the greatest common divisor of two integers was described by Euclid about 2400 years ago This method called the Euclidean algorithm even though it was probably not invented by Euclid himself or its minor modifications is still the best method to determine the greatest common divisor of two numbers While the greatest common divisor of 12 and 18 can be easily guessed the situation is different when larger numbers are involved We illustrate the Euclidean algorithm by determining the greatest common divisor of 546 and 422 Step 1 Divide 422 into 546 the remainder is 124 We replace 546 by this re mainder That is in place of the original numbers 546 and 422 we will work with 422
183. on changing shell variables Finally a brief section on job control is given 21 Mathematical Typesetting The best way to write about mathematics on computers is to use the typesetting language TFX pronounced tek designed and implemented by Donald Knuth TEX is now widely accepted in the mathematical community It is extensively used in producing mathematics books and journals It is also used in other sciences such as physics chemistry and astronomy where professional typesetting of mathemat ical formulas is important It is excellent for typesetting even texts not containing mathematical formulas These notes were typeset using TeX The letters TX are in fact the Greek upper case letters tau epsilon and chi except that the epsilon is shifted to produce the unique appearance The letters rex which is the lower case version of TEX form the beginning of the word technology in Greek Before you start experimenting with TFX it is best to make a new directory called something like texfiles and do all the work in this directory rather than mix works on T X Pascal and HTML in the same directory At this point it is best to use an X Windows environment such as OpenWindows on Sun Workstations because this will be needed for previewing the typeset version of work being created To start out using the text editor vi create a file called say first ter the ending tex of the file name is often required the first part of the name is
184. on line 8 will fail and so line 10 will not be executed thus the last value of 7 that is added to sum is 6 Thus in the end we have sum 04 1 4 24 3 4 54 6 1424 3 4 4 4 5 6 In general depending on the value of n we have sum 1424 34 n Soi i 1 In words the final value of sum is the sum of positive integers 1 through n This explains the text printed out in lines 13 14 of the program Problems 1 Trace through the execution of the following program That is indicate how the variables 7 sum and n change through the execution of the program and what is printed by the program 1 program example output var i sum n integer 2 3 begin 4 n 7 5 i 3 6 sum 0 7 while i lt n do 8 begin 9 sum sum i 10 i i 2 11 end 12 writeln The total equals sum 1 13 end 48 IHI PASCAL 2 Trace through the execution of the following program 1 program example output 2 var i sum n integer 3 begin 4 n 7 5 i ogs 6 sum 3 T while i lt n do 8 begin 9 i i t 2 10 sum sum i 11 end 12 writeln The total equals sum 1 13 end Compare the trace of this program to the trace of the program given in Problem 1 3 Write a Pascal program that adds up the all the even integers 2 4 6 up to a positive integer n entered at the keyboard and then prints out the result if the number n entered is even n itself should also be added and if it i
185. onditional statement is found in lines 70 77 called the case statement case daycount of 0 dayofweek Sunday es 1 dayofweek Monday ny 2 dayofweek Tuesday 3 dayofweek Wednesday 4 dayofweek Thursday 5 dayofweek Friday H 6 dayofweek Saturday end In this statement daycount is a variable called the selector of type integer and depending on its value the statement in the corresponding line is executed For example if daycount 3 the line dayofweek Wednesday is executed The selector in a case statement could be an expression of the type integer and not just a variable Next we give the listing of the whole program The comments in the program give a fairly detailed explanation of how this program works but after the listing we will add more in the way of explanations 1 program daydate input output 2 This program is calculates the day of the week 3 for each date in the Gregorian calendar that 4 is after but not including the year 1582 in 5 Western Europe and after 1752 in Great Britain 6 and its American colonies 7 var 8 day month year daystocurrent 9 leapyearcount yearcount daycount i integer 10 dayofweek packed array 1 9 of char 1 leapyear boolean 12 lengthofmonth array 1 12 of integer 13 begin 14 write Enter the date by typing the number 15 writeln of months 16 write days and years E g for Septemb
186. ot need to be run in the background If one wants to go to the same Web site in an already running Netscape but wants to use an already open window rather than to open a new one one can type netscape remote openURL http www linuxworld com More about controlling an already running Netscape in Unix can be found at the Web site http home netscape com newsref std x remote html 12The primary prompt is the value of the shell variable see p 92 PS1 and the secondary prompt is the value of the shell variable PS2 The default values for these variables are usually and gt 7 EMPOWERING NETSCAPE 35 Mozilla A new offshoot of the browser wars in which Microsoft made Internet Explorer its standard browser and thereby much reduced the use of Netscape is the browser Mozilla see http www mozilla org In the late 1990s the code for Netscape was completely rewritten and the result of this effort is the open source browser Mozilla and the new version of Netscape with version number 6 or higher An important virtue of these browsers is their strict compliance with the standards of the World Wide Web Consortium so as the prevent the fracturing of the Web The command line controls of Unix Netscape described above also work with Mozilla if one replaces the word netscape with mozilla provided Mozilla is installed on the system 36 III PASCAL CHAPTER III PASCAL We give an introduction to the Pascal programming langu
187. otation used in Pascal For example 26 mod 3 2 We have Qnew bmoda and bnew b moda In Pascal one would be tempted to write the following program segment to imple ment this 14 IMPLEMENTING THE EUCLIDEAN ALGORITHM IN PASCAL 55 a b mod a b a This however will not work If one starts with the values a 124 and b 422 then the effect of the first line will be a 422 mod 124 that is a 50 Then the result of the second line will be b 50 i e b is assigned the new value of a whereas it needs to be assigned the old value of a Therefore before a is changed its value needs to be preserved for this we introduce a new variable called temp The correct program segment will therefore be temp a a b mod a b temp In the Euclidean algorithm this step has to be repeated until a zero remainder is obtained The Pascal program accomplishing this can be easily written At the beginning lines were added to read in the data and at the end a line was added to print out the result The whole program is as follows 1 program euclid input output 2 var a b temp integer 3 begin 4 write Type a a must be a positive integer 5 readlin a 6 write Type b b must be a positive integer 7 readlin b 8 while a lt gt 0 do 9 begin 10 temp a 11 a b mod a 12 b temp 13 end 14 write The greatest common divisor of the above 15 writeln numbers equals
188. otocol address of your local machine It is something like 148 243 14 91 but of course not this number we will soon indicate some ways as to how to find out this number If you connected to an Internet service provider your IP address will probably change each time you are connected to the Internet this is called dynamic IP address allocation an IP address that always remains the same is called static IP address Finding out your IP address The way you find out your IP address may depend on what operating system you are using at home For example assume 27 REMOTE ACCESS 127 you are using a machine running Red Hat Linux 6 0 and have an account with the Internet service provider Mindspring we mentioned the version of Linux for the sake of being specific since the files we will mention may be located at slightly different places in different versions of Unix As a first step connect to your Internet service provider Mindspring using the protocol ppp ppp works through phone lines and modems and will make your computer a part of a larger network Note that not all Internet service providers allow ppp connections for example America Online does not so when using Linux you are restricted to certain Internet service providers that support it You can find Mindspring at http www mindspring net At the time the ppp connection is made your computer writes your local IP address into the file var log messages Since the file
189. ows and Netscape After logging in at a Sun workstation you may choose to work directly at the standard Sun console this is what you get after logging in You get more flexibility by entering the OpenWindows environment Openwindows is based on X Windows created at the Massachusetts Institute of Technology in the 1980s Most Unix sys tems use a form of X Windows and so whatever you learn on Sun workstations can be transferred to other implementations of Unix You can enter the OpenWindows environment by typing openwin Several windows will open and you can do your work in any of these windows by typing commands as if you were working at the console You can do different work in each of the windows at the same time You can open new windows as you need them and close unneeded windows First you need to learn how to manipulate windows by using the mouse This is fairly easy and a few minutes help session with a friend is much more productive than reading any manuals After learning the basics you may refine your windowing skills if you wish to do so by reading parts of the manual given elsewhere in these notes The most important point is that the active window is always the one to which the mouse is pointing before you can type in a window you need to move the mouse so that it points to the window in question After finishing your session you must first exit OpenWindows usually by using the mouse and then you must log out at the console
