CPP SHELL

A feature-rich, Unix-like shell implementation written in C++ with support for command execution, pipelines, history management, and tab completion.

Features

Core Shell Features

• Interactive Command Line: Full readline support with command history navigation
• Built-in Commands: exit, echo, type, pwd, cd, history
• External Command Execution: Run any executable from PATH
• Pipeline Support: Chain commands with | operator
• Tab Completion: Auto-complete commands and executables from PATH
• Quote Handling: Support for single quotes, double quotes, and escape sequences
• I/O Redirection: Basic output redirection support in echo command

Advanced Features

• Command History: Persistent command history with file support
• Path Resolution: Automatic executable discovery from PATH environment variable
• Home Directory Support: ~ expansion in cd command
• Signal Handling: Proper EOF (Ctrl+D) handling
• Error Handling: Comprehensive error messages and exit codes

Project Structure

src/
├── shell.h          # Main header file with declarations
├── main.cpp         # Main shell loop and built-in commands
├── completion.cpp   # Tab completion system
├── parser.cpp       # Command parsing and text processing
├── executor.cpp     # Command execution and pipeline handling
├── history.cpp      # History management implementation

Prerequisites

System Requirements

• Linux/Unix-like operating system
• C++17 compatible compiler (GCC 7+ or Clang 5+)
• GNU Readline library

Installing Dependencies

Ubuntu/Debian:

sudo apt-get update
sudo apt-get install build-essential libreadline-dev

Building and Running

Quick Start

# Clone or download the project
git clone <repository-url>
cd CPP-SHELL

# Build and run the code
chmod +x your_program.sh
./your_program.sh

Usage Examples

Basic Commands

$ pwd
/home/user/shell

$ echo "Hello World"
Hello World

$ type ls
ls is /bin/ls

$ cd /tmp
$ pwd
/tmp

$ cd ~
$ pwd
/home/user

Pipeline Examples

$ ls | grep .cpp
main.cpp
completion.cpp
parser.cpp

$ echo "test" | cat
test

History Management

$ history          # Show all history
$ history 5        # Show last 5 commands
$ history -w file  # Write history to file
$ history -r file  # Read history from file
$ history -a file  # Append history to file

Tab Completion

• Press Tab to auto-complete commands
• Works with both built-in commands and external executables
• Supports partial command matching

Built-in Commands

Command	Description	Usage
exit [0]	Exit the shell	exit or exit 0
pwd	Print working directory	pwd
cd [path]	Change directory	cd, cd /path, cd ~
echo [args]	Print arguments	echo Hello World
type [cmd]	Show command type/location	type ls
history [n]	Show command history	history, history 10

History Command Options

• history -w file - Write current history to file
• history -r file - Read history from file
• history -a file - Append new history entries to file

Environment Variables

The shell respects the following environment variables:

• PATH - Used for executable discovery and tab completion
• HOME - Used for ~ expansion in cd command
• HISTFILE - Persistent history file location

Configuration

Setting Up History Persistence

# In your .bashrc or .profile
export HISTFILE=~/.shell_history

# Then run the shell
./your_program.sh

Limitations

• No background job control (&, jobs, fg, bg)
• Limited I/O redirection (only basic output redirection in echo)
• No command substitution or variable expansion
• No wildcard/glob expansion
• No complex control structures (if, while, for)

Development

Code Organization

• shell.h: All function declarations and class definitions
• main.cpp: Main shell loop and built-in command implementations
• completion.cpp: Tab completion system using readline
• parser.cpp: Command parsing, tokenization, and utility functions
• pipeline.cpp: Command execution, pipeline handling, and process management
• history.cpp: History class implementation with file I/O

Adding New Built-in Commands

1. Add command name to the commands set in main.cpp
2. Add command handling logic in the main loop
3. Update tab completion in completion.cpp if needed

Future Enhancements

• Job control support
• Variable expansion and substitution
• Wildcard/glob pattern matching
• Configuration file support
• Syntax highlighting
• Command aliases

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