Simple Shell - HSH

A simple UNIX command line interpreter (shell) built in C language as part of the ALX SE Program.

📋 Table of Contents

• Features
• Installation
• Usage
• Built-in Commands
• External Commands
• Advanced Features
• Examples
• Project Structure
• Authors

✨ Features

Core Shell Functionality

• Interactive and Non-interactive modes
• Command execution with arguments
• PATH environment variable resolution
• Built-in command support
• Signal handling (Ctrl+C)
• Error handling with proper exit codes
• Memory management and cleanup

Enhanced User Experience

• Current working directory display in prompt
• Smart directory navigation
• Environment variable support
• Command history tracking

🔧 Installation

Prerequisites

• GCC compiler
• Linux/Unix environment
• Standard C library

Compilation

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh

Run the Shell

./hsh

🚀 Usage

Interactive Mode

Launch the shell and interact with it directly:

$ ./hsh
/home/user/simple_shell$ ls -la
/home/user/simple_shell$ cd /tmp
/tmp$ pwd
/tmp$ exit

Non-Interactive Mode

Execute commands via pipes or input redirection:

$ echo "ls -la" | ./hsh
$ echo -e "pwd\ncd ..\npwd" | ./hsh

🔨 Built-in Commands

cd - Change Directory

Navigate between directories with full support for:

• cd - Go to HOME directory
• cd [directory] - Change to specified directory
• cd .. - Go to parent directory
• cd - - Return to previous directory

Examples:

/home/user$ cd /tmp
/tmp$ cd ..
/$ cd -
/tmp$ cd
/home/user$

env - Environment Variables

Display all environment variables:

/home/user$ env
PWD=/home/user
PATH=/usr/local/bin:/usr/bin:/bin
HOME=/home/user
USER=user
...

exit - Exit Shell

Exit the shell with optional status code:

/home/user$ exit
$ echo $?
0

🔧 External Commands

The shell supports all standard UNIX commands available in your PATH:

File and Directory Operations

• ls - List directory contents
• pwd - Print working directory
• mkdir - Create directories
• rmdir - Remove directories
• cp - Copy files
• mv - Move/rename files
• rm - Remove files
• find - Search files and directories

Text Processing

• echo - Display text
• cat - Display file contents
• grep - Search text patterns
• sort - Sort lines
• uniq - Remove duplicates
• wc - Count words, lines, characters

System Information

• ps - Process information
• who - Show logged users
• date - Display date and time
• uname - System information

Examples:

/home/user$ ls -la
/home/user$ echo "Hello, World!"
/home/user$ cat file.txt
/home/user$ ps aux
/home/user$ which ls

🎯 Advanced Features

Smart Prompt Display

• Current directory shown in prompt
• **Home directory abbreviated as ~**
• Subdirectories shown relative to home

/home/user/simple_shell$ cd Documents
/home/user/Documents$ cd ..
/home/user$ cd /
/$ cd home/user
/home/user$

PATH Resolution

Automatically finds executables in PATH directories:

$ /bin/ls        # Absolute path
$ ls             # Found via PATH resolution

Environment Variable Handling

• PWD - Always updated with current directory
• OLDPWD - Tracks previous directory for cd -
• PATH - Used for command resolution
• HOME - Used for cd with no arguments

Signal Handling

• Ctrl+C (SIGINT) - Gracefully handled, returns to prompt
• Clean exit - Proper memory cleanup on exit

Error Handling

• Command not found - Clear error messages
• Permission denied - Proper error reporting
• Invalid directory - Helpful error messages

$ invalidcommand
./hsh: 1: invalidcommand: not found
$ cd /invalid/path
./hsh: 1: cd: can't cd to /invalid/path

📝 Examples

Basic Usage

$ ./hsh
/home/user/simple_shell$ pwd
/home/user/simple_shell
/home/user/simple_shell$ ls -la
total 156
drwxr-xr-x 3 user user  4096 Dec  6 14:37 .
drwxr-x--- 5 user user  4096 Dec  6 14:39 ..
-rwxr-xr-x 1 user user 26624 Dec  6 14:37 hsh
...

Directory Navigation

/home/user/simple_shell$ cd /tmp
/tmp$ pwd
/tmp
/tmp$ cd -
/home/user/simple_shell$ cd ..
/home/user$ cd simple_shell
/home/user/simple_shell$

Environment Variables

/home/user$ env | grep PATH
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
/home/user$ echo $HOME
$HOME

Command Execution

/home/user$ echo "Hello World"
Hello World
/home/user$ which ls
/usr/bin/ls
/home/user$ date
Fri Dec  6 14:37:22 UTC 2024

📁 Project Structure

simple_shell/
├── main.h              # Header file with function prototypes
├── main.c              # Main shell loop and initialization
├── prompt.c            # Prompt display and directory handling
├── _fork.c             # Process creation and execution
├── _func1.c            # String manipulation functions
├── _func2.c            # Input handling functions
├── _func3.c            # Token parsing functions
├── _func4.c            # Built-in commands implementation
├── path.c              # PATH resolution functions
├── _env.c              # Environment variable functions
├── _env_non.c          # Non-interactive environment handling
├── non_interactive.c   # Non-interactive mode implementation
├── name_of_prg.c       # Program name handling
├── AUTHORS             # Project authors
└── README.md           # This file

🔍 Technical Details

Memory Management

• Dynamic memory allocation for command buffers
• Proper cleanup on exit and error conditions
• No memory leaks in normal operation

Process Handling

• Fork-exec model for external commands
• Proper parent-child process synchronization
• Signal handling for interrupts

String Processing

• Custom string manipulation functions
• Safe buffer handling
• Tokenization and parsing

🚫 Limitations

• No pipe (|) support
• No redirection (>, <, >>) support
• No command substitution
• No variable assignment
• No scripting support (if/while/for)
• No job control (background processes)

🤝 Authors

See the AUTHORS file for contributor information.