42sh

A fully-featured Unix shell written in C — Epitech project (TEK1)

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Table of Contents

• Overview
• Features
• Architecture
• Getting Started
  • Prerequisites
  • Build
  • Usage
• Built-in Commands
• Shell Features
• Project Structure
• Testing
• Makefile Targets

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Overview

42sh is a POSIX-inspired Unix shell implemented from scratch in C. It supports command execution, piping, redirections, environment management, history, aliases, tab-completion, and more — all without relying on readline or any external shell library.

This project was developed as part of the Epitech TEK1 shell programming module.

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Features

Category	Description
Command execution	Fork/exec with full PATH resolution
Pipelines	Multi-stage | pipelines
Redirections	>, >>, <, << (heredoc)
Logic operators	&& and || short-circuit evaluation
Command separator	; sequential execution
History	Arrow key navigation, !-event expansion, persistent ~/.42sh_history
Aliases	Define, list, remove, and auto-expand command aliases
Tab completion	Context-aware completion for commands and file paths with interactive menu
Variable expansion	$VAR, $?, $HOME, etc.
Backtick expansion	`cmd` substitution
Globbing	* wildcard expansion
Quotes	Single ' and double " quote handling
Dynamic prompt	Colored prompt showing last exit status and current directory
Raw mode	Terminal raw-mode line editor (no external library)
Signal handling	Graceful handling of SIGINT, SIGSEGV, SIGFPE

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Architecture

The shell is structured around a classic lexer → parser → AST → executor pipeline:

Input line
    │
    ▼
 Lexer            (src/parsing/lexer.c)
    │  token list
    ▼
 Parser / AST     (src/parsing/tree.c)
    │  ast_node_t tree
    ▼
 Executor         (src/execution/exec_ast.c)
    ├── Builtins  (src/execution/handle_builtins.c)
    ├── Pipes     (src/execution/exec_pipe.c)
    └── Redirs    (src/execution/exec_redir.c)

Pre-execution expansions (history events, backticks, variables, aliases, globs) are applied before the AST is executed.

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Getting Started

Prerequisites

• GCC or a compatible C compiler (epiclang alias used in the Makefile)
• make
• libncurses-dev (for terminal handling)
• libcriterion-dev (optional, for unit tests)
• gcovr (optional, for coverage)

Build

# Clone the repository
git clone <your-repo-url>
cd 42sh

# Set up git hooks (recommended)
make setup

# Build the library and binary
make

The binary 42sh will be generated in the project root.

Usage

# Interactive mode
./42sh

# Non-interactive / script mode
echo "ls -la" | ./42sh

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Built-in Commands

Command	Description
cd [path]	Change directory; supports ~, - (previous dir), and CDPATH
env	Print all exported environment variables
setenv VAR [value]	Set (or display) an environment variable
unsetenv VAR ...	Remove one or more environment variables
set	List all variables (exported and local)
unset VAR ...	Remove local shell variables
alias [name[=value]]	Define or list aliases
unalias name ...	Remove aliases
which cmd	Show the resolved path of a command
where cmd	Show all locations of a command (builtins + PATH)
repeat N cmd	Execute a command N times
exit	Exit the shell

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Shell Features

History

• Up/Down arrow keys navigate command history.
• !n — run the nth history event.
• !prefix — run the last command starting with prefix.
• !! — repeat the last command.
• History is saved to ~/.42sh_history on exit and loaded on start (up to 500 entries).

Tab Completion

Press Tab to auto-complete:

• Commands — searches PATH for matching executables and built-ins.
• Paths — completes file and directory names.
• When multiple matches exist, an interactive grid menu appears for selection.

Dynamic Prompt

[OK]~/projects/42sh $> _
[KO]~/projects/42sh $> _   # red when last command failed

• [OK] (green) or [KO] (red) reflects the exit status of the last command.
• Current directory is shown relative to $HOME using ~ notation.

Variable & Backtick Expansion

echo $HOME
echo $?
echo `whoami`

Globbing

ls *.c
cat src/**/*.c

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Project Structure

42sh/
├── main.c                    # Entry point
├── Makefile
├── include/
│   ├── my.h                  # All function prototypes
│   ├── struct_mysh.h         # All type / struct definitions
│   └── macros.h              # ANSI color macros
├── src/
│   ├── core/                 # Main shell loop (mysh.c)
│   ├── parsing/              # Lexer, AST builder, quote/inhibitor handling
│   ├── execution/            # AST executor, pipes, redirections, globbing
│   ├── builtins/             # cd, setenv, alias, which, where, repeat, set…
│   ├── environment/          # Env linked-list management, variable expansion
│   ├── history/              # History storage, navigation, event expansion
│   ├── completion/           # Tab-completion engine and menu
│   ├── alias/                # Alias tools
│   ├── termios/              # Raw-mode terminal enable/disable
│   └── bonus/                # Dynamic prompt, greeting screen
└── lib/
    └── my/                   # Custom libc reimplementations (my_strlen, etc.)

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Testing

Unit tests use the Criterion testing framework.

# Run tests + coverage summary
make tests_run

# Generate an HTML coverage report
make coverage

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Makefile Targets

Target	Description
make	Build libmy.a and 42sh binary
make clean	Remove object files
make fclean	Remove objects, binary, and library
make re	Full rebuild (fclean + all)
make tests_run	Compile and run unit tests with coverage
make coverage	Generate HTML coverage report
make setup	Configure git hooks
make help	Display help menu

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Authors

• Mathis — Epitech TEK1 — 2025/2026
• Loan — Epitech TEK1 — 2025/2026
• Matthis — Epitech TEK1 — 2025/2026
• Safwan — Epitech TEK1 — 2025/2026
• Victor — Epitech TEK1 — 2025/2026