Minishell

A fully-featured UNIX shell built from scratch in C as part of the 42 School curriculum. Features a hand-written lexer, recursive-descent parser, AST-based executor, and complete bonus support for &&, ||, * wildcards, and () subshells.

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Table of Contents

• About the Project
• Features
• Bonus Features
• Built-in Commands
• Installation
• Usage
• Usage Examples
• Architecture
• Project Structure
• Authors

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About the Project

Minishell is a minimal UNIX shell written in pure C. It faithfully reimplements the core behaviour of bash, including command execution, piping, all four I/O redirection operators, environment-variable expansion, heredocs, and a robust signal-handling strategy.

The parser constructs a full Abstract Syntax Tree (AST), enabling clean, recursive execution of arbitrarily complex command sequences — including pipelines nested inside logical operators and subshells. The project is built with strict Norminette compliance and zero memory leaks.

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Features

Core Shell Behaviour

Feature	Description
Prompt	Displays minishell$> when waiting for input
History	Full readline-backed command history (↑ / ↓ arrows)
Executables	Resolves commands via PATH, or as relative / absolute paths
Single quotes	'...' suppresses all meta-character interpretation
Double quotes	"..." suppresses everything except $ expansion
< redirect	Redirect stdin from a file
> redirect	Redirect stdout to a file (truncate)
>> redirect	Redirect stdout to a file (append)
<< heredoc	Read lines from stdin until the delimiter is matched
Pipes |	Chain command stdout → stdin across multiple processes
$ expansion	Expands environment variables inline
$?	Expands to the exit status of the last foreground pipeline
Signals	Ctrl-C re-prompts · Ctrl-D exits · Ctrl-\ is ignored

Bonus Features

Feature	Description
&& logical AND	Execute right-hand side only if left-hand side exits with 0
|| logical OR	Execute right-hand side only if left-hand side exits non-zero
* wildcard	Glob-expands a pattern against the current working directory
() subshell	Groups command sequences; runs them in a forked child process

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Built-in Commands

Command	Behaviour
echo [-n] [args…]	Print arguments; -n suppresses the trailing newline
cd [path|~]	Change working directory; updates PWD and OLDPWD
pwd	Print the absolute pathname of the current working directory
export [var=val…]	Set / update environment variables; no args prints sorted list
unset [var…]	Remove variables from the environment
env	Print all currently exported environment variables
exit [n]	Exit the shell with optional numeric status code (0–255)

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Installation

Prerequisites

• A POSIX-compliant OS (Linux / macOS)
• cc (clang or gcc)
• GNU readline development library

# Debian / Ubuntu
sudo apt-get install libreadline-dev

# macOS (Homebrew)
brew install readline

Build

git clone https://github.com/Techneera/Minishell.git
cd Minishell
make

This produces the minishell executable in the repository root.

To build with AddressSanitizer for memory debugging:

make asan

Clean

make clean   # remove object files only
make fclean  # remove object files + binary
make re      # fclean then full rebuild

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Usage

./minishell

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Usage Examples

# Basic command
minishell$> echo "Hello, World!"
Hello, World!

# Environment variable expansion
minishell$> echo $HOME
/home/user

# Exit status expansion
minishell$> ls /nonexistent; echo $?
ls: /nonexistent: No such file or directory
2

# Pipe chain
minishell$> ls -la | grep "\.c" | wc -l

# Input / output redirections
minishell$> cat < input.txt > output.txt
minishell$> echo "log entry" >> logfile.txt

# Heredoc
minishell$> cat << EOF
> line one
> line two
> EOF

# Logical AND (bonus)
minishell$> make && ./minishell

# Logical OR (bonus)
minishell$> cat missing_file || echo "file not found"

# Subshell (bonus)
minishell$> (cd /tmp && ls)

# Wildcard expansion (bonus)
minishell$> echo *.c

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Architecture

See ARCHITECTURE.md for a detailed technical breakdown of the lexer, recursive-descent parser, AST node types, execution engine, pipe model, and signal strategy.

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Project Structure

Minishell/
├── shell.c                  # Entry point: main(), REPL loop, env initialisation
├── include/
│   ├── libshell.h           # Core data structures and shared type definitions
│   ├── lexer.h              # Lexer (tokeniser) public API
│   ├── ast.h                # Recursive-descent parser and AST builder API
│   ├── expansion.h          # Variable / quote / wildcard expansion API
│   └── execution.h          # Execution engine, built-ins, and utilities API
├── src/
│   ├── lexer/               # Tokenisation: operators, words, heredoc delimiters
│   ├── ast/                 # Parser: and/or, pipeline, subshell, simple command
│   ├── execution/           # Executor: pipes, redirections, fork, built-ins, signals
│   ├── expansion/           # Word expansion: variables, quotes, wildcard masking
│   ├── builtins/            # echo, exit, exit_status, unset
│   └── wildcard/            # Glob pattern matching against the filesystem
└── libft/                   # Custom C standard-library re-implementation

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Authors

• rluis-ya — 42 Porto
• nsaraiva — 42 Porto