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🐚 Shellux - A Custom Unix Shell

Language Platform License Status

📖 Overview

Shellux (Shell + Linux) is a fully-featured custom Unix shell written in C. It provides an interactive command-line interface with support for built-in commands, process management, I/O redirection, pipes, background processes, signal handling, command history, aliases, and user-defined functions.

This shell was developed as a systems programming project to demonstrate understanding of:

  • Process creation and management (fork, exec, wait)
  • Signal handling (SIGINT, SIGTSTP, SIGCHLD)
  • File descriptors and I/O redirection
  • Inter-process communication via pipes
  • Terminal control and raw mode
  • Network programming for man page fetching

✨ Features at a Glance

Feature Description
🏠 Custom Prompt Dynamic prompt showing <username@hostname:path>
📂 hop Built-in cd command with path shortcuts
📋 reveal Built-in ls command with color coding
🔍 seek Built-in file/directory search command
📝 log Command history with persistence
🔬 proclore Process information inspector
📡 iMan Fetch man pages from the internet
👶 neonate Monitor latest PIDs in real-time
⏪ Background Processes Run commands with &
🔀 Pipes Chain commands with `
📥 I/O Redirection Support for <, >, >>
🎯 Signal Handling Ctrl+C, Ctrl+Z, Ctrl+D
📌 fg/bg Foreground/background process control
🏷️ Aliases Custom command shortcuts
🔧 Functions User-defined shell functions

🚀 Getting Started

Prerequisites

  • Operating System: Linux (tested on Ubuntu 20.04+)
  • Compiler: GCC with C11 support
  • Build Tool: Make

Installation

  1. Clone the repository

    git clone https://github.com/iDheer/MiniProject-1.git
cd MiniProject-1

  2. Build the shell

    make

  3. Run the shell

    ./bin/shellux

Alternative Build Commands

# Debug build (with symbols)
make debug

# Release build (optimized)
make release

# Clean build artifacts
make clean

# Full rebuild
make rebuild

# Install system-wide (requires sudo)
make install

# Uninstall
make uninstall

🎮 Usage

Once you start the shell, you'll see a colorful prompt:

<username@hostname:~>

The prompt shows:

  • Username: Current user
  • Hostname: System name
  • Path: Current directory (with ~ representing the shell's home directory)

Exiting the Shell

  • Type exit and press Enter
  • Press Ctrl+D (EOF signal)

📚 Built-in Commands

1. 🏠 hop - Change Directory

Navigate between directories with enhanced path handling.

Syntax:

hop [path] [path2] ...

Examples:

hop                    # Go to shell's home directory
hop ~                  # Go to shell's home directory
hop ..                 # Go to parent directory
hop .                  # Stay in current directory (prints path)
hop -                  # Go to previous directory
hop /absolute/path     # Go to absolute path
hop ~/Documents        # Go to Documents in user's home
hop dir1 dir2 dir3     # Navigate through multiple directories

Features:

  • Supports ~ for home directory
  • Supports - for previous directory (like cd -)
  • Supports . and .. for relative paths
  • Prints the new working directory after each hop
  • Can handle multiple paths in sequence

2. 📋 reveal - List Directory Contents

List files and directories with color coding and detailed information.

Syntax:

reveal [flags] [path]

Flags:

Flag Description
-a Show all files including hidden ones (starting with .)
-l Long format with permissions, size, dates, etc.

Examples:

reveal                 # List current directory
reveal -a              # Show all files including hidden
reveal -l              # Long format listing
reveal -al             # Combined: all files in long format
reveal -la             # Same as above (order doesn't matter)
reveal ~/Documents     # List specific directory
reveal -al ~           # All files in home, long format

Color Coding:

  • 🔵 Blue: Directories
  • 🟢 Green: Executable files
  • ⚪ White: Regular files

Long Format Output:

drwxr-xr-x 2 user group  4096 Dec 18 14:30 Documents
-rwxr-xr-x 1 user group 12288 Dec 18 14:25 script.sh
-rw-r--r-- 1 user group   256 Dec 18 14:20 file.txt

3. 📝 log - Command History

Manage and execute commands from history. The log persists between sessions.

Syntax:

log                     # Display command history
log purge               # Clear all history
log execute <index>     # Execute command at index

Examples:

log                     # Show last 15 commands (numbered)
log purge               # Clear the history
log execute 3           # Re-execute the 3rd most recent command

Features:

  • Stores up to 15 commands
  • Commands containing "log" are not stored (prevents recursive logging)
  • Consecutive duplicate commands are not stored
  • History is saved to command_log.txt and persists across sessions

4. 🔍 seek - Search for Files and Directories

Recursively search for files and directories matching a pattern.

