minish

A tiny Unix shell written in C as a side project.

The goal is to build a shell from scratch and learn how processes, file descriptors, input handling, pipes, redirection, and system calls work.

To Build

make ./minish

To Run

./minish

Features

Phase 1 - Input Loop

• Interactive and non-interactive modes
• Command-line input using getline()
• isatty() detection
• exit and EOF handling

Phase 2 - External Commands

• Execute external programs
• Command arguments
• Process creation with fork()
• Program execution with execvp()
• Parent synchronization with waitpid()

Examples:

minish$ ls
minish$ ls -la
minish$ echo hello
minish$ pwd

Phase 3 - Built-ins

• cd — change working directory
• env — display environment variables
• exit — exit the shell

Built-ins are handled directly by Minish rather than executed as separate processes.

Phase 4 - I/O Redirection

• < — redirect standard input
• > — redirect standard output
• >> — append standard output
• File handling with open()
• File descriptor replacement with dup2()

Examples:

minish$ cat < file.txt
minish$ echo hello > file.txt
minish$ echo world >> file.txt

Phase 5 - Pipes

• Unix pipes using pipe()
• Multiple commands connected with |
• Process communication through file descriptors
• Pipeline synchronization with waitpid()

Example:

minish$ ls | grep .c
minish$ ls | wc -l

Phase 6 - Signals

• SIGINT handling for Ctrl-C
• SIGQUIT handling
• Separate signal behavior for the shell and child processes
• Signal configuration using sigaction()

Phase 7 - Command Parsing

• Dedicated command parser
• Separation of parsing and execution
• Quoted arguments
• Environment variable expansion
• Unmatched quote detection

Examples:

minish$ echo "hello world"
minish$ echo 'hello world'
minish$ echo $HOME
minish$ echo $USER

Project Structure

minish/
├── include/
│   └── minish.h
├── src/
│   ├── main.c
│   ├── input.c
│   ├── executor.c
│   ├── builtins.c
│   ├── pipes.c
│   ├── signals.c
│   └── parser.c
├── Makefile
├── .gitignore
├── LICENSE
└── README.md

Build

make

To perform a clean rebuild: make re

Run

./minish

Clean

make clean

Remove all build files and the executable: make fclean

Current Limitations

Minish is intentionally developed incrementally. Advanced shell features such as:

• More complete quoting rules
• Complex command parsing
• Advanced redirection
• Command history
• Job control
• Shell scripting features
• Wildcard expansion

are not yet implemented.

License

MIT License