Minishell

A minimal shell implementation in C, created as part of the 42 curriculum. This project implements a simplified version of a Unix shell with support for command execution, pipelines, redirections, and built-in commands.

Features

Built-in Commands

• cd - Change directory
• pwd - Print working directory
• echo - Print arguments
• env - Display environment variables
• export - Set environment variables
• unset - Unset environment variables
• exit - Exit the shell

Advanced Features

• Pipelines - Chain commands using | operator
• Redirections:
  • Input redirection: <
  • Output redirection: >
  • Append redirection: >>
  • Heredoc: <<
• Environment Variable Expansion - Support for $VAR and ${VAR} syntax
• Command History - Built-in history support using readline
• Signal Handling - Proper handling of SIGINT (Ctrl+C) and SIGQUIT
• External Commands - Execute system commands from PATH

Requirements

• gcc or cc compiler
• make
• readline library (development headers)

Installing readline (Ubuntu/Debian)

sudo apt-get install libreadline-dev

Installing readline (macOS)

brew install readline

Building

To compile the project, simply run:

make

This will create the minishell executable.

Clean Build Artifacts

make clean      # Remove object files
make fclean     # Remove object files and executable
make re         # Clean and rebuild

Usage

Run the shell:

./minishell

You'll see the prompt minishell$ where you can enter commands.

Examples

# Basic commands
minishell$ pwd
minishell$ ls -la
minishell$ echo "Hello, World!"

# Environment variables
minishell$ export MY_VAR="test"
minishell$ echo $MY_VAR

# Pipelines
minishell$ ls | grep .c
minishell$ cat file.txt | wc -l

# Redirections
minishell$ ls > output.txt
minishell$ cat < input.txt
minishell$ echo "text" >> file.txt

# Heredoc
minishell$ cat << EOF
> line 1
> line 2
> EOF

# Change directory
minishell$ cd /path/to/directory
minishell$ cd ~

# History
minishell$ history          # Show command history
minishell$ history -c       # Clear history

Exiting

Type exit or press Ctrl+D to exit the shell.

Project Structure

miniShell-2/
├── main.c                 # Main entry point and execution logic
├── minishell.h            # Header file with all declarations
├── Makefile               # Build configuration
├── exec/                  # Built-in command implementations
│   ├── builtins_cd.c
│   ├── builtins_pwd.c
│   ├── builtins_echo.c
│   ├── builtins_env.c
│   ├── builtins_exit.c
│   ├── builtins_export.c
│   └── builtins_unset.c
├── parsing/               # Parsing and tokenization
│   ├── tokenization.c     # Tokenize input string
│   ├── parsing.c          # Parse tokens into AST
│   ├── parse_cmd.c        # Parse individual commands
│   ├── split.c            # String splitting utilities
│   ├── copy_env.c         # Environment variable management
│   └── free_args.c        # Memory cleanup
└── utils/                 # Utility functions
    ├── utils1.c
    ├── utils2.c
    ├── export.c           # Export functionality
    ├── unset.c            # Unset functionality
    ├── heredoc.c          # Heredoc implementation
    └── helper.c           # Helper functions

Implementation Details

Architecture

The shell follows a typical shell architecture:

1. Read Line - Uses readline library to get user input
2. Tokenization - Breaks input into tokens (commands, arguments, operators)
3. Parsing - Builds an Abstract Syntax Tree (AST) from tokens
4. Execution - Traverses AST and executes commands:
   • Built-in commands execute directly
   • External commands fork and exec
   • Pipelines create pipes between processes
   • Redirections modify file descriptors

Data Structures

• AST (Abstract Syntax Tree) - Represents the command structure
• Token - Represents a tokenized element (command, argument, operator)
• Command - Contains command name, arguments, and redirections
• Environment List - Linked list of environment variables

Limitations

This is a minimal shell implementation and may not support all features of a full shell like bash:

• No support for logical operators (&&, ||)
• No support for command substitution
• Limited error handling in some edge cases
• No job control (background processes, &)

Authors

• abdelilah
• yolaidi-

License

This project is part of the 42 curriculum and follows the 42 coding standards.