/kavach-shell-OS

A simple shell interpreter for demonstrating the use of process control and inter-process communication system calls on UNIX like systems

Primary LanguageC

Shell interpreter (Operating Systems)

MIS : 111703041

Name : Bhaskar Pardeshi

Year : TY

Input redirection

  • Usage : cmd <infile
  • If multiple input files are given to the same program than the last file is taken into consideration, i.e. cmd <infile1 <infile2 <infile3, here infile3 will be used to redirect the input

Output redirection

  • Usage : cmd >outfile
  • If multiple output files are given to the same program than the last file is taken into consideration, i.e. cmd >outfile1 >outfile2 >outfile3, here outfile3 will be used to redirect the output

Pipes

  • Usage : cmd (<infile)* (>outfile)* (| cmd (<infile)* (>outfile)) (Its funny how, I have written a grammar using regular expression)
  • Multiple pipes are supported in this shell

Background process

  • Usage : (cmd) &
  • Specifying & at the very end of the (piped) command will move the cmd to the background
  • & is not supported in between (potential update)

Signal handling

  • It is made sure that the signals are directed to foreground process group only (as the fork-execed process form a new group every time)

  • SIGINT

    • Pressing ctrl-c while in prompt prints new prompt
    • Pressing ctrl-c while in command execution will terminate the command

  • SIGTSTP

    • Pressing ctrl-z while in prompt ignores the signal
    • Pressing ctrl-z while in command execution will suspend the command

  • Few more signals (SIGCHLD, SIGCONT, SIGTTOU, SIGTTIN) are used

Job handling

  • The process groups can be switched to foreground if suspended or in background using the command. Specifying pid of a process will move the group in which that pid lies to the foreground of the controlling terminal
  • The process groups can be switched to background if suspended using the command. Specifying pid of process will move the group in which the pid lies to the background
  • The suspended or background process groups can be viewed using command

Built-ins

  • cd (change directory)
  • fg (foreground switch)
  • bg (background switch)
  • jobs (print jobs)

Miscellaneous

  • Pressing ctrl-d on blank prompt will exit the shell program
  • Error handling is not so good
  • Its completely colorless shell (as systems people should never enter the darkness of UI)
  • The shell is named "kavach"