190. pe was not running Line 29 introduces the alternative when Netscape is already running and in line 30 the editor ed is opened to deal with this situation First lines 32 and 33 are added as first and second lines respectively to the currently empty file junknetscape line 35 inserts the content of the argument file 1 after line 1 i e beginning line 2 of the file being edited so the line that is currently the second line will move further down Line 36 joins the first through the last but one line of the file being edited the last line the one that was entered as the second line in line 33 will not be joined Line 37 and 36 writes out to the file and quites the editor and the word fi on line 37 marks the end of the the conditional shell command that is the later part of the script deals with the situation independently whether or not Netscape is already running The here document in lines 41 45 changes all occurrences of a comma to the string 2C in line 2 of the file junknetscape This line contains the Web address in a Web address a character can always be replaced by the the hexadecimal ascii code of the character preceded by the percent sign 4 2C happens to be the hexadecimal ascii code of the comma Note that the file junknetscape will contain a Unix command a comma in a Unix command would be misinterpreted since commas do occur in some Web addresses the command would fail without the above substitution Most Web
191. permission codes for 23 Web pages secret 29 Web site 20 Web site of the World Wide Web Consortium see World Wide Web Consortium Web site of 143 Weinberger Peter J 107 whereis Unix command 31 which Unix command 31 while do see Pascal while do statement in whoami 11 width in writeln statements see Pascal writeln width of fields Wiles Andrew J 83 window locked up 125 Windows 7 95 7 98 7 2000 7 NT 7 compared to Unix see Unix compared to Windows NT Wirth Niklaus 36 World Wide Web 5 19 World Wide Web Consor tium 28 Web site of 29 write see Pascal key word write writeln see Pascal key word writeln see Pascal key word writeln writing to a file in Pascal see Pascal writing to a file X windows 19 xdvi T X previewer see TEX xdvi previewer xhost 126 xterm 124 YMMV 29
192. provided the network has a properly configured World Wide Web server Afterwards in Chapter III the programming language Pascal is discussed the implementation in Pascal of the Euclidean algorithm and its extensions are discussed then applications to print truth tables and to find the day of the week of any date in the Gregorian calendar are given Chapter IV outline a mixture topics such as the mathematical typesetting language TpX electronic mail some simple shell scripts useful for writing electronic mail and source scripts useful in avoiding the need of typing long directory names These notes were originally written between May 22 and July 13 1997 The text was revised a number of times between December 1997 and January 2003 many misprints were corrected and hopefully only a few new ones were introduced We are grateful to Nancy McGough and to James Rowe for suggesting numerous changes and corrections Nancy McGough s Web site is http www ii com While effort was made that the notes be as thorough and accurate as possible further revisions are likely to incorporate many changes It will be appreciated if suggestions for such changes are brought to the author s attention 6 I UNIX CHAPTER I UNIX After a brief description of the basic Unix commands the vi text editor discussed text editors are needed to create any piece of writing on the computers Then permission codes are described Familiarity with permission codes is
193. pt but after the shell script finishes the status quo ante will be restored That is the shell script cd usr bin ls will change to the directory usr bin and then list its content but after it finishes you will be in the directory where you started the shell script and not in the directory usr bin So what are you supposed to do if you often have to examine the content of a directory such as usr lib texmf texmf tex amstex base Perhaps you want to do this since certain things do not work properly on your system and you want to understand why One thing you can do is to define an alias User defined aliases are usually placed in the kshrc file this stands for Korn shell root commands in the user s home directory C shell uses cshre and Bourne again shell uses bashrc The line you would place in this file may look like alias cdtexbase cd usr lib texmf texmf tex amstex base This will allow you to type cdtexbase instead of having to type 122 V MISCELLANEA cd usr lib texmf texmf tex amstex base These aliases are not effective immediately they will take effect after first logging out and then logging in again There are many instances that such aliases are useful For example we discussed the command xdvi s 4 thorough first amp to display preview the typeset tex file first dvi above By adding the alias alias texview xdvi s 4 thorough to the file kshrc we will be able to type the shorter comm
194. r of leap years is added so each leap year is counted twice the current year is not counted yearcount year 1 leapyearcount yearcount div 4 yearcount div 400 yearcount div 100 yearcount yearcount leapyearcount now we can calculate the daycount which is essentially the date of the week daycount yearcount daystocurrent mod 7 now daycount is related to the actual date of the week the following table can be set up by printing out daycount for a date where the date of the week is known case daycount of 0 dayofweek Sunday oF 1 dayofweek Monday or 2 dayofweek Tuesday 76 IV APPLICATIONS OF PASCAL 72 3 dayofweek Wednesday 73 4 dayofweek Thursday 74 5 dayofweek Friday ag 75 6 dayofweek Saturday 76 end 77 writeln dayofweek 78 end The Gregorian calendar named after Pope Gregory XIII 1502 1585 pope 1572 1585 is the calendar currently in use According to it a year consists of 365 days except for leap years consisting of 366 days A leap year is a year whose number is divisible by 4 except for years whose number is divisible by 100 among these years only those are leap years whose number is divisible by 400 This is an improvement over the the Julian calendar introduced by Julius Caesar in 46 B C according to which every fourth year was a leap year The above program works only for the Gregorian calendar In line 8 the variables day month y
195. r page see lpr header page suppressing 135 here document see script shell here document Hewlett Packard 6 hidden file see file hidden HOME see shell variable HOME host name 126 HP UX 6 HTML 5 19 23 29 4 0 specifications on the Web 29 accented letters in 26 anchor in 26 attribute 26 attribute values lt LEFT gt of lt ALIGN gt 26 lt LEFT gt of lt CLEAR gt 28 attributes lt ALIGN gt 26 lt ALT gt 26 lt BORDER gt 26 lt CLEAR gt 28 lt HSPACE gt 26 lt SRC gt 26 centering phrases in 26 comment in 26 diacritical marks in see HTML accented letters in element 26 heading in 26 horizontal rule in 26 hyperlink in 27 including images in 26 legal issues 29 line break in 26 paragraph in 28 tag 25 paired in 25 solitary in 26 tags lt BODY gt 25 lt BR gt 26 lt CENTER gt 26 lt H1 gt lt H6 gt 26 lt HEAD gt 25 136 INDEX lt HR gt 26 lt HTML gt 25 lt IMG gt 26 lt TITLE gt 25 target too long in 28 title in 25 Uniform Resource Identi fier in 28 Uniform Resource Loca tor in 28 URI in see HTML Uni form Resource Identifier in URL in see HTML Uni form Resource Locator in hung window see window locked up Hypertext Markup Language see HTML IBM 6 identifier seePascal identifier 38 if command in in Bourne shell see shell Bourne if command in statement in Pascal see Pascal statement in if inclusive or 68
196. re ordinary files The next nine letters afterwards are the permission codes the first three after the very first letter concerns the user or rather the owner of these files jsmith in this case the next three concerns users in the same group or groups and the last three concerns all other users The letter r means the file is readable w means the file is writable i e can be changed or written into and z means the file is executable what this last one means will be explained later For example the user jsmith the owner of these files can read write into or execute the file edg Users in the same group can read and execute this file but cannot write it All other users can read this file For directories the meanings of permission codes are not quite intuitive so we give some explanation If you have read permission for a directory you can list its content by using the 1s command If you have write permission for it then you can create new files in the directory and delete any files with the rm command for which you have write permission if you do not have write permission for a file you cannot usually delete it even if you have write permission for the directory containing it Finally if you have execute permission for it you can use the cd command to change to it Permission codes can be changed by the chmod change mode command The command chmod o x edg adds execute permission to other users the one chm
