Shell

A linux shell written in C language to implement various shell commands.

Make Instructions:

• Run make to create shell executable.
• Run ./shell to run the shell.

File Breakdown:

• init.c: Contains functions for displaying the output and to split semi-colon separated commands.
• shell.c: Contains functions to implement commands.
• bg.c: Contains functions to implement background processes and bring stopped background process to running background process.
• fg.c: Contains functions to implement foreground processes that are not built-in commands and send foreground process to stopped background process.
• headers.h: Contains headers, function declarations and variable declarations.
• random.c: Contains some random functions like to remove an extra line and all.
• cd.c: Contains functions to implement cd command.
• pwd.c: Contains function to implement pwd command.
• echo.c : Contains function to implement echo command.
• pinfo.c: Contains functions to implement pinfo command.
• ls.c: Contains functions to implement ls, ls -l, ls -al, etc. commands.
• handler.c: Contains functions to display exit status of background process.
• signals.c : Contains user defined signal handlers.
• delete.c : Contains function to delete the background job that has been killed from jobs structure.
• env.c : Contains functions to set and unset an environment variable.
• jobs.c : Contains functions to list all the background processes with their state and pid.
• overkill.c : Contains function to kill all the background processes at once.
• pipe.c : Contains function to implement piping commands.
• redirection.c : Contains function to implement I/O redirection.
• redirect.c : Contains function to I/O redirection + pipes redirection.
• kill.c : Contains function to send a signal value to a process whose id is known.

Features:

• Shell supports built-in commands like cd, pwd, echo, etc.
• Shell supports semi-colon separated list of commands.
• Shell supports '&' operator which lets a program run in background and displays a proper message when it exits.
• Shell supports many manually defined commands like jobs, kjob, fg, bg, overkill, Ctrl + Z and Ctrl + C.
• Errors are handled properly.

Commands:

• cd [directory] : Changes current working directory to the directory specified.
• pwd : Displays the name of current working directory.

• echo [arguments] :
  • Displays whatever is specified in [arguments].
  • Displays the value of environment variable(ex. $USER).
• pinfo <pid> :
  • Displays process info such as status, memory and executable path about given pid.
  • If no arguments, displays details of the shell.

• ls [-l -a] [directory] : Lists all the files and directories in the specified directory.
• bg <job number> : Changes a stopped background job with given job number to a running background job.
• fg <job number> : Brings a running or a stopped background job with given job number to foreground.
• setenv var[value] : Creates environment variable var if it does not exist and sets value of var to value.
• unsetenv var : Destroys the environment variable var.
• jobs : Prints a list of all background jobs(Running or Stopped) with their pid.
• kjob <job number> <signal number> : Sends a signal value to a running process with the given job number.
• overkill : Kills all background process at once.
• quit : Exits the shell.
• Ctrl-Z : Changes the status of currently running job to stop, and pushes it to the background.
• Ctrl-C : Sends SIGINT signal to the current foreground job of the shell.