Minishell

A Unix shell implementation in C, built as part of the 42 curriculum.

Overview

This project implements a basic Unix shell with support for command execution, pipes, redirections, environment variable expansion, and built-in commands.

Custom Dependencies

Rather than relying on external libraries, I built three custom dependencies from scratch:

libft

A custom C standard library containing reimplementations of common functions:

• String manipulation (strlen, strcpy, strjoin, split, etc.)
• Memory management (memcpy, memset, calloc, etc.)
• Character classification (isalpha, isdigit, etc.)
• Linked list operations
• Custom printf implementation
• Get next line for reading input

libgc

A garbage collector library that handles automatic memory management:

• Memory allocation tracking
• Automatic cleanup on exit
• Prevents memory leaks by maintaining a collection of allocated pointers
• Custom malloc/free wrappers

libtrue

A data structures library providing:

• Generic linked list implementation
• Function pointers for flexible data handling
• Iterator and mapper functions

Core Concepts Learned

Process Management

• Fork and exec system calls
• Parent-child process relationships
• Process synchronization with wait/waitpid
• Pipe communication between processes

File Descriptors

• Standard input/output/error (0, 1, 2)
• File descriptor duplication with dup2
• Pipe file descriptors for inter-process communication
• Handling multiple redirections

Parsing and Tokenization

• Lexical analysis of command-line input
• Handling quotes (single and double)
• Environment variable expansion
• Heredoc implementation

Signal Handling

• Catching and handling SIGINT (Ctrl+C)
• SIGQUIT (Ctrl+) behavior
• Different signal behavior in parent vs child processes

Memory Management

• Tracking all allocations
• Avoiding memory leaks in complex parsing scenarios
• Building a garbage collector to simplify cleanup

Building

make

Usage

./minishell

The shell supports:

• Command execution from PATH
• Pipes (|)
• Redirections (<, >, <<, >>)
• Environment variables
• Built-ins: echo, cd, pwd, export, unset, env, exit

Built-in Commands

• echo: Print arguments to stdout (supports -n flag)
• cd: Change directory
• pwd: Print working directory
• export: Set environment variables
• unset: Unset environment variables
• env: Print environment variables
• exit: Exit the shell

Project Structure

.
├── main.c                  # Entry point and main loop
├── include/                # Header files
├── sources/                # Core functionality
│   ├── buildin/           # Built-in command implementations
│   └── utils/             # Helper functions
└── dependencies/           # Custom libraries
    ├── libft/             # Standard library reimplementation
    ├── libgc/             # Garbage collector
    └── libtrue/           # Data structures