197. reate the file HOME marks sentmark with a slightly different content Letter sent ony Aside from the missing colon first a space character needs to be added after the text we indicated this space as u we did not indicate the other space characters in the line whose presence is clearly seen by the gap left between words Second there must not be an end of line character at the end of the line If this can be accomplished then line 4 in the the above shell script will not put the date on a separate line Since the editor vi automatically writes the end of line character at the end of the line vi does not seem to be suitable for creating this file On the other hand the file can easily be creating by compiling and running the following Pascal program 1 program writesentmark sentmark 2 var sentmark text 3 begin 4 rewrite sentmark 5 write sentmark Letter sent out on 6 end This program does not use the files input and output so these are not indicated On the other hand it will write to a file called sentmark so this is indicated in line 1 In line 2 sentmark is declared a text file In line 4 the meaning of the rewrite statement is to destroy the previous content of the file sentmark and to open it for writing In line 5 the write statement is used to write into this file When the Pascal statement write writes to a file rather than to the screen this file has to be identified as the first argument of the write
198. reated later For this purpose there is a file called null tex somewhere in T X s own area this file contains nothing at all its only purpose is to use its name in such emergency situations Typing null will allow T X to terminate As a simple experiment to see how T X works using the text editor vi create a file called fermat ter with the following content at this point it is best to use an X Windows environment such as OpenWindows on the Suns because this will be needed for previewing the typeset version of the file 1 input amstex 2 documentstyle amsppt 3 magnification magstep1 4 5 head 6 Fermat s Last Theorem 7 endhead 8 9 Around 1637 10 the French lawyer and amateur mathematician 11 Pierre de Fermat 1601 1665 wrote on the 12 margin of his copy of a book by Diophantus 13 the Greek mathematician of the third century 14 smc a d a sentence that can be rendered 15 with modern mathematical notation as follows 16 17 There are no positive integers n gt 2 a 18 b and c such that 82 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 V MISCELLANEA a7n b n c n holds I have found a marvelous demonstration of this but there is not enough space on the margin to write it This statement is now called it Fermat s Last Theorem Observe that for n 2 the above equat
199. ressing the Enter key on the keyboard normally signifies the end of a command but if the end of line character is quoted the computer displays the greater than sign gt at the beginning of the next line that is the sign gt is not typed by the user and the command than can be continued on the second line The character amp at the end of the second line makes sure that the process runs in the background so that the window in which we typed the above command will remain usable this was explained in p 20 after we first discussed running Netscape see Section 26 for more information about running jobs in the background The above command could have been typed on a single line but since it is quite long it is convenient to break it up The character gt at the beginning of the second line in the command above is the secondary shell prompt while the dollar sign at the beginning of the first line is the primary or main shell prompt Both prompts can be changed by the user so the symbol at the beginning of the second line may be different One can also give commands from the command line to Netscape when the latter is already running For example the command netscape remote gt openURL http www linuxworld com new window opens a new window at the site http www linuxworld com in an already running Netscape Note that as above we used two lines to write this command Also observe that this command does n
200. revious directory by typing cd This would not work here because the way the sc alias was set up the previous working directory would be HOME 1ib sources There are other uses of the sc alias than changing directories The following two files in the HOME 1ib sources directory might be useful for changing the shell variable PATH The file changepath would have the content oldPATH PATH PATH HOME bin PATH export PATH oldPATH and the file restorepath would contain PATH 01dPATH export PATH This may be a solution preferred to putting these changes in the profile file in case these changes are required only rarely 26 Job Control We already talked about running programs in the background The typical ex ample was to run Netscape in the background by typing netscape amp The ampersand amp at the end of the line indicates that the program is to be run in the background the reason for running the program in the background is to free up the window for other command to be typed if a command is run the usual way i e in the foreground then one cannot type another command in the same window until the command finishes yet Netscape will not finish until one closes the Netscape window by exiting Netscape Another instance of running a program in the background is to open a new window by typing xterm amp If you forget to run this program in the background i e if you type xterm 26 JOB CONTROL 125 the new
201. rking directory referred to as However there are security considerations that make in inadvisable to put your working directory in the seach path as discussed at the Web site http www chicagotribune com tech developer article 0 2669 2 4 4389 FF html this is a single line scrolled over Basically the reason is that an intruder can put executable programs in your some of your directory and you can run these inadvertently Imagine that an intruder puts a script called 1s into a directory of yours that will erase all your files in that directory when run So when you type 1s in that directory instead of listing the content of the directory all the files got erased This would only happen though if precedes the directory bin the directory that usually contains the program 1s in the execution path For this reason even if you include the execution path it must be the last item there Clearing Netscape s cache At the end of Section 4 we discussed that the simple command 19It makes the change available to subshells 23 SHELL SCRIPTS 99 rm rf when executed in the directory netscape cache can be used to clear Netscape s cache on the other hand executed in the wrong directory this command can cause disaster It is much safer to use a single line shell script called say netscape clear containing the single line rm rf HOME netscape cache to perform this task Compiling Pascal programs A simple
202. rogrammed to require you to change your pass word when you log in the first time For this reason it is best to change your password immediately after you receive your account so that your work will not be interrupted at a later time You can change your password by typing passwd The symbol at the beginning of the line is the prompt written by the computer so only the word passwd is typed by the user The computer will respond with something like Password After typing in your new password the computer will ask you to repeat the new pass word After entering the same new password twice the password will be changed The above dialog can be different depending on the system used For example it can go something like this passwd Type current password Type new password Retype new password Password has been changed Here it is assumed that after the colon each time you typed the corresponding password note that these passwords will not appear on the screen for reasons of security Files and directories The information on computers is stored in files These are connected segments of data we will refrain from an abstract definition There are several kinds of files the two main types are text files and binary files Ba sically text files are files that you can read if you have permission binary files will not make sense if you try to read them Often text files are called not quite correctly ASCII files AS
203. s 13 14 at the beginning of the file being edited since these are written in separate lines two separate lines will be added The letter w instructs ed to write the result of the editing out to the file being edited this works in much the same way as the command w works in vi in command line mode Finally q in line 18 quits ed and the end of the here document is marked in line 18 Line 19 is now a command to be interpreted by the shell it will open up the file in vi for further editing We already commented between the similarities of ed and vi To mention further similarities versions of the command a in lines 4 9 and 12 in vi are somewhat analogous to pressing a in vi command mode which causes a change to insert mode see p 13 and the period in lines 6 11 and 15 is similar to pressing the escape key in vi insert mode which causes a change to command mode see p 13 Locations for executable files When executing a program one can state the name of the program with the full directory path to the program s name For 23 SHELL SCRIPTS 97 example to start vi you can type bin vi Actually on some systems vi is located at a different place so you may have to type usr ucb vi However as you saw above you can start up vi simply by typing vi The reason is that the system searches at certain locations for executable files and it will execute the file at the first location it finds it The locations it searches are
