MyShell - A Feature-Rich Unix Shell

MyShell is a custom Unix-like command-line interpreter (shell) written in C. It supports standard command execution, command history, piping, input/output redirection, and includes advanced features like Tab Completion and a built-in Arithmetic Evaluator.

🌟 Features

MyShell is designed to be a powerful and user-friendly alternative shell, incorporating features typically found in modern shells:

Core Shell Functionality

• Command Execution: Executes external programs and system commands.
• Piping (|): Supports connecting the output of one command to the input of another.
• Input/Output Redirection (<, >): Allows redirecting command input from a file or output to a file.

Advanced Interaction

• Tab Completion: Provides auto-completion for both external commands (by searching the $PATH) and local files/directories.
  • Pressing TAB once will complete a single match or, if multiple matches exist, pressing TAB again will list all possibilities.
• Command History: Stores and manages command history, allowing easy navigation2].
  • Use the UP and DOWN arrow keys to scroll through previously executed commands.
  • History is persisted between sessions by saving it to a file at ~/.myshell_history.

Arithmetic Evaluation

• Built-in Calculator: MyShell can evaluate arithmetic expressions directly typed into the prompt.
  • Supports integers and floating-point numbers (printed to two decimal places if not a whole number).
  • Supported operators include addition (+), subtraction (-), multiplication (*), division (/), modulo (%), and exponentiation (^).
  • Supports parentheses for defining order of operations35].

Built-in Commands

MyShell includes its own set of essential built-in commands for core shell functionality:

Command	Description	Source
cd <directory>	Changes the current working directory.	Built-in
exit	Closes MyShell and returns to the calling shell[cite: 12].	Built-in
help	Displays this comprehensive help message listing all features and built-in commands[cite: 13, 14].	Built-in

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⚙️ Installation

The installation process compiles the MyShell source code from the GitHub repository and installs the resulting binary to /usr/local/bin. You must have git and gcc installed.

Prerequisites

• git: For cloning the repository.
• gcc (GNU Compiler Collection): For compiling the C source code.
• sudo privileges: Required to install the binary to /usr/local/bin.

Installation Steps (Using install.sh)

1. Download the Installation Script:

   wget https://raw.githubusercontent.com/Bimbok/myshell/main/install.sh -O install.sh
   chmod +x install.sh

2. Run the Installer with sudo:

   sudo ./install.sh

   This script will perform the following actions:
   • Check for sudo privileges.
   • Clone the source code from https://github.com/Bimbok/myshell.git into a temporary directory (/tmp/myshell-install).
   • Compile myshell.c using gcc.
   • Copy the compiled binary (myshell) to /usr/local/bin.
   • Clean up the temporary files.

Post-Installation

After installation, you can run MyShell by simply typing:

myshell

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🔧 Uninstalling MyShell

The uninstallation script removes the binary and cleans up the system-wide configuration, but intentionally preserves your personal history file for safety.

Uninstallation Steps (Using uninstall.sh)

1. Download the Uninstallation Script:

   wget https://raw.githubusercontent.com/Bimbok/myshell/main/uninstall.sh -O uninstall.sh
   chmod +x uninstall.sh

2. Run the Uninstaller with sudo:

   sudo ./uninstall.sh

   This script will perform the following actions:
   • Check for sudo privileges.
   • Check Login Shell: It checks if the user running the script is currently using MyShell as their login shell. If so, it issues a critical warning and prompts for confirmation to prevent the user from being locked out of their system.
   • Remove the MyShell binary from /usr/local/bin/myshell.
   • Remove the MyShell path (/usr/local/bin/myshell) from the system-wide /etc/shells file, creating a backup first.
   • Inform the user that the personal history file (~/.myshell_history) was not removed.

Manual Cleanup

If you wish to completely remove all traces of MyShell, manually delete the history file:

rm -f ~/.myshell_history

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🛠️ Installation Parameters (install.sh)

The install.sh script supports a specific parameter for system configuration:

Parameter	What it Does
--set-login	This option only modifies the system shell list[cite: 216]. It adds the MyShell binary path (/usr/local/bin/myshell) to the /etc/shells file.
No Parameter	Runs the primary installation process: clones, compiles, and installs the binary to /usr/local/bin.

How to Use --set-login

Run the command below after the binary has been successfully installed. This step is necessary if you intend to use MyShell as your default login shell (e.g., via chsh):

sudo ./install.sh --set-login

To then make MyShell your default login shell, use chsh:

chsh -s /usr/local/bin/myshell

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📝 Usage

MyShell operates like any standard Unix shell.

Executing Commands

Type the command and its arguments, then press Enter:

myshell $ ls -l | grep txt > output.txt

Arithmetic Evaluation

Type the full expression and press Enter. MyShell detects the arithmetic pattern and evaluates it instead of executing a program[cite: 186].

myshell $ 10 + 5 * (8/4)
30
myshell $ 2^8 - 1
255

Tab Completion

1. Command Completion: Type the start of a command and press TAB:

   myshell $ help  # Press TAB after 'h'

   (This would complete to help or show options like history, etc., if they existed.)

2. File/Directory Completion: Type the start of a file path (or a path starting with ./, /, or ~) and press TAB[cite: 103].

   myshell $ cat outpu  # Press TAB after 'outpu' to complete to 'output.txt'