Description
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 (5 point) ● 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 example) $ program1 & [1] 2342 → job id = 1, pid = 2342 ○ When a background command finishes, quash should print: [JOBID] PID finished COMMAND example) [1] 2342 finished program1 ● Quash should support the following builtin functions: ○ set to set the value of a variable. Quash should support (at least) two builtin variables: PATHandHOME.PATHis used to record the paths to search for executables, while HOME points the user’s home directory. PATHmay contain multiple directories (separated by :). example) $ setPATH=/usr/bin:/bin → set the variable PATHto contain two directories, /usr/binand/bin. $ set HOME=/home/amir → set the user’s home directory as ‘/users/amir’ echo should also be implemented to print the content of the PATH and HOME. The format for echo is as same as bash. As an example $ echo $PATH →/usr/bin:/bin ○ cd
to change the current working directory to dir. if no argument is given, it should change to the directory in the HOME environment variable. example) $ cd test → change the current working directory to ./test $ cd → change the current working directory to $HOME directory ○ pwdprint the absolute path of the current working directory example) $ mkdir test $ cd test $ pwd /home/amir/test ○ quitand exitto exit quash. example) $ quit bye ○ jobsshould 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. example) $ program1 & $ program2 & $ jobs [1] 2342 program1 [2] 2343 program2 ● 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. example) $ls>a.txt’ → store the results of ls to file a.txt ● Quash should implement the pipe (|) command. example) $ 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. example) $./quash and <) (10) 11. Allow (1) pipe (|) (10) 12. Report (10) 13. Bonus points a. Support multiple pipes in one command. (10) $ ls | wc | more 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 to your TA via Blackboard. Create a zip file of your code using “make submit”. You should also check that the zipped project still builds and runs correctly after building the submit target with “make unsubmit”. Your TA will be using this command to extract and build your project so make sure it works correctly. If you modify either of these targets, please ensure all file extensions are renamed to “.txt” in the submission and extract correctly with the unsubmit target. 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 ● Start early! ● You need to use C language to implement this project.