204. s a source of authoritative information At this site at the address http www w3 org TR REC htm140 one can find the specifications of HTML 4 0 Legal issues Please note that putting a page on the Web constitutes publica tion and as such there are certain legal issues that need to be kept in mind First a publication may be libelous or may violate copyright laws or obscenity laws Fi nally the College may withdraw computer privileges upon the publication of certain material that violates College s acceptable use policies It is easy to use common sense to safely stay away from the pitfalls in order to navigate the fringes you need to study the issues involved carefully Geekspeak When trying to read Web pages about computers you will often run into technical jargon that can make your reading difficult On occasion you may also run into fashionable geek slang that will further obscure your reading material An example for the latter is YMMV which stands for your mileage may vary For instance the writer may talk about the installation of a certain software explaining that you should except such and such a performance but YMMV meaning that the result you get may differ depending on your setup At the site http online today com geekspeak you can find a dictionary of technical jargon and slang that may prove helpful We would discourage the use of geek slang and excessive technical jargon since it is much b
205. s an empty file and the command chmod afterwards changes its permission code to the code desired In practice instead of using the command touch one can use a text editor such as vi to create the file index html and then use chmod to change the permission code In fact it is advisable to check the permission code at the end by typing ls l index html since some of the manipulations of this file may have changed the permission codes and if necessary to use chmod to change the permission code to 644 This permis sion code allows anyone in the world to read the file index html but does not allow them to write to this file The next task is to actually write the file index html This can be done by typing vi index html and then typing the appropriate text into the file In the next section we will discuss what this text ought to be 6 Hypertext Markup Language The file index html has to follow the format that is syntax of html or Hypertext Markup Language To explain how this is done consider the Web page displayed on p 27 The index html file specifying this Web page used to be located at the site http sci brooklyn cuny edu mate 24 Il THE WEB In July 1998 this site contained the following text note that the site has since been updated and some of the links in this file are no longer valid oono AUNE PRPPPKRBP PWWWWWWWWWWNHOHNNNNNNNNNFPRP RP RP RP RP YP PY NOomnRPRWNRrFPOOAN ODAPWNHNHRFR ODADAAN ODARPWNHRFHO
206. s in a directory and you type list the answer most likely will be ksh list not found where ksh refers to the shell running Korn shell the command to list the files is 1s and not list You may want to add other directories to be searched for executable files You can do this by adding an entry in your profile file in Korn shell located in your home directory note that the dot at the beginning of the file name indicates that this is one of those hidden files by typing 1s the name of this file will not be listed you need to type 1s a Korn shell uses profile C shell uses login and the Bourne again shell uses bash_profile Anyway if you are using the Korn shell you may make the following entry in your profile file PATH PATH HOME bin export PATH The second line may already be there in that case you do not need to add it but you have to make sure that the first line is added before the occurrence of the second line The first line modifies the value of the PATH variable it adds the directory which refers to the present working directory and the bin directory in your home 98 V MISCELLANEA directory in the search path The second line makes this change effective You only need to make these changes if the PATH variable does not contain these directories While it is convenient to have the present working directory in the execution search path it is somewhat of a security risk this is discussed below
207. s not running and is false otherwise see the discussion of line 4 of the script viewhtml in page above If Netscape is not running in line 18 Netscape s cache is cleared and in line 19 its lock file is removed in case if was left over as a result of a crash or improper termination of Netscape Lines 20 28 an here document using the editor ed is used to edit the currently empty file junknetscape Line 22 puts the word netscape in the first line line 24 reads the content of the file 1 the argument to the script beginning line 2 of the the file junknetscape It is permissible to have the Web address contained in the file 1 to be broken up into several lines therefore in line 25 lines 2 through the last line refers to the last line of the file being edited of the file junknetscape are joined so the file will now have exactly two lines Note that the sign in line 25 is quotes i e preceded by the Unix quote character the shell will remove the quote character so the editor ed will see the sign without the preceding it if it were not quoted the shell would interpret j as the value of a shell variable called j before the editor ed would get at it we have met this kind of situation in here documents before Line 26 writes out the content of the editors buffer to the file being edited and line 27 quits the editor Note that all this happened in a region of a conditional statement that was executed in case Netsca
208. s odd then it should not be added since we are adding only even integers 4 Write a Pascal program that adds up the all the odd integers 1 3 5 up to a positive integer n entered at the keyboard and then prints out the result if the number n entered is odd n itself should also be added and if it is even then it should not be added since we are adding only odd integers 12 Conditional Statements Try to run the first program of the preceding section with the value n 65536 typed in when the program asks you to type a value for n do not try this with the second version with the writeln statements for tracing inserted the printout will be unmanageable the tracing version should only be run with small values for n perhaps not larger than 20 The printout at least with the version of Pascal installed at the Atrium will be as follows The sum of integers from 1 through 65536 equals 2147450880 This result certainly cannot be correct since the sum of positive numbers must be positive In fact the correct value of the sum is 65 536 X i 2 147 516 416 i l 12 CONDITIONAL STATEMENTS 49 Now the reason for the the incorrect answer is clear As we saw earlier the largest integer that can be represented by the Pascal compiler at the Atrium is 931 1 2 147 483 647 and the value of the above sum is somewhat larger than this integer On the other hand 65 535 Ss i 2 147 450 880 i l is somewhat sma
209. s true is that in fact all the numbers occurring in the course of the Euclidean algorithm are so expressible Indeed we using the above example of the numbers 422 and 546 we have 546 422 0 546 422 422 1 546 0 124 422 1 546 50 422 4 546 3 24 422 9 546 7 2 422 22 546 17 The first two equations here are obvious Each of the other equations can be derived from the preceding two equations To derive the fifth equation for example recall that 24 is the remainder when 50 is divided into 124 This is expressed by the equation 124 2 504 24 saying that 2 is the quotient and 24 is the remainder of the division 124 50 24 can be expressed from here as 24 124 50 2 where we found in convenient to change the order of the factors in the product Taking the expression for 124 from the third and the expression for 50 from the fourth equation we can now write this as follows 24 422 1 546 1 422 4 546 3 2 This can be algebraically simplified as 24 422 1 4 2 546 1 3 2 If we carry out the operations indicated in the parentheses we obtain 24 422 9 546 7 Thus we obtained the fifth equation from the third and fourth equations as we promised we would do The Euclidean algorithm performed with these additional calculations so that the greatest common divisor is obtained as a linear combination of the origina
210. safe since not much can be lost by removing an empty directory In Unix parlance r after the command name rm is called an option You can change the name of the file sec2 to section2 by the command mv sec2 section2 This is the first command that we mentioned that has two arguments sec2 and section2 There is a danger here if there already exists a file called section2 this command will destroy it and replace it with the file sec2 The mv command which stands for move but typing move would not work behaves differently if the second argument is an existing directory For example if there is a directory called pascal_examples in the current directory then mv sec2 pascal_examples moves the file sec2 into the directory pascal_examples The command 12 I UNIX cp sec2 sec2 backup will copy the file sec2 to sec2 backup if the file sec2 backup already exists its old version will be lost Assuming that pascal_examples is an existing directory in the current working directory typing cp sec2 pascal_examples will copy the file sec2 into this directory if the file pascal_examples sec2 already exists its old copy will lost Finally cp r pascal_examples pascal_examples bak will duplicate copy the directory pascal_examples along with all its subdirectories onto a new directory pascal_examples bak if a directory by this name already exists it will not be destroyed a copy of pascal_examples with all its subdirectories
