This project has been created as part of the 42 curriculum by surayama, kjikuhar.

minishell

Description

Minishell is a simplified shell implementation written in C, inspired by bash. The goal of this project is to understand how a real shell works by building one from scratch: parsing user input, managing environment variables, handling redirections and pipes, and executing commands.

Key features include:

• Interactive prompt with command history (GNU readline)
• Tokenization and parsing of shell commands into an AST (Abstract Syntax Tree)
• Pipes (|) and redirections (<, >, >>, <<)
• Environment variable expansion ($VAR, $?)
• Quote handling (single and double quotes)
• Here-documents (<<)
• Built-in commands: echo, cd, pwd, export, unset, env, exit
• Signal handling (Ctrl+C, Ctrl+D, Ctrl+\)

Instructions

Prerequisites

• GCC, Make, GNU readline library

Build and Run

# Build the project
make

# Run the shell
./minishell

Other Make Targets

Command	Description
make	Build the project
make re	Clean rebuild
make clean	Remove object files
make fclean	Remove object files and binary

Usage Examples

$ ./minishell
minishell$ echo hello world
hello world
minishell$ ls -la | grep Makefile
-rw-r--r--  1 user  staff  2048 Apr 10 12:00 Makefile
minishell$ export FOO=bar
minishell$ echo $FOO
bar
minishell$ cat << EOF
> hello
> world
> EOF
hello
world
minishell$ exit

Architecture

The shell follows an interpreter pipeline:

Input -> tokenize() -> heredoc() -> parse() -> AST -> expand() -> execute

1. Tokenizer -- State-machine-based lexer that splits input into tokens at operator, space, and quote boundaries.
2. Heredoc -- Processes here-document redirections before parsing.
3. Parser -- Recursive descent parser that produces a binary AST with PIPE, AND, OR, SUBSHELL (internal) and CMD (leaf) nodes.
4. Expand & Execute -- Walks the AST and, for each command, applies expansion (tilde, $?, parameter, wildcard, quote removal) then executes via fork/execve.

Resources

• The Open Group Base Specifications -- Shell Command Language
• Bash Reference Manual
• Writing Your Own Shell (42 tutorial)
• GNU Readline Library Documentation

Use of AI

AI (Claude Code by Anthropic) was used as a development assistant for the following tasks:

• Code review and debugging assistance
• Generating boilerplate code and Makefile configurations