CS 3204
Contents
1. be posted on the course web site You will be allowed to submit your project up to three times before the due date in order to fix errors you discover before your project is tested Your latest submission will be the one that is tested Pledge Your program submission must be pledged to conform to the Honor Code requirements for this course Specifically you must include the pledge statement provided on the Programming Standards page in one of your submitted files 9 5 2005 11 55 AM page 42. CS 3204 Capra section Project 1 Fall 2005 Command Shell The shell or command line interpreter is a fundamental user interface to an operating system Your first project is to write a simple shell called myshe11 that has the following properties The shell will loop continuously to accept user commands it will terminate when quit is entered The command line prompt must contain the pathname of the current directory Internal commands The shell must support the following internal commands Internal commands should be handled by the ed lt pathname gt lt directory gt Change the current default directory to lt directory gt If the lt directory gt is not present report the current directory If the directory does not exist an appropriate error message should be reported The command should also change the PwD environment variable clr Clear the screen dir lt pathname gt lt directory gt List the contents of lt directory gt Ifthe lt directory gt is not present list the contents of the current directory If the directory does not exist an appropriate error message should be reported environ List all the environment strings echo lt string gt Display lt string gt on the display followed by a new line help myshell Display the user manual as a man page Note that you must use the nroff markup language and standard Unix man page format for this You will not be able to install your page
3. ere are many good online C C language references 9 5 2005 11 55 AM page 3 CS 3204 Capra section Project 1 Fall 2005 Evaluation Remember that your implement will be tested in the McBryde 124 lab environment GCC Linux No help will be given for any other development environments It is your responsibility to make sure your implementation works correctly in the lab Your implementation will be evaluated for documentation and design as well as for correctness of results Note that the evaluation of your project may depend substantially on the quality of your code and documentation What to turn in and how This assignment will be collected on the Curator system The testing will be done under the McBryde 124 lab environment Submit a single gzip d tar file containing the C C source and header files for your implementation to the Curator system Submit only the source and header files Submit nothing else Be sure that your header files only contain include directives for Standard C C and UNIX header files any other include directives will probably cause compilation errors It must be possible to unpack the file you submit using the following command tar zxf lt name of your file gt The unpacked files will then be compiled typically using the following command syntax g gcc o lt name we give the executable gt cpp c Instructions and the appropriate link for submitting to the Curator system will
4. hat contains the entry parent lt pathname gt myshell Upon finding the executable the shell will echo the full path from the system root to the directory where the executable was found If the executable is not found the shell will issue an informative error message Path specifications When appropriate the user may include path specifications in commands as indicated by lt pathname gt in the internal command specifications above and elsewhere The shell will accept path specifications that start with and However the user should not be required to include path specifications In a program invocation when no explicit path is given to an executable the shell will search for the executable according to the values in the environment variable PATH This value must be retrieved using the UNIX system call getenv The shell environment should contain shel1l lt pathname gt myshell where lt pathname gt myshell is the full path for the shell executable not a hardwired path back to your directory but the path from which it was executed Other considerations The shell must take into account the attributes of relevant files For example if the command usr home me foo is entered and the specified file exists in the specified location but is not executable the shell will issue an informative error message The shell must be able to take its command line input from a file i e if the shell is invoked
5. into the man facility but the help command should display it using the nroff processor i e You should not simply format a text file to look like a man page you must use the nroff markup language There are many resources on the web about how to write man pages An on line article from the CS Department at Harvey Mudd College at lt http www cs hmc edu qref writing_man_pages html gt may provide a good starting point pause Pause operation of the shell until the enter key is pressed Sets a shell variable lt varname gt to the value lt value gt Both lt varname gt and lt value gt may consist of a string of case sensitive alphanumeric characters A Za z and 0 9 and each may be up to 32 characters long Your shell should allow the creation of at least 255 distinct shell variables Shell variables should be able to be used as part of any lt string gt lt pathname gt lt directory gt or lt value gt When using a shell variable as part of a lt string gt lt pathname gt lt directory gt or lt value gt the effect should be that the variable is replaced with its corresponding value quit Quit the shell 9 5 2005 11 55 AM page 1 CS 3204 Capra section Project 1 Fall 2005 Program invocations All the other command line input is interpreted as program invocation which should be done by the shell forking and executing the program as its own child processes The programs should be executed with an environment t
6. nching that program 9 5 2005 11 55 AM page 2 CS 3204 Capra section Project 1 Fall 2005 Changes to shell environment variables should be registered using setenv or putenv so those values will be visible when external program invocations are made When your shell exits the environment should be restored to the same state as before the shell was started User documentation You must write a simple user manual describing how to use the shell The manual should contain enough detail for a UNIX beginner to use it For example you should explain the concepts of I O redirection the program environment and background program execution Your manual should be formatted in the standard UNIX man page format and be written using the nroff markup language as described earlier in this document For an example of the sort of depth and type of description required you should take a look at the online manuals for one or more of the common UNIX shells csh tcsh etc Those shells are much more complex than yours will be so your manual does not need to be so large The user manual should not contain build instructions an included file list or source code The purpose of the manual is to be for end users not shell developers Design and implementation requirements There are some explicit requirements in addition to those on the Programming Style page of the course website e Your shell must be implemented in ISO compliant C C code Yo
7. u may make use of any language standard types and or containers you find useful e You must decompose your implementation into separate source and header files in some sensible manner that reflects the logical purpose of the various components of your design e You must document your implementation according to the Programming Standards page on the course website e You must properly allocate and de allocate memory as needed e If your shell does not implement a specified feature it should write an appropriate disclaimer when the user attempts to use that feature something distinguishable from a normal error message resulting from a logically invalid command Any such omissions should also be documented in the User Manual In general you are expected to apply the design and implementation guidelines and skills covered in your previous computer science courses You may implement your solution in pure C or in C Suggestions and assumptions There are some explicit assumptions you may make e No command line will be longer than 100 characters and no command will be given more than 10 arguments not counting redirections and e Each command argument redirection symbol and amp will be preceded by at least one blank space You may find it helpful to consult the UNIX man pages on fork exec getenv access and waitpid You may also find it helpful to look up the C library function freopen Note that th
8. with a command line argument myshell lt batchfile then bat chfile is assumed to contain a set of command lines for the shell to process When the end of file is reached the shell should exit If the shell is invoked without a command line argument it solicits input from the user via a prompt on the display The shell must support I O redirection on either or both stdin and stdout That is the command line programmname argl arg2 lt inputfile gt outputfile Will execute the program programname with arguments arg1 and arg2 the stdin file stream replaced by input file and the stdout replaced by output file stdout redirection should also be possible for the internal commands dir environ echo and help With output redirection if the redirection token is gt then the output file is created if it does not exist and truncated if it does and its write permissions are set If the redirection token is gt gt then the output file is created if it does not exist and appended if it does When an output file is created using redirection its access permission must at least include read permission for the owner If redirection targets an existing file whose write permissions are not set the shell will issue an informative error message The shell must support background execution of programs An ampersand amp at the end of a command line indicates that the shell should return to the command prompt immediately after lau
Download Pdf Manuals
Related Search