A simple shell implementation in C

This is a simple shell implementation in C, designed to provide a command-line interface with various features and built-in commands.

Features

• Command Execution: Execute standard Unix commands.
• Pipelines: Support for command pipelines (e.g., ls | grep txt).
• Redirection: Input and output redirection (e.g., ls > output.txt).
• Command History: Maintain a history of executed commands.
• Environment Variables: Use environment variables (e.g., echo $PATH).
• Backend Commands: Execute backend commands.
• Prompt Execution Time: Displays the execution time of the last command in the prompt.
• Save/Load History: Automatically saves command history to .ps_history file and loads it when the shell starts.
• Welcome Message and Help Command: Displays a welcome message when the shell starts and includes a help command to show available commands and usage information.
• Colorful Prompt: Customizable colorful prompt for better visual distinction.
• Wildcard Expansion: Support for * and ? wildcards in file name expansion.

Built-in Commands

• cd: Change the current directory
• pwd: Print the current working directory
• history: Display or manipulate the command history
• jobs: List active jobs
• exit: Exit the shell
• help: Display help information about built-in commands