myshell

A minimal yet feature-rich Unix-like shell implementation in C that demonstrates core operating system concepts such as process management, signal handling, terminal control, and command parsing. This project is designed with a clean, modular architecture and evolves incrementally to showcase real-world shell behaviors similar to bash.

Architecture

The shell is structured around clear, single-responsibility modules that cooperate through well-defined interfaces:

• built_in.c Handles built-in commands such as cd, pwd, exit, help, and history without forking. Built-ins execute in the parent shell context to correctly affect shell state (e.g., working directory, history).

• pid.c / pid_function.c Manages external command execution using fork() and execvp(). Returns accurate exit status to the caller, enabling correct logical operator semantics. Error handling distinguishes between fork failures and command-not-found cases.

• execute_command.c Central command dispatcher. Determines whether a command is built-in or external, routes execution accordingly, and propagates exit codes back to the main loop.

• read_input.c Implements interactive terminal input using raw mode. Supports backspace, Ctrl+C, Ctrl+D, arrow-key history navigation, and tab-based auto-completion. Ensures terminal state is safely restored after input.

• auto_complete.c Provides bash-like tab completion for commands and paths. Supports PATH-based command lookup, absolute and relative paths, nested directories, hidden files, single-match completion, and formatted multi-match listings.

• main.c The event loop of the shell. Renders the colored prompt, reads user input, parses logical operators (&&, ||), manages interactive state, installs signal handlers, and controls command chaining behavior.

Features

• Built-in commands executed without forking
• External command execution via fork() / execvp()
• Logical operators: && and ||
• Persistent command history saved in $HOME/.history
• Arrow-key navigation through command history
• Tab-based auto-completion for commands and file paths
• Nested directory and path completion
• Background process execution using &
• SIGCHLD handling for zombie process cleanup
• Robust Ctrl+C handling without terminating the shell
• Ctrl+D support to exit on empty input
• Portable runtime path handling using pathconf() (no fixed PATH_MAX)

Built-in Commands

• cd [path] – Change the current working directory (no argument defaults to $HOME)
• pwd – Print the current working directory
• history – Display command history with persistent numbering
• help – Show built-in command reference
• exit – Terminate the shell

Operator Support

• && Logical AND – Execute the right-hand command only if the left-hand command succeeds Example:

  cd /tmp && ls

• || Logical OR – Execute the right-hand command only if the left-hand command fails

Building

make

Compiles all source modules with the include path set to the include/ directory.

Running

./myshell

The shell displays a colored prompt with the current working directory and continues accepting commands until exit is invoked or Ctrl+D is pressed on an empty line.

External Commands

External programs are executed in child processes created via fork(). The parent process waits (or does not wait, for background jobs) and propagates exit codes upward. This design enables correct logical operator behavior and clean process lifecycle management.

Demo

A demo GIF showcasing interactive usage (history, auto-complete, operators) is included in the repository.

Notes

This project prioritizes clarity, correctness, and educational value over raw performance. It serves as a practical reference for understanding how real shells manage input, processes, signals, and execution flow, and is not intended for production use.