This project has been created as part of the 42 curriculum by caide-so, marcudos.

Minishell

As beautiful as a shell

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Description

Minishell is a simplified Unix shell implementation built as part of the 42 School curriculum. The goal is to recreate the core behavior of bash, gaining hands-on understanding of how shells work under the hood — from parsing user input to managing processes, file descriptors, and signals.

This project covers the entire pipeline of a shell:

• Tokenization — breaking raw input into meaningful tokens
• Syntax analysis — validating token structure before execution
• AST (Abstract Syntax Tree) construction — representing command logic as a tree
• Expansion — handling environment variables, $?, wildcards, and quote rules
• Execution — running builtins, external commands, pipes, redirections, and subshells
• Signal handling — responding correctly to Ctrl-C, Ctrl-D, and Ctrl-\

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Features

Mandatory

• Interactive prompt with command history
• Executable lookup via PATH, relative, and absolute paths
• Single and double quote handling
• Environment variable expansion ($VAR, $?)
• Redirections: <, >, >>, << (heredoc)
• Pipes (|) connecting command outputs to inputs
• Signal handling: Ctrl-C, Ctrl-D, Ctrl-\
• Built-in commands:
  • echo (with -n)
  • cd (relative and absolute paths)
  • pwd
  • export
  • unset
  • env
  • exit

Bonus

• Logical operators && and || with parenthesis-based priority
• Wildcard * expansion in the current working directory

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Instructions

Requirements

• GCC compiler
• GNU Make
• readline library (libreadline-dev on Debian/Ubuntu)

Compilation

# Clone the repository
git clone  minishell
cd minishell

# Build the project
make

# Build with bonus features
make bonus

Running

./minishell

Cleanup

# Remove object files
make clean

# Remove object files and binary
make fclean

# Full recompile
make re

Memory Check (optional)

A readline.supp valgrind suppression file is included to filter readline's known leaks:

make leak

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Project Structure

minishell/
├── include/
│   ├── minishell.h       # Main header with all function prototypes
│   ├── structs.h         # All struct and enum definitions
│   └── colors.h          # ANSI color macros for the prompt
├── src/
│   ├── main.c            # Entry point, prompt loop, parser
│   ├── tokenizer/        # Input → token list
│   ├── syntax/           # Token validation
│   ├── ast/              # Token list → AST
│   ├── expansion/        # Variable, wildcard, and quote expansion
│   ├── executor/         # AST execution, pipes, redirections
│   ├── builtin/          # Built-in command implementations
│   ├── heredoc/          # Heredoc input processing
│   ├── signal/           # Signal handler setup
│   ├── env/              # Environment variable management
│   ├── prompt/           # Prompt string construction
│   └── clean/            # Memory cleanup utilities
├── libft/                # Personal C utility library
└── Makefile

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Resources

Official Documentation

• Bash Reference Manual — the primary reference for expected behavior
• GNU Readline Library — documentation for readline, add_history, and related functions
• POSIX Shell Specification — formal shell grammar and behavior

Articles & Tutorials

• Writing a Unix Shell (Part I, II, III) — Indradhanush Gupta — excellent walkthrough of shell internals
• Building a Shell in C — Stephen Brennan — concise practical guide
• Abstract Syntax Trees — Wikipedia — background on AST concepts
• Linux man pages — for all syscalls used: fork, execve, pipe, dup2, waitpid, sigaction, etc.

42-Specific References

• 42 Norm — coding style enforced on all source files
• Valgrind Documentation — used for memory leak detection during development

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AI Usage

AI tools (primarily Claude) were used during this project in the following ways:

• Debugging assistance — describing unexpected behaviors and getting suggestions on where to investigate (e.g., signal handling edge cases, heredoc fd management)
• Documentation drafting — generating initial function comment blocks, which were then reviewed, corrected, and adapted to match actual implementation
• Prompt refinement — asking targeted questions about specific POSIX/bash behaviors (e.g., how $? expands inside heredocs, expected exit codes for signals)
• README structure — this file was drafted with AI assistance and reviewed to ensure accuracy

In all cases, AI-generated content was critically reviewed before use. No logic or implementation was copied from AI output without full understanding — all core algorithms (tokenizer, parser, AST, expander, executor) were written and reasoned through by the authors.

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Authors

• caide-so — caide-so@student.42sp.org.br
• marcudos — marcudos@student.42sp.org.br