🐚 minishell

As beautiful as a shell — a custom Unix shell built from scratch in C, recreating the core behavior of bash.

---

📖 About

minishell is a project from 42 School that challenges you to implement a functional Unix shell from scratch. It deepens understanding of processes, file descriptors, signals, and how a shell actually works under the hood.

The shell supports interactive use with a prompt, command history, pipes, redirections, environment variable expansion, and a set of built-in commands — closely mimicking the behavior of bash.

---

✨ Features

Core Shell Behavior

• Interactive prompt — displays a prompt and waits for user input
• Command history — navigate previous commands with arrow keys (via readline)
• Executable lookup — resolves commands using PATH, relative, or absolute paths

Quoting & Parsing

Token	Behavior
'single quotes'	Prevents all interpretation of meta-characters
"double quotes"	Prevents all interpretation except $ (dollar sign)

Redirections

Operator	Description
<	Redirect stdin from a file
>	Redirect stdout to a file (overwrite)
>>	Redirect stdout to a file (append)
<<	Here-doc: read input until a delimiter line is seen

Pipes

• cmd1 \| cmd2 \| cmd3 — chains commands, connecting stdout of each to stdin of the next

Environment Variables

• $VAR expands to the value of VAR
• $? expands to the exit status of the last foreground pipeline

Signal Handling

Signal	Interactive behavior
Ctrl-C	Displays a new prompt on a new line
Ctrl-D	Exits the shell
Ctrl-\	Does nothing

⚠️ A single global variable is used exclusively to store the received signal number — no structs or additional data in global scope.

---

🔧 Built-in Commands

Command	Description
echo [-n]	Print text; -n suppresses trailing newline
cd [path]	Change directory (relative or absolute path)
pwd	Print current working directory
export [var=value]	Set or export environment variables
unset [var]	Remove environment variables
env	Print all environment variables
exit	Exit the shell

---

🚀 Getting Started

Requirements

• GCC or Clang
• GNU Make
• readline and history libraries — install with your package manager:

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

# macOS (Homebrew)
brew install readline

Build

git clone https://github.com/yourusername/minishell.git
cd minishell
make

Run

./minishell

Makefile Targets

make        # Build the binary
make clean  # Remove object files
make fclean # Remove object files and binary
make re     # fclean + build

---

🔍 Implementation Notes

• Parsing is done in multiple passes: lexing (tokenizing the raw input), then parsing (building a command table / AST) with proper handling of quotes and expansions.
• Execution forks child processes for external commands; built-ins run in the current process (or in a subshell when part of a pipeline).
• Pipes are implemented with pipe(), fork(), and dup2() to wire file descriptors between commands.
• Here-doc (<<) reads from a temporary pipe until the delimiter is matched, without updating history.
• Memory: All heap allocations are tracked and freed. Note that readline() itself may produce leaks, but those are out of scope per the project spec.

---

📚 Allowed External Functions

readline, rl_clear_history, rl_on_new_line, rl_replace_line, rl_redisplay, add_history, printf, malloc, free, write, access, open, read, close, fork, wait, waitpid, signal, sigaction, sigemptyset, sigaddset, kill, exit, getcwd, chdir, stat, lstat, fstat, unlink, execve, dup, dup2, pipe, opendir, readdir, closedir, strerror, perror, isatty, ttyname, ttyslot, ioctl, getenv, tcsetattr, tcgetattr, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs

---

📝 License

This project is part of the 42 School curriculum. Feel free to use it as a reference, but please don't submit it as your own work.

---

Tested against bash behavior. When in doubt, bash is the reference.