Shell

A simple UNIX-style shell implemented in C.

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Features

• Keeps a few list of built-commands to run such as exit, ?, pwd and cd
• Executes external programs by searching for executables PATH environment variable
• Supports input and output redirection for external commands (e.g wc < textfile > outputfile)
• Supports pipelined commands (e.g wc shell.c shell.c shell.c | grep total)
• Supports running processes in the background

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Build Instructions

make

Running make produces the shell executable in the current directory

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Usage

Start the shell:

./shell

Example interactive session:

Built-in commands:

0: ?  
? - show this help menu
exit - exit the command shell
pwd - prints the current working directory
cd - changes the current working directory
wait - block until all background jobs have terminated
1: pwd
/home/mubaaroq/Desktop/systems/hw-shell
2: cd ..
3: pwd
/home/mubaaroq/Desktop/systems/

Executing external programs:

0: wc shell.c
 295 1055 7825 shell.c
1: ls /home/mubaaroq
 Desktop  Documents  Downloads  Music  Pictures	Public	snap  Templates  Videos

Pipeline commands and input/output redirection:

0: wc shell.c shell.c shell.c | cat | grep total
 885  3165 23475 total
1: wc < shell.c > test_out
2: cat test_out
 295 1055 7825

Executing commands in foreground or background:

0: sleep 20 | sleep 30
^C1: 
2: sleep 20 | sleep 30 &  
3: ps -o pid,pgid,wchan,cmd
    PID    PGID WCHAN  CMD
   5392    5392 do_wai bash
   6029    6029 do_wai ./shell
   6079    6079 hrtime sleep 20
   6080    6079 hrtime sleep 30
   6081    6081 -      ps -o pid,pgid,wchan,cmd
4: wait
5: ps -o pid,pgid,wchan,cmd
    PID    PGID WCHAN  CMD
   5392    5392 do_wai bash
   6029    6029 do_wai ./shell
   6095    6095 -      ps -o pid,pgid,wchan,cmd

Credits / Acknowledgements

• Based on skeleton code from UC Berkeley CS162 coursework