🐚 Minishell — Custom Linux Shell in C

A minimal Linux shell written in C that reads commands from a prompt, executes them using system calls, supports pipes, handles signals, and manages background jobs — just like a real terminal.

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🔍 How It Works

User types a command
        ↓
  get_command()        ← extract command name
        ↓
check_command_type()   ← BUILTIN / EXTERNAL / NO_COMMAND
        ↓              ↓
execute_internal()   fork() + execvp()

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✨ Features

• 💬 Custom prompt — change anytime with PS1=newprompt
• 🔧 Built-in commands — cd, pwd, echo, exit, jobs, fg, bg
• ⚡ External commands — 150+ Linux commands via fork() + execvp()
• 🔗 Pipes — chain commands using |
• 📡 Signal handling — Ctrl+C and Ctrl+Z handled gracefully
• 🌙 Job control — suspend, list, and resume background processes

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🗂️ Project Structure

Minishell/
├── main.c          # Entry point — initializes prompt and starts the shell
├── scan_input.c    # Shell loop — reads input, routes commands, handles signals
├── commands.c      # Executes built-in and external commands, handles pipes
├── header.h        # Structs, macros, and all function declarations
└── ext_cmds.txt    # List of supported external commands (loaded at startup)

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🚀 Build & Run

Prerequisites

• GCC compiler
• Linux / Unix environment

Compile

gcc main.c scan_input.c commands.c -o minishell

Run

./minishell

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📖 Usage

Basic commands

minishell$: pwd
/home/amar

minishell$: cd /tmp

minishell$: ls | grep .c
main.c
scan_input.c
commands.c

Built-in commands

minishell$: echo $$        # shell PID
minishell$: echo $?        # last exit status
minishell$: echo $SHELL    # shell path

Job control

minishell$: sleep 100      # press Ctrl+Z to suspend
minishell$: jobs
[1] Stopped  sleep 100
minishell$: fg             # resume in foreground
minishell$: bg             # resume in background

Custom prompt

minishell$: PS1=dev>
dev>

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⚙️ Signal Handling

Signal	Shortcut	What happens
SIGINT	Ctrl+C	Cancels current command, re-shows prompt
SIGTSTP	Ctrl+Z	Suspends process, adds it to jobs list
SIGCHLD	auto	Cleans up finished background processes

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🧠 Key Concepts Used

Concept	Purpose
fork() + execvp()	Run external commands in a child process
pipe() + dup2()	Connect stdout of one command to stdin of the next
waitpid()	Wait for child; detect stopped jobs
signal() + kill()	Handle Ctrl+C, Ctrl+Z and resume jobs
getcwd() + chdir()	Implement pwd and cd
File I/O (open, read)	Load ext_cmds.txt at startup

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👤 Author

Amar C M — Embedded Systems Engineer

· [email protected]

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📜 License

MIT License — free to use and modify with attribution.