minishell

A POSIX-compliant Unix shell implementation written in C, as part of the 42 School curriculum.

Authors:

• Charlotte Hénique — github.com/chheniqu — charlotte.1.hq@gmail.com
• Ophélia Marbœuf — github.com/opheliamarboeuf — m.opheliaa@gmail.com

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Table of Contents

• Overview
• Features
• Architecture
• Built-in Commands
• Installation
• Usage

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Overview

Minishell recreates the core behaviour of a Unix shell — reading user input, tokenizing and parsing command lines, expanding variables, executing external programs and built-in commands, managing pipes and redirections, and handling signals interactively.

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Features

• Built using libft (custom C library)
• Interactive prompt with command history (via readline)
• Single and double quote handling with POSIX semantics
• Environment variable expansion ($VAR, $?)
• Pipes (|) with arbitrary depth
• Redirections: <, >, >>, << (heredoc)
• Signal handling (Ctrl-C, Ctrl-D, Ctrl-\, Ctrl-Z)
• Built-in commands
• Exit status propagation ($?) matching bash behaviour
• Exit status propagation ($?) matching bash behaviour
• Exit codes:
  • 0 — Success
  • 1 — General error
  • 2 — Syntax error (invalid token, unclosed quotes)
  • 126 — Command not executable (permission denied)
  • 127 — Command not found
  • 130 — Interrupted by Ctrl-C (readline or heredoc)
  • 131 — Quit by Ctrl-\
  • 128 + n — Process terminated by signal n

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Architecture

The shell processes each input line through five sequential phases:

readline input
    │
    ├─ tokenize()          → t_token linked list (with per-character quote array)
    ├─ check_quotes()      → unclosed quote validation
    ├─ has_syntax_error()  → token-level syntax validation
    ├─ expand_variable()   → $VAR / $? substitution (quote-aware)
    ├─ has_syntax_error()  → post-expansion re-check
    ├─ parser()            → t_shell_cmd + t_redir linked lists
    └─ ft_pipex()
         ├─ handle_heredoc()    → fills heredoc fds before forking
         ├─ init_pipes()        → allocates pipe fd matrix
         └─ for each command:
              ├─ [single builtin] → run in parent
              └─ [piped/compound] → fork and execute
         └─ wait_for_children() → update exit status

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Built-in Commands

Command	Behaviour
echo [-n]	Print arguments to stdout; -n suppresses the trailing newline
cd [path]	Change directory; no argument goes to $HOME; updates PWD and OLDPWD
pwd	Print the current working directory
export [KEY=VALUE]	Set/update an environment variable; no argument prints all exported variables
unset KEY	Remove an environment variable
env	Print all environment variables
exit [n]	Exit the shell with status n % 256; errors on non-numeric or too many arguments

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Installation

Dependencies: gcc, make, readline

# Clone the repository
git clone git@github.com:opheliamarboeuf/minishell.git minishell
cd minishell

# Build
make

Make target	Effect
make / make all	Build libft and link the minishell binary
make clean	Remove all object files
make fclean	Remove object files + binary + libft
make re	fclean then full rebuild

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Usage

./minishell

Launch minishell and interact with it like a regular shell:

minishell$ echo "Hello, World!"
Hello, World!

minishell$ export MY_VAR=42
minishell$ echo $MY_VAR
42

minishell$ ls -la | grep ".c" | wc -l
42

minishell$ cat << EOF
> heredoc content
> EOF

minishell$ exit