C-Shell

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A Shell written in C. This is a project for my Operating Systems class. The goal is to create a user-defined interactive shell program that can create and manage new processes. It will also be able to handle input/output redirection and piping, and will be able to run in the background.

It has the following features:

• Shell Prompt user@host:~/dir$ contains the username, hostname, and the invoking directory as the home directory. Supports full path names that are outside of the home directory.

• Built-in Commands (without using execvp)

  • cd <dir>: Changes the current directory to <dir>

    • cd changes to the home directory
    • cd - changes to the previous directory

  • pwd prints the current directory

  • echo prints the arguments

  • ls [-al] <dir> lists the contents of the directory - argument dir prints the contents of the directory - -l long listing format with file size, permissions, owner, group, date modified, file name and symbolic link - -a shows hidden files

• External Commands (using execvp) with background execution ( & ) and show when a background process is finished similar to bash.

• Input/Output Redirection

  • > redirects the output of a command to a file
  • < redirects the input of a command from a file
  • >> appends the output of a command to a file
  • Shows an error if the file does not exist

• Piping

  • | pipes the output of one command to the input of another command
  • Supports multiple pipes
  • Supports redirection with pipes

• User defined commands

  • pinfo prints the process id, process status, memory, and executable path of the shell or the process id given as an argument

  • nightswatch [-n] <command> Modified version of watch that prints the output of the command every n seconds. n is 2 seconds by default.

    • -n specifies the number of seconds to wait between updates
    • command can be interrupt or newborn
      • interrupt prints the number of interrupts CPU(s) have been interrupted by the keyboard since boot
      • newborn prints the PID of the most recently created process

  • history <n> prints the last 10 or n commands entered by the user

  • setenv <var> <value> sets the environment variable var to value

  • unsetenv <var> unsets the environment variable var

  • jobs lists all the background processes spawned by the shell and their status (running or stopped) in the order they were spawned

  • kjob <job number> <signal number> sends the signal signal number to the process with the job number job number

  • fg <job number> brings the process with the job number job number to the foreground

  • bg <job number> brings the process with the job number job number to the background

  • overkill kills all the background processes spawned by the shell

  • quit exits the shell

• Signal Handling

  • Ctrl+Z stops the foreground process
  • Ctrl+C kills the foreground process

• Exit Codes in the prompt