Simple Shell

A lightweight Unix shell implementation in C that provides essential command-line functionality including built-in commands, program execution, environment variable management, and alias support.

Features

• Built-in Commands

  • cd [dir] - Change the working directory
  • exit [STATUS] - Exit the shell with optional status code
  • env - Display environment variables
  • setenv VARIABLE VALUE - Set or modify an environment variable
  • unsetenv VARIABLE - Remove an environment variable
  • help [BUILTIN_NAME] - Display help information
  • alias [name='value'] - Create, display, or modify aliases

• External Program Execution

  • Forks child processes to execute external commands
  • Searches PATH for executables
  • Properly handles exit codes and signals

• Additional Features

  • Interactive mode with prompt (dali<3 )
  • Non-interactive mode for reading commands from files
  • Signal handling (Ctrl+C)
  • Variable expansion ($VAR)
  • Alias expansion
  • Error reporting and status codes

Building

Compile the shell with gcc:

gcc -o simple_shell *.c

Usage

Interactive Mode

Run the shell and start typing commands:

./simple_shell
dali<3 ls -l
dali<3 cd /home
dali<3 exit

Non-Interactive Mode

Execute commands from a file:

./simple_shell commands.txt

Examples

# Change directory
dali<3 cd /tmp

# List files (external command)
dali<3 ls -la

# Set environment variable
dali<3 setenv MYVAR "hello world"

# Display environment
dali<3 env

# Create an alias
dali<3 alias ll="ls -la"

# Use the alias
dali<3 ll

# Get help
dali<3 help cd
dali<3 help

# Exit with status
dali<3 exit 0

Project Structure

• main.c - Entry point and main loop
• exec.c - Command execution using fork/execve
• builtin.c - Built-in commands (env, setenv, unsetenv, exit, alias)
• more_builtin.c - Additional built-in commands (cd, help)
• env_manage.c - Environment variable management
• alias_manage.c - Alias management
• tokensize.c - Input tokenization
• strtok.c - String tokenization
• _getline.c - Input line reading
• helpers.c - String utility functions
• more_helpers.c - Additional helper functions
• even_more_helpers.c - More helper functions
• fin_paths.c - Path resolution
• exp.c - Variable and alias expansion
• shell.h - Header file with structures and function declarations
• macro.h - Macros for messages and configuration

Implementation Details

• Uses fork() and execve() for process creation
• Maintains its own copy of the environment variables
• Uses a custom data structure (data_of_program) to track program state
• Handles signals gracefully (Ctrl+C displays a new prompt)
• Supports chaining commands via logic operators
• Implements custom string functions to avoid libc dependencies where possible

License

This project is provided as-is for educational purposes.