🐚 Minishell

A faithful Bash-inspired shell, built from scratch in C

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📖 About

Minishell is one of the most challenging projects at 42 — and one of the most rewarding.

The goal is simple to state: build a shell that behaves like Bash. The reality is far more complex. We had to deeply understand how a real shell works internally — how raw text input gets transformed into executable commands, how processes are spawned and connected, and how the terminal itself communicates with the OS.

Parsing was the first major challenge. Turning a raw string like echo "hello $USER" | grep -v root >> out.txt into a structured, executable command tree requires handling quotes, variable expansion, operators, and edge cases that Bash has spent decades refining. We built our own lexer and parser from scratch to handle it correctly.

Process and pipe management was the second. Every command in a pipeline runs in its own child process, connected through file descriptors. Getting fork(), pipe(), dup2() and waitpid() to work together reliably — without leaking file descriptors or creating zombie processes — required a thorough understanding of Unix process management.

Throughout the project, our reference was always Bash itself. When in doubt, we tested the behavior in Bash and matched it. The result is a shell that handles the vast majority of real-world use cases correctly.

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✨ Features

• Interactive prompt with command history
• Command execution via PATH resolution
• Pipes | — unlimited chaining of commands
• Redirections:
  • < input redirection
  • > output redirection
  • >> append to file
  • << heredoc
• Environment variable expansion — $VAR, $?
• Quote handling — single ' and double " quotes
• Signals — Ctrl+C, Ctrl+D, Ctrl+\ mirroring Bash behavior
• Built-in commands:

Command	Description
echo	Print text (-n flag supported)
cd	Change directory (relative & absolute)
pwd	Print current working directory
export	Set or update environment variables
unset	Remove environment variables
env	Display all environment variables
exit	Exit the shell with a status code

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🚀 Getting Started

Requirements

• GCC
• Make
• Unix-based OS (Linux / macOS)
• readline library

# On Ubuntu/Debian
sudo apt install libreadline-dev

Installation

git clone https://github.com/YourName/minishell.git
cd minishell
make

Usage

./minishell

minishell$ echo "Hello, $USER"
Hello, ajami

minishell$ ls -la | grep .c | wc -l
42

minishell$ cat file.txt | sort | uniq >> output.txt

minishell$ export MY_VAR=42 && echo $MY_VAR
42

minishell$ echo $?
0

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🏗️ Architecture

minishell/
├── src/
│   ├── parsing/       # Lexer, tokenizer, AST builder
│   ├── execution/     # Process management, pipes, redirections
│   ├── builtins/      # Built-in command implementations
│   ├── signals/       # Signal handling
│   └── env/           # Environment variable management
├── includes/
│   └── minishell.h
├── libft/
└── Makefile

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🧠 Key Concepts

• Lexing & Parsing — tokenizing input and building an executable command tree
• fork() / execve() — spawning child processes and executing binaries
• pipe() — inter-process communication via file descriptors
• dup2() — redirecting stdin/stdout/stderr
• waitpid() — synchronizing parent and child processes
• readline — interactive input with persistent history

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_{Made with ❤️ and a lot of segfaults at 42}