211. scal programs 10 More on Pascal The following program is now easy to understand 1 program example3 output var numi num2 sum integer 2 3 begin 4 numi 15 5 num2 12 6 sum numi num2 42 IHI PASCAL 7 write The sum of numi 1 and 8 writeln num2 1 is sum 1 9 end On line 2 three variables called num1 num2 and sum are declared to be of type integer The spaces in this line except for the first one are added only for easier readability they can be omitted and the line can also be written as var numi num2 sum integer we omitted the line number which is not part of the file containing the program The first space is of course required in order to separate the key word var from the identifier num In line 6 the assignment statement includes a simple arithmetic expression Arith metic expressions can be written in much the same way as they are in mathematics The arithmetic operators allowed are for addition for subtraction and sign in version i e for changing the sign of a number as in the expression 5 changing the number 5 to 5 for multiplication that is 5 times 4 is written as 5 4 rather than the usual mathematical notation 5 4 the reason for this is the limitations imposed by the keyboard for division however even if performed on numbers of the type integer the result will be a number of the type real the type real has not yet been disc
212. scribed by the string f print 1 P the syntax must be exactly as given above with the right quote signs included The action is to take the first field of each line and write it to the standard output In the above command the standard output is redirected to the file junkkill1 Thus the content of the file junkkil11l0 being 10522 pts 16 00 00 01 netscape commun 10532 pts 16 00 00 00 netscape commun when the awk command is issued as seen in the output of the script viewhtml described above as a result of this command the file junkki11 will contain the first field of each of these lines 10522 10532 that is the process id s associated by the above processes Lines 6 13 of the above script is a here document see p 95 In line 6 the string 2 gt dev null is used to redirect the standard error output of this command to dev null which is nothing at all the purpose of this is to keep this output from cluttering the screen Above we used the symbol gt amp to redirect the standard error output see p 102 here we used the symbol 2 gt Both works equally well The explanation for the latter symbol is that the standard error output is called output stream 2 the standard output is called output stream 1 and 1 gt instead of gt can be used to redirect the standard output In the here document in lines 6 13 the editor ed see 95 is used to edit the file junkkil1 Line 6 of the script opens the editor at
213. see p 98 You may place some shell scripts that you wrote into the bin directory in your home directory for example this is where the scripts email and letter discussed above belong Occasionally different programs with the same name may be found at different locations This may cause confusion It may happen that you are used to running some program called useful_program and one day the behavior of this program changes possibly you are running a different program by the same name You may check which program program you are running by typing which useful_program cf p 31 for the which command The answer may be something like usr local bin useful_program The present working directory in the search path Sometimes the present working directory is included in the PATH In this case the command echo PATH may produce the reply bin sbin usr bin usr sbin usr local bin usr local sbi n usr bin X11 usr X11R6 bin root bin usr local sbin Here the dot at the end indicates the present working directory In this case if you have a program called say my_program in your in your present working directory you can run it simply by typing my_program Even if is not listed in the PATH variable you can run this program in your present working directory by typing my_program This works since rather than just giving the name of a program it gives a path to it as the file with the name my_program in the present wo
214. space character to be clear In the first string the shell quote character is stripped away by the shell as above so the first string is actually which just as in vi refers to the end of the line That is the second string gets added at the end of each line of the file junkkil1 except for the last line In the second string 4 there are three backslash characters The first one of this is stripped away by the shell as a quote character the second one is stripped away by the editor ed again as a quote character Only one backslash remains in the end That is what is added at the end of each line of the file junkkil1 except for the last one is the string That is after this action the file junkkil1 looks as as lines 5 7 of the script killns being discussed kill s 9 10522 10532 In fact the file junkkil1 does not yet look like this so far all the editing took place temporary file created by the editor ed and only the command w in line 11 writes this into the file junkkil1 similarly to the way the command w works in vi see p 15 The command q in line 12 quits the editor and the percent sign in line 13 terminates the here document Line 15 of the script executes the command in the file junkkil1 i e sources cf p 122 The command executed is the same as kill s 9 10522 10532 would be on the command line since the quoting of the end of line character in the file junkkil1 kill s 9
215. statement As we mentioned earlier the write statement does not add an end of line character at the end so the file written by this program will be exactly as desired If the shell script email is now run with the modified version of the sentmark file instead of lines 14 15 above we obtain a single line Letter sent out on 15 Sat Jun 21 21 19 23 EDT 1997 The next question to be solved is how to create the file cmuser5 i e the letter that was sent out Some parts of this file have to be typed at the time the letter is written but there are parts of it that are common to all letters sent out so there should be a way to create this common part of the letter once and for all In fact this is accomplished by the following shell script we call letter 1 bin sh 2 cat HOME marks regards gt gt 1 94 OAWAND OTF W 10 Tt 12 13 14 15 16 17 18 19 Here in line 5 we indicated the space characters at the end of the line there are 11 spaces at the end of the line at other places the space characters were not indicated since their presence is clear from the gaps left in the text After making this file executable with the chmod command one can create the skeleton of the file V MISCELLANEA ed 1 lt lt 0a Dear 2 uuu uuu ir date 1 2j a 0a vi 1 cmuserd by typing letter cmuser5 Charley If the file cmuser does not exist then the the vi editor will open up with the following content 1
216. stems SunOS and Solaris Actually on Suns the alias alias null cat gt dev null behaves better than the one given above Another possible version is alias null cat gt dev null The way this and the alias given above misbehaves is by adding an addressee listed in the mail header such as sending machine domain name cat gt dev null while the version without parentheses does not add this addressee on the Suns the version without parentheses complains about Unbalanced gt in Linux 22 ELECTRONIC MAIL 89 1 t cmuser math some school edu 2 s Your suggestion 3 Dear Charley Sat Jun 21 21 06 51 EDT 1997 4 I think I can make your suggestion work I have 5 to think about it a little more however 6 7 Regards 8 9 J F Smith 10 jsmith math myschool edu 11 http www math myschool edu jsmith 12 7 13 Letter sent to Charles K User The numbers on the left are as usual line numbers and are not part of the file Lines 1 2 12 contain so called tilde escapes i e lines whose first character is a tilde tildes occurring at positions other than the first characters of some line have no special effect In line 1 t adds the address on that line to the recipients of the letter There can be more than one address on a line addresses should be separated by a space There can be several lines with the t escape In line 2 s states the subject of the letter the subject can be left empty but
217. sting of a single character or whole words could be used 8 an important point however is that the mark used cannot occur inside the here document because as soon as that mark occurs the here document ends The symbol lt lt obtained by typing two lt signs indicates that what follows is a here document and the symbol following it will be the delimiter of the here document In line 4 the ed command Oa indicates that the text following in the next few line s are to be added at line 0 i e at the beginning of the file being edited the period by itself in line 6 marks the end of the text to be added i e at 18 A here document where a whole work used as a mark is given in p 101 96 V MISCELLANEA present the text to be added is only the text in line 5 Here 2 is to be interpreted as the second argument of the shell command letter cmuser5 Charley i e Charley including the comma You may want to address this person as Charley or as Professor Cmuser accordingly you may want to type the com mand lines letter cmuser5 Charley letter cmuser5 Professor Cmuser In the last example the quote character will be stripped by the shell program i e you will properly obtain the line Professor Cmuser rather than gt Professor Cmuser Instead of single quotes double quotes shift can also be used i e the command line could have been typed as letter cmuser5 Professor Cmuser In line 7 the ou
