A Simple Shell in C

A lightweight implementation of a Unix-like shell built in C. Supports process execution, built-built in commands, and command history.

Features

• Executes external programs in separate processes.
• Supports both foreground execution (blocking until the process finishes) and background execution (non-blocking, using & at the end of the command).
• Cleans up background processes to prevent zombies.

Internal Commands

• exit: Exit the shell (rejects extra arguments).
• pwd: Display the current working directory.
• cd: Change directories, with support for:
  • No argument → go to home directory.
  • ~ expansion for home.
  • - to return to the previous directory.
• help: Display help messages for built-in commands, or identify unknown commands as external.

Signal Handling

• Gracefully handles CTRL-C (SIGINT) without terminating the shell.
• Displays help information when interrupted and re-displays the prompt.

History

• Maintains up to the 10 most recent commands with numbering.
• history: Show the last 10 commands (or fewer if less have been run).
• !!: Re-run the last command entered.
• !n: Re-run a specific command number from history.
• Ensures proper error handling for invalid history references.

Usage

Clone the repository and build with CMake:

git clone https://github.com/pnotato/shell.git
cd shell
mkdir build && cd build
cmake ..
make

Run the shell with ./shell.

The shell will display the current working directory followed by $. Enter commands as you would in a normal shell. Use & to throw a process into the background, exit to quit, and help for information on internal commands.