chmodx

A lightweight, POSIX-