218. take up less room in the memory than integers and other data types so a sequence of characters can be placed in the memory more tightly than a sequence of integers for example Packed arrays take up less room but access to individual members of the array is often more costly than if the array was not packed however we will not need access to individual members of this array we will only be interested in the whole word spelled out by the array A kind of loop statement not discussed before the for statement is used in lines 50 51 for i 1 to month 1 do daystocurrent daystocurrent lengthofmonth i In this statement the statement in the second line is repeatedly executed starting with the initial value currently 1 of the control variable i at present incrementing this value by 1 for each new execution the statement is executed the last time with final value currently month 1 of the control variable The variable is usually an integer it is allowed to be any ordinal data type but we will not discuss what these are and the initial and terminal values can be expressions these expressions are 74 IV APPLICATIONS OF PASCAL evaluated only once when the loop is entered It is not permissible to change the value of the control variable inside the loop It is easy to see that this loop adds the values of lengthofmonth i for i with 1 lt i lt month 1 to the starting value of the variable daystocurrent A new kind of c
219. tatement else statements The semantics of this statement is straightforward if condition is satisfied then statement is executed otherwise i e if if condition is not satisfied statement is executed The else part can in fact be omitted The syntax of this version if if condition then statement According to the semantics of this version if condition is satisfied then statement is executed nothing is done otherwise The if statement is a type of conditional statement another type of conditional statement is the case statement discussed later in Section 20 on p 74 The above program contains the first version of the if statement in lines 6 16 Line 6 contains the condition line 7 contains statement and lines 9 19 constitute statement 2 as can be seen in the present case statement is a compound statement Also note the close similarity between this program and the first program of the preceding section In fact lines 4 5 and lines 9 19 were copied from that program A minor modification was made in line 18 a fourth item was added in the writeln statement The effect of this is to print a period at the end of the line If this program is run with n 50000 then the condition in line 6 fails and so the statement in lines 9 19 will be executed the printout will be as follows Type n n must be a positive integer 5000 The sum of integers from 1 through 50000 equals 1250025000 here the number 5000 is in fact type
220. terminate say the third of these programs by typing kill 9 3 The command kill has a number of options 9 is the most effective but it might be preferable to use a more gentle kill we will not discuss this issue here but you can study the on line manual of kill Both stopped programs and programs running in the background can be killed this way One should only kill a program when a more gentle option is not available for example one can terminate xterm by typing exit in the xterm window one wants to close except when the window is stuck or hung in other words locked up i e is non responsive to keyboard input It is important to know about killing jobs because often the computer will not allow you to log out if there are stopped jobs It may happen that when you want to log out by typing logout the computer responds with There are stopped jobs 27The command kill s 9 3 works exactly the same way 126 V MISCELLANEA By killing these jobs one will be able to log out Usually however even without killing these jobs one can log out by typing logout again and the stopped jobs will be flushed killed 27 Remote Access Remote shell Computers at the Atrium can be accessed on the Internet In Unix the command to reach a machine on the Internet would be rsh 1 login_name machinename its brooklyn cuny edu Here login_name needs to be replaced by the login name of the user and machin name by the nam
221. the shell escape character In vi this means the following In command line mode one can enter a Unix command after typing an exclamation point For example while in command mode typing 1s lists the files in the current directory i e in the directory in which vi was invoked Including the space here is optional That is typing gt pwd 16 I UNIX will print the present working directory These examples also show that typing a space after the exclamation point is optional Buffers You can put various parts of the text into temporary storage called a buffer For example typing yw on the first character of a word puts yanks this word into the buffer To insert this word somewhere else in the text move the cursor to the intended position then typing p will write put the content of the buffer i e the word just yanked after the current cursor position while typing P puts the content of the buffer before the current cursor position In addition to the single unnamed buffer there are named buffers to each lower case letter of the alphabet To yank a word into the buffer named s type syw on the first letter of the word and to put the content of this buffer into the text type sp or sP in the appropriate cursor position To yank a whole line type Y or cY to yank it into the buffer named c to yank the text from the current cursor position to the character say s on the same line type yts read yank to s
222. to the address described by this string this address is however a nonsense address In line 2 in this script the option vI is used for Linux instead of v as explained at the end of the preceding section In line 4 the string after the word date formats the date for a 12 hour clock rather than the 24 hour clock provided without the use of this string 17This description is only a rough outline of the difference between compilation and interpreta tion of a language An interpreter reads the source program statement by statement and causes the computer to perform the required action whereas a compiler processes the whole source program and translated it into a different language that is easier for the computer to process For example the computer language Perl is a high level language that is first processed by a compiler into a simpler language and then and interpreter causes the execution of the program described in this simpler language The output of the compiler is however not kept for later use 92 V MISCELLANEA cat gt dev null which is the way the null alias was specified in the file mailrc here we cannot use this alias since aliases in maiirc are not recognized in commands in shell scripts it is easy enough to write out this alias once when writing the script email The second argument in line 2 is 1 this refers to the first argument used when running the shell script at present the shell script was r
223. tput there are six fields in this output and these six fields will be the arguments of the echo commands These six fields will be sent to the standard output separated by single spaces That is the output of the command echo cat argfile in the present example is 123456 With these considerations one can see that the command kill s 9 in lines 2 3 in the shell script killnsO above is executed with the arguments 10522 and 10532 i e with the fields in the output of the command between two left quotes in line 3 of the script That is the effect running this script is the same as executing the command kill s 9 10522 10532 instead of course the two process id numbers on the right change with each instance of running the script That is the processes associated with Netscape will be killed The effect of redirecting the standard error output in line 4 will be that harmless error messages will be suppressed If we were to delete line 4 from the script killns0 then running the script might result in the following message kill 10532 No such pid This is because the second process associated with Netscape the one with process id 10532 is dependent on the first one i e the one with process id 10522 Once the first process is killed by the kill command the second one dies a natural death so when the kill command tries to kill the second process it no longer exists so we get the above error message Since the error mess
