/yashell

Linux C shell

Primary LanguageC

Yet Another SHell

Assumptions

  • max length of username is 32 chars
  • max number of arguments + flags in a command is 10
  • max length of hostname is 64
  • max length of a path is 256
  • max children spawned from the process is 16 (to simplify the program, although it is easily scalable by using linked lists)
  • max length of a command is 256 chars
  • all these can be changed at a single place and will reflect throughout the code

Features

  • Shows a prompt, which has username, hostname and the path, relative to the directory where the shell executable is located.

  • cd

    • cd and cd ~ change the cwd to the directory where the executable lives

  • ls

    • recognizes -l and -a flags

  • echo, pwd implemented

  • I/O redirection:

    • >
    • >>
    • <
    • one of > and >> is allowed. If both are passed, > is given priority and >> will be ignored.

  • Piping

  • Piping+redirection

    • caution: if multiple commands are piped, input redirection is allowed only in the first command, and one of output/append is allowed in the last piped command. No other scenario is allowed wrt redirection-within-piping.

  • Foreground and Background process launching, zombie process handling and reaping

  • Self implemented commands:

    • pinfo: prints info about a process
    • repeat: repeats whatever was given as arguments
    • job: recognises -r and -s flags, lists jobs which are running and sleeping respectively. These jobs are sorted in lexicographical order
    • sig: send a signal to any job that was launched via YAShell
    • fg: brings the running or stopped background job to the foreground and changes its state to running.
    • bg: makes a stopped background job to running background job

  • Signal handling:

    • Interrupt signal (Ctrl + C) to a forground job. Does not kill YAShell.
    • Stop Signal (Ctrl + Z) pushes a foreground job to background and pauses its execution

  • Exiting the shell:

    • Ctrl + D logs you out and bash/zsh/fish/whateversh comes back

  • Return status: like the usual Bash/zsh shell prompt, return status of the previous command is shown. :-) in green if it returned 0, :-( in red otherwise.

Execution

make shell will give an executable shell in your terminal, run ./shell

To delete the executable, make clean