Syntax:

seek [flags] <target> [directory]

Flags:

Flag Description
-d Search for directories only
-f Search for files only
-e Execute: open file/cd into directory if exactly one match

Examples:

seek file               # Search for files/dirs starting with "file"
seek -f config          # Search for files starting with "config"
seek -d src             # Search for directories starting with "src"
seek -e main.c          # Find and open main.c if single match
seek -de build          # Find and cd into 'build' dir if single match
seek config ~/project   # Search in specific directory

Output Color Coding:

  • 🔵 Blue: Directories
  • 🟢 Green: Files

Special Behavior with -e:

  • If exactly one file matches: displays its contents
  • If exactly one directory matches: changes into that directory
  • If multiple matches: only prints results

5. 🔬 proclore - Process Information

Display detailed information about a process.

Syntax:

proclore [pid]

Examples:

proclore                # Show info about the shell process
proclore 1234           # Show info about process with PID 1234

Output:

PID: 12345
Process Group: 12345
State: S (sleeping)
VmSize: 4096 kB
Executable Path: /bin/bash

State Indicators:

  • R - Running
  • S - Sleeping (interruptible)
  • T - Stopped
  • Z - Zombie
  • + suffix - Foreground process

6. 📡 iMan - Internet Man Pages

Fetch manual pages from the internet using man.he.net.

Syntax:

iMan <command_name>

Examples:

iMan ls                 # Fetch man page for 'ls'
iMan grep               # Fetch man page for 'grep'
iMan fork               # Fetch man page for 'fork' syscall

Requirements:

  • Internet connection
  • Port 80 accessible

7. 👶 neonate - PID Monitor

Continuously print the PID of the most recently created process.

Syntax:

neonate -n <time_interval>

Examples:

neonate -n 1            # Print latest PID every 1 second
neonate -n 5            # Print latest PID every 5 seconds

Controls:

  • Press x to stop the monitor and return to shell

8. 🎯 ping - Send Signals to Processes

Send signals to processes by PID.

Syntax:

ping <pid> <signal_number>

Examples:

ping 1234 9             # Send SIGKILL to process 1234
ping 1234 15            # Send SIGTERM to process 1234
ping 1234 19            # Send SIGSTOP to process 1234
ping 1234 18            # Send SIGCONT to process 1234

Note: Signal numbers are taken modulo 32.

9. 📌 fg - Bring to Foreground

Bring a background process to the foreground.

Syntax:

fg <pid>

Examples:

fg 1234                 # Bring process 1234 to foreground

10. 📌 bg - Resume in Background

Resume a stopped background process.

Syntax:

bg <pid>

Examples:

bg 1234                 # Resume process 1234 in background

11. 📊 activities - List Background Processes

Display all background processes spawned by the shell.

Syntax:

activities

Output:

[1234] : sleep 100 - Running
[5678] : vim file.txt - Stopped

States:

  • Running - Process is running
  • Stopped - Process is stopped (Ctrl+Z)
  • Terminated - Process has exited

🔀 Pipes and I/O Redirection

Input Redirection (<)

Read input from a file instead of keyboard.

sort < unsorted.txt
wc -l < file.txt

Output Redirection (>)

Write output to a file (overwrites existing content).

ls > files.txt
echo "Hello" > greeting.txt

Append Redirection (>>)

Append output to a file.

echo "New line" >> log.txt
date >> timestamps.txt

Pipes (|)

Connect the output of one command to the input of another.

ls | wc -l                      # Count files
cat file.txt | grep pattern     # Search in file
ps aux | grep firefox | head    # Complex pipeline

Combined Example

cat input.txt | sort | uniq > output.txt
grep error < log.txt | wc -l >> count.txt

⏪ Background Processes

Run commands in the background by appending &.

sleep 100 &                     # Run sleep in background
gedit file.txt &                # Open editor in background
./long_script.sh &              # Run script in background

Features:

  • Background processes print their PID when started
  • Use activities to list all background processes
  • Use fg <pid> to bring to foreground
  • Use bg <pid> to resume stopped process
  • Shell notifies when background processes exit

🎯 Signal Handling

Keyboard Signals

Signal Key Behavior
SIGINT Ctrl+C Terminates foreground process (not the shell)
SIGTSTP Ctrl+Z Stops foreground process, moves to background
EOF Ctrl+D Exits shell (after killing all background processes)

Signal Behavior

  • Foreground process running: Signal affects only the foreground process
  • No foreground process: Signal is ignored with a message
  • Shell protection: The shell itself ignores Ctrl+C and Ctrl+Z

🏷️ Aliases and Functions

Configuration File

The shell reads shellux.myshrc on startup to load aliases and functions.

