quash

Quite a Shell (quash)

Project No. 1: Quite a Shell (quash) Submission due: Oct. 10, 2014 PURPOSE ● Getting familiar with the Operating System (UNIX) interface. ● Exercising UNIX system calls. ● Understanding the concept of process from the user point of view. DESCRIPTION In this project, you will implement Quite a Shell (quash) using the UNIX system calls. You may work in groups of 2 if you choose. Quash should behave similar to csh, bash or other popular shell programs. Specifically, the following features should be implemented in quash. ● Quash should be able to run executables (the basic function of a shell) with command line parameters ● If the executable is not specified in the absolute path format (starting with ‘/’), quash should search the directories in the environment variable PATH (see below). If no executable file is found, quash should print an error message. ● Quash should allow both foreground and background executions. Character ‘&’ is used to indicate background execution. Commands without ‘&’ are assumed to run in foreground ○ When a command is run in the background, quash should print: [JOBID] PID running in background ○ When a background command finishes, quash should print: [JOBID] PID finished COMMAND ● Quash should support the following built­in functions: ○ set to set the value of a variable in the environment. Quash should inherit the initial environment from the command line that invokes it. In C, this is achieved by using the charenvpargument to main, as in: intmain(intargc,charargv,char**envp) Quash should support (at least) two built­in variables: PATH, which is used to record the paths to search for executables, and HOME, the user’s home directory. PATHmay contain multiple directories (separated by :). For example, The command ‘setPATH=/usr/bin:/bin’ in quash should set the variable PATHto contain two directories, /usr/binand/bin. Note that Child processes should inherit the environment variables (in C, various flavors of the exec system call allow you to pass the environment to child processes) ○ cd

to change the current working directory to dir. cd with no arguments should change to the directory in the HOME environment variable.○ quit and exit to exit quash. ○ jobs should print all of the currently running background processes in the format: [JOBID] PID COMMAND where JOBID is a unique positive integer quash assigns to the job to identify it, PID is the PID of the child process used for the job, and COMMAND is the command used to invoke the job. ● Quash should implement I/O redirection. The ‘<’ character is used to redirect the standard input from a file. The ‘>’ character is used to redirect the standard output to a file. For example, ‘ls>a.txt’ sends to results of ls to file a.txt ● Quash should implement the pipe (|) command. e.g. ‘catmyprog.c|more’ ● Quash should support reading commands interactively (with a prompt) or reading a set of commands stored in a file that is redirected from standard input, as in: bash>quash<commands.txt

GRADING POLICY Partial credits will be given for incomplete efforts. However, a program that cannot compile will get 0 points. Point breakdown for features is below:

1. Run executables without arguments (10)
2. Run executables with arguments (10)
3. set for HOME and PATH work properly (5)
4. exit and quit work properly (5)
5. cd (with and without arguments) works properly (5)
6. PATH works properly. Give error messages when the executable is not found (10)
7. Child processes inherit the environment (5)
8. Allow background/foreground execution (&) (5)
9. Printing/reporting of background processes, (including the jobs command) (10)
10. Allow file redirection (> and <) (5)
11. Allow (1) pipe (|) (10)
12. Supports reading commands from prompt and from file (10)
13. Report (10)
14. Bonus points (you can get bonus points only if you have everything else working (or very close to working)) a. Support multiple pipes in one command. (10) b. kill command delivers signals to background processes. The kill command has the format: killSIGNUMJOBID, where SIGNUM is an integer specifying the signal number, and JOBID is an integer that specifies the job that should receive the signal. (5)SUBMISSION Each group should submit the project by email to the TA ([email protected]). Create a tar file with all of your source code and a Makefile and build instructions. The report should describe each of the features in your quash shell and (briefly) how you implemented each feature. Also, describe how you tested quash and document any required features that are not completely implemented in your quash shell. MISCELLANEOUS ● This project is not so easy to implement. Start early! ● You need to use C language to implment this project.