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A basic shell implementation made in C.

Installation

Requirements:

  • Linux distribution with GCC installed
  • gnome-terminal package
  • libreadline-dev package

The shell can be compiled using CMake:

$ mkdir build
$ cd build
$ cmake ..
$ make

To run the shell:

$ cd build
$ ./cshell

Features

  • Execute external programs
  • Supports program arguments
  • Inbuilt commands(eg: cd, exit, help)
  • Command history is logged and can be viewed using the up and down arrow keys
  • The shell can display colored text

The man command can be used for information regarding other programs.

Planned Features

  • Redirection: Allow redirecting the input and output of commands using the < and > operators.
  • Pipes: Allow piping the output of one command into the input of another using the | operator.
  • Job control: Allow running multiple processes in the background, and to bring them to the foreground or suspend them as needed.
  • Aliases: Allow registering command aliases.
  • Built-in arithmetic: Allow performing basic arithmetic operations directly in the shell.

Lifetime of the Shell

The shell in its lifetime has 3 basic states:

  1. Initialization: Configuration files are read and executed and the shells behavior is based on this.
  2. Execution: Commands are read from input and executed and the output is displayed in the shell.
  3. Termination: Any pending commands are executed, shell shutdown process is initiated and memory is freed.

Execution State Loop

The execution state of the shell is a loop where three basic things are done:

  • A command is read from the standard input.
  • The command string is parsed and arguments are extracted.
  • The parsed command is executed and output is displayed.

References