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

• https://www.geeksforgeeks.org/making-linux-shell-c/
• https://brennan.io/2015/01/16/write-a-shell-in-c/