Alias Format

alias shortname=command

Example shellux.myshrc:

alias dikhao=ls
alias cls=clear
alias ll=ls -la

Usage:

dikhao                  # Executes 'ls'
cls                     # Executes 'clear'

Function Format

function_name()
{
    command1 "$1"
    command2
}

Example Functions:

mk_hop()
{
    mkdir "$1"
    hop "$1"
}

hop_seek()
{
    hop "$1"
    seek "$1"
}

Usage:

mk_hop new_project      # Creates 'new_project' and cd's into it
hop_seek Documents      # cd to Documents and search there

Note: $1 is replaced with the first argument passed to the function.

🔄 Multiple Commands

Execute multiple commands in sequence using ;.

hop ~ ; reveal ; proclore
mkdir test ; hop test ; reveal

Commands are executed left to right, regardless of previous command's exit status.

🎨 Prompt Customization

The prompt is dynamically generated with colors:

<username@hostname:path>
Component Color
<, > Teal (bold)
username@hostname Teal (bold)
: Default
path Coral (bold)

Path Display:

  • ~ when in shell's home directory
  • ~/subdir when in subdirectory of home
  • Full path for directories outside home

📁 Project Structure

MiniProject-1/
├── main.c              # Entry point, signal handlers, main loop
├── commands.c          # Built-in commands implementation
├── commands.h          # Command function declarations
├── utils.c             # Utility functions, command execution
├── utils.h             # Utility function declarations
├── globals.c           # Global variables, helper functions
├── globals.h           # Global declarations, structs, macros
├── prompt.c            # Prompt display logic
├── prompt.h            # Prompt function declarations
├── alias.c             # Alias and function handling
├── alias.h             # Alias declarations
├── shellux.myshrc      # Configuration file (aliases/functions)
├── Makefile            # Build configuration
├── test_shell.sh       # Testing script
├── README.md           # This documentation
├── bin/                # Compiled binary
│   └── shellux
└── obj/                # Object files
    └── *.o

🔧 Technical Details

Memory Management

  • Dynamic allocation for background process tracking
  • Proper cleanup on shell exit
  • Memory is freed for command history and process lists

Process Management

  • Foreground processes are waited on with waitpid
  • Background processes use non-blocking waitpid with WNOHANG
  • SIGCHLD handler cleans up terminated background processes

Signal Safety

  • Critical sections use signal blocking
  • Foreground PID updates are protected
  • Async-signal-safe functions used in handlers

File Descriptors

  • Proper dup2 usage for redirection
  • File descriptors closed after duplication
  • Multiple pipe support with dynamic fd allocation

🧪 Testing

Run the comprehensive test suite:

# Make test script executable
chmod +x test_shell.sh

# Run all tests
./test_shell.sh

# Run quick tests only
./test_shell.sh --quick

# Show help
./test_shell.sh --help

Manual Testing

# Start the shell
./bin/shellux

# Try these commands:
hop ~
reveal -al
echo "Hello World" > test.txt
cat test.txt
ls | grep test | wc -l
sleep 10 &
activities
proclore
log
exit

🐛 Known Limitations

  1. Platform: Linux only (uses /proc filesystem)
  2. Tab Completion: Not implemented
  3. Arrow Keys: History navigation via arrows not supported
  4. Job Control: Limited to basic fg/bg operations
  5. Quoted Strings: Limited support for complex quoting
  6. Environment Variables: $VAR expansion not implemented
  7. Wildcards: Glob patterns (*, ?) not expanded

🤝 Contributing

Contributions are welcome! Please:

  1. Fork the repository
  2. Create a feature branch (git checkout -b feature/amazing-feature)
  3. Commit changes (git commit -m 'Add amazing feature')
  4. Push to branch (git push origin feature/amazing-feature)
  5. Open a Pull Request

📜 License

This project is licensed under the MIT License - see the LICENSE file for details.

👤 Author

Inesh Dheer

🙏 Acknowledgments

  • Operating Systems course concepts
  • Linux man pages
  • GNU Bash for inspiration
  • man.he.net for online man pages

📊 Command Reference Quick Card

Command Description Example
hop Change directory hop ~/Documents
reveal List files reveal -al
seek Search files seek -f config
log Command history log execute 3
proclore Process info proclore 1234
iMan Online man iMan grep
neonate PID monitor neonate -n 2
ping Send signal ping 1234 9
fg Foreground fg 1234
bg Background bg 1234
activities List bg procs activities
exit Exit shell exit

Made with ❤️ by Inesh Dheer

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Shellux - A custom Unix shell in C with pipes, I/O redirection, job control, signals, and 12+ built-in commands

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