224. tput of the date command is placed into the file being edited after line 1 In this line 1 is the line number of the file being edited r means read into this file the exclamation point indicated that what is going to be read is the output of a Unix command and date is the Unix command in question The output of date is the current date and time Line 8 says that lines 1 and 2 have to be joined into a single line In line 9 the letter a indicates that the text in the next few lines will have to be added again only one line line 10 is added since the single period in line 11 indicates the end of the lines to be added In line 9 refers to the last line of the file being edited that is the text in line 10 has to be added after the last line In ed as in vi command line mode refers to the last line of the file being edited The backslash is the shell quote character this means that the dollar sign in line 9 is quoted as far as the shell is concerned the shell strips the quote character and ed will receive only a instead of the present form of line 9 If we had written a for line 9 that is if it had been written without the quote character then the shell would have interpreted a as indicating the value of a shell variable if this variable is not defined as is likely to be the case at present this value will be the empty string and ed would receive the empty string in line 9 instead of a Lines 12 14 add the content of line
225. uld type file homedirectory netscape bookmarks dir bookmarks5 html in the window just opened where homedirectory should be replaced with the absolute path to your home directory E g if your login name is cmuser your home directory may be home cmuser In this case you should type file home cmuser netscape bookmarks dir bookmarks5 html Note that the slash after file is part of the absolute location of the file By the way you should save this location as a bookmark You may not like the name Netscape assigns to this bookmark in this case you may edit the bookmarks html file located in the Netscape directory manually i e by using say the vi editor to give the name bookmarksd to this location it is best to do this while Netscape is not open Afterwards Netscape might complain that the bookmarks have been changed but apparently you can safely ignore this annoying complaint Netscape crashes Sooner or later Netscape will crash on you that is it will close unexpectedly When you next try to open it it will give you a message saying that Netscape is already running You are then offered to open a version of Netscape that is not fully functional most likely it will not be able to use its cache a directory where items such as files describing picture from recently visited Web sites are stored Rather than using such a dysfunctional version of Netscape quit Netscape remove the file called lock in the netscape directory
226. un as the command email cmuser5 The first argument here was cmuser The arguments used on the command line when running the shell script can be referred to inside the shell script as 0 1 2 0 refers to argument number 0 which is the name of the command itself email at present and the others are the successive arguments used Since only one argument was used the arguments 2 3 4 will at present be undefined within the shell script actually their value will be the empty string It is important to note that the aliases in mailrc are not understood in line 2 those contained in the argument 1 cmuser5 at present are understood so one can still use mail aliases in the letter to be sent out In line 3 the command cat appends the content of the file HOME marks sentmark at the end of the file described 1 which as we indicated above at present means the file cmuser5 Here the symbol gt gt is obtained just by typing two gt symbols Furthermore HOME is a shell variable that refers to the users home directory Tech nically the name of this variable is HOME by writing HOME the value of this shell variable is indicated in any case HOME will expand to something like home jsmith or whatever is used as the home directory of a user having say jsmith as login name The directory HOME marks that is say home jsmith marks has to be created and in this directory a file called sentmark needs to be created with t
227. unki pascal secl tex sec2 tex sec3 tex sec4 tex seco tex As you can see here filenames can contain letters upper or lower case numbers and various other characters such as period and underscore _ The reason to use filenames such as junk or junk1 is that you will know that these are not very important files needed only temporarily You can use the command 1s in different ways for example typing 1s F will give edg euclid_new p junk junki pascal secl tex sec2 tex sec3 tex sec4 tex seco tex Here the asterisk after edg means that edg is an executable file the slash after pascal means that pascal is a directory There is much more to the command 1s You can find out more about it by looking up the on line manual page on it by typing man ls Initially the information you receive is more than overwhelming If you really want to read it you can scroll down by hitting the space bar scroll backwards by pressing the letter b and advance a single line by pressing the enter key also called return key At this point the best choice may be to quit trying to read the information presented you can do this by pressing the letter q In any case as you learn more about Unix you will find the on line manual pages very helpful if somewhat terse If you want to actually see what is in a file you might try to do this by typing cat edg This is safe to do only if you know that the file called edg is in fact an ascii file
228. ussed it is much like a decimal fraction written in scientific notation e g 2 3798 107 but we will not give the precise definition here division by zero will result in an error div for integer division that is the quotient resulting from the division of two integers is given and the remainder is discarded the result is an integer for a precise definition one needs to carefully discuss the case when one or both of the operands are negative but we will not be interested in that case divi sion by zero will result in an error mod gives the remainder of the division of two integers again special explanations must be given if one or both of the operands are negative division by zero is again not allowed The rules for evaluating arithmetic expressions are much the same as in mathematics For example the expression 4 2 3 3 2 is evaluated to be 26 since the sum 2 3 in parenthesis has to be evaluated first giving 5 then 4 5 makes 20 next the multiplication 3 2 must be evaluated giving 6 before the addition since multiplication has priority over addition finally the two partial results 20 and 6 must be added resulting in 26 In line 7 the write statement is new It works exactly like the writeln statement except that it does not print an end of line character i e it does not start a new line after finishing printing The program will print the following line The sum of 15 and 12 is 27 If we change line 8 to write
229. ve If two instances of viewhtml are run at the same time and from the same working directory the script can get confused since both of them try use the same filename junknetscape Fortunately it is fairly easy to resolve this problem In Unix the instance of a running program is called a process We use the word instance since in Unix the same program can be run simultaneously several times and each of these runs or instances is called a process Each process is assigned a unique number called process id or PID In a shell script the shell vari able has the value of the the process id of the shell current instance of running the shell script This can be used to generate unique filenames Instead of the filename junknetscape in the above shell script viewhtml we can use the filename junknetscape If we run viewhtml and the process id of the current instance viewhtml is say 1364 then this filename will be resolved as junknetscape1364 and so it will be unique to the current instance of viewhtml Here is the improved version of viewhmt1 called say viewhtm10 using this idea bin sh NN file HOME html_files 1 rm f junknetscape gt amp dev null touch junknetscape ed junknetscape lt lt j Oa netscape remote openURL NN new window e OANA OF WN W the command junknetscape will be executed while the command junknetscape will not see p 98 21 There are safer ways
230. ven if instead of lines 18 and 19 we would have written b and c such that a7n b n c n or for that matter b and c such that a n b n c n The reason we put the formula in line 19 in a line by itself because this makes it easier to read the tex file After some practice it is possible to learn how to read a tex file without typesetting it and this allows one to work much faster However in order to read the tex file fast it is important to format the tex file properly even if formating has no effect on the typeset file The situation is somewhat similar with the use of indentation in Pascal programs indentation has no effect on the way the program runs but it is useful for people wanting to read the program The difference is that there are fairly strict rules on how to indent a Pascal program whereas there are really no accepted rules as to how to format a tex file In the formula in line 19 the caret symbol introduces superscripts exponents Thus a n is printed as a Subscripts are introduced by underscore _ Thus to typeset ag one needs to type a_2 Double superscripts are not allowed so one cannot type 373 3 In order to typeset 33 one needs to type 37 373 that is the delimiters and must be used to keep things together In line 25 the control sequence it indicates italics type font the effect of this control sequence is confined between the delimiters and Slanted typeface is indi
