Basic shell

Basic shell with job control. It offers the most basic functionality of a linux shell, a program that allows the execution of processes. Processes can be interrupted, continued, and executed on the background.

📌 Summary explanation.

Compilation

Clone the repo and launch makefile.

$ make

Alternatively, compile as:

$ gcc -o shell -Wall src/main.c src/signals.c src/jobs.c src/wrappers.c

An executable shell will be generated.

Features

• Runs executables in the current working directory or the specified path.
• Runs one process in the foreground or several in the background.
• The foreground job can be terminated by typing Ctrl+C and stopped by typing Ctrl+Z.
• Built-in commands: fg, bg, jobs, and quit.
  • fg <id>: send the process specified by <id> to the foreground.
  • bg <id>: send the process specified by <id> to the background.
  • jobs: displays a list of currently active jobs.
  • quit: terminate the shell.
• Processes can be identified by a process id (PID) or a job id (JID) preceded by %.

> bg %1      // Resume job with JID=1
> bg 14501   // Resume job with PID=14501

• Exit shell by pressing Ctrl+D or typing quit.

Example shell session

For this demo, wait and write are dummy executables present on the current working directory that run in an infinite loop. The ^C and ^Z characters below are the result of typing Ctrl+C and Ctrl+Z.

$ ./shell
> ls
ls: Command not found.
> /bin/ls
jobs.c	 jobs.h   main.c   Makefile   README.md  signals.c   signals.h	wrappers.c   wrappers.h   write
jobs.c~  jobs.h~  main.c~  Makefile~  shell	 signals.c~  wait	wrappers.c~  wrappers.h~
> wait &
[1] 17715			wait &
> wait
^Z
Job [2] 17716 stopped by signal: Stopped
> fg %2
^C
Job [2] 17716 terminated by signal: Interrupt
> write
1...
1...
1...
1...
^C
Job [2] 17718 terminated by signal: Interrupt
> wait &
[2] 17719			wait &
> jobs
[1] 17715 Running		wait  &
[2] 17719 Running		wait  &
> quit

Sources

• Core read-eval loop taken from CS:APP.
• Helper wrapper functions taken from csapp.c.

License

MIT