231. visors of both of them For example the divisors of 12 are 1 2 3 4 6 12 The divisors of 18 are 1 2 3 6 9 18 Thus the common divisors of 12 and 18 are 1 2 3 6 The greatest among these is perhaps unsurprisingly called the greatest common divisor of 12 and 18 The usual mathematical notation for the greatest common divisor of two integers a and b are denoted by a b Hence 12 18 6 The greatest common divisor is important for many reasons For example it can be used to calculate the least common multiple of two numbers i e the smallest positive integer that is a multiple of these numbers The least common multiple of the numbers a and b can be calculated as a b For example the least common multiple of 12 and 18 is 12 18 12 18 12 18 6 Note that in order to calculate the right hand side here it would be counter productive to multiply 12 and 18 together It is much easier to do the calculation as follows Bi ig 8 a Pg ae 6 6 18 13 THE EUCLIDEAN ALGORITHM 53 That is the least common multiple of 12 and 18 is 36 It is important to know the least common multiple when adding two fractions For example noting that 12 3 36 and 18 2 36 we have 5 7 5 3 7 2 15 14_ 15414 _ 29 12 18 12 3 18 2 36 36 36 36 Note that this way of calculating the least common multiple works only for two numbers We will not discuss the case of more than two numbers our main interest here is the greatest c
232. will be merged into a single product called Windows 2000 Unix is more properly compared to Windows NT than the less sophisticated Windows 98 There are several articles devoted to comparing Unix and Windows NT for example see http www unix vs nt org kirch An interesting sideline of the comparison between Unix and various Microsoft operating systems is the recent antitrust trial of the US Department of Justice and nineteen states vs Microsoft The judge s finding of facts concluding the first phase of the trial can be found at the site http usvms gpo gov findfact html and at the site in HTML with links to various parts to of the documents plus download links to various formats e g PDF that is Adobe s Portable Document Format http www usdoj gov atr cases f3800 ms judgex htm The site http www seattletimes com news technology htm198 mono_19991106 html the site address was scrolled over to the next line but when entering it into your browser the line must not be broken up which appeared in the Seattle Times gives an interesting legal analysis of the ruling Logging in In order to use a computer using Unix you need a login name and you need a password The login name will often be an abbreviation of your name and it should consist of all lower case letter The password will usually have 8 12 letters and it is often required that it should contain a mixture of upper and lower case letter numbers and non letter
233. window will still open but the prompt will not be returned in the original window There are several ways to remedy this situation First one can type exit in the new window This will close the window The same effect can be achieved by typing Ctl c i e holding down the control key and typing c at the same time in the original window i e in the window in which the command xterm was typed Ctl c usually kills terminates a running program although not every program will respond to Ctl c As the third action one can stop the program by typing Ctl z The computer will respond with something like this 2 Stopped xterm Here 2 indicates the number of the job refers to the current job and refers to the previous job One can restart this job in the foreground by typing fg 42 there would be little purpose of doing this since the program was running in the foreground before it was stopped and it was undesirable to have xterm running in the foreground Instead one can restart this job in the background by typing bg 2 This is the proper solution and its effect is the same as if the program xterm had been started in the background in the first place To check which jobs run in the background one can type jobs The answer might something like 1 Running netscape amp 2 Stopped xterm 3 Running xterm amp The ampersand amp at the end of the line indicates that the program is running in the background One can
234. y knowledge the letter has not been published in 49 the London Times 50 You may prefer to read a discussion of the London 51 Sunday Times article first To do this 52 lt A HREF http www ssc com linux suntimes 53 gt click here lt A gt 54 This discussion has links both to the original 55 article and to my letter 56 You can also go directly to the 57 lt A HREF 58 http www the times co uk news pages sti 97 04 20 st iinnsnd01001 htm1 1007000 gt The Times Internet Edition lt a gt 59 to read the original article first then come back 60 here to follow the links to the discussion and to 61 my letter 62 lt P gt 63 lt BR gt 64 Last updated 65 Wed Jul 22 10 06 03 EDT 1998 66 lt BODY gt 67 lt HTML gt First note that the numbers on the left are line numbers and they are not part of the file We included them for easy reference In particular line 44 is longer than can be displayed in the editor window and so it is wrapped around broken up in the display but the continuing part does not receive a new line number since since it does not constitute a new line in the logical sense To understand HTML first note that the text to be displayed is interspersed with short strings of symbols intended to control the way the text is displayed these strings of symbols are called HTML tags We will discuss the tags occurring in the above text A systematic list of other tags can easily be found on the World Wi
235. y typing Mail instead In Linux you may also try mail n which inhibits the reading of the file etc mail rc since the unwanted behavior of the mail program may be caused by the content of this file This latter command does not work in all versions of Unix 22 ELECTRONIC MAIL 87 3 etc and indicating who the mail is from and the subject of the email which is specified by the sender see below Then the mail program gives you a prompt amp here O indicates the cursor We used amp for the mail prompt but sometimes other symbols are used often gt is the mail prompt If you are not interested in reading the letters now you can type amp x that is you type x amp is the mail prompt this will exit the mail program x is for exit without doing anything you can come back and read the letters at a later date If you want to read say the 2nd letter you can type amp 2 Sometimes you receive a long letter you can scroll down in this letter by pressing the space bar or the return key the former usually scrolls by a whole window content while the latter only scrolls down a single line If the letter is too long and you do not want to read it all the way you can quit reading it by typing q you have to be careful however because you do not want to type q after the letter scrolled down all the way since this will cause the mail program to quit see below You can tell whether or not this is the case when the l
236. y word program 38 key word readin 43 key word reset 58 key word text 93 INDEX key word var 40 42 key word write 42 93 key word writeln 38 40 42 loops in 44 47 operators in arithmetic 42 logical 70 71 ordinal type in 73 output in 38 packed character in 73 program documenting of 51 for email sentmark 93 tracing of 45 truth tables for 69 72 program heading 38 reading from a file 58 real type in 42 repeat statement in 70 reserved word see Pas cal word symbol running programs 38 semicolon in 41 separator in 38 statement in 38 compound 44 conditional 48 51 if 49 type in 40 variable in 40 versions of see GNU Pascal and Sun Pascal while do statement in 44 word symbol 38 writeln widths of fields 46 Pascal Blaise 36 password 7 changing 8 PATH shell variable see shell variable PATH Perl 91 119 139 permission codes 17 18 Personal Identification Num ber see PIN number PID see process id pidof to find out process id 107 PIN number in file names 29 pipe in Unix 88 105 pixel 32 Plain TeX see TeX Plain Pope Gregory XIII see Gre gory XIII Pope portability of programs see program portability of porting programs 38 PostScript 30 79 viewer see ghostview pound sign 122 ppp 127 previewing TEX see TRX previewing prime factorization 67 uniqueness of 67 prime number 67 print working directory see directory print working pr
237. ype i for insert after the current cursor position type a for add To go into insert mode below the current line so as to insert a new line type o and above the current line type 0 When in command mode it is especially important not to press the capitals lock key accidentally Unix is case sensitive and the above commands have completely different meanings in upper case than in lower case and typing a few capital letters in command mode instead of the intended lower case letters can cause serious damage to the file If you make a mistake you can correct it by typing u when in command mode This will take you back to the version of the file before the last change was made 3In Unix the line feed character LF decimal ascii code 10 is used to break lines The Macintosh operating system uses the carriage return character CR decimal ascii code 13 for this and Windows uses CR and LF together 4The editor vi behaves differently in Sun Unix and in Linux In Sun Unix typing u toggles between the current and the preceding version of the file that is typing u twice takes you back to the current version In Linux typing u two or more times takes you to yet earlier versions of the file To get back to the current version you have to type Ctrl r the same number of times as you typed u 14 I UNIX Command line mode When typing a colon in command mode the colon will appear at the bottom of the screen and t

Here - Computer and Information Science

Contents

Download Pdf Manuals

Related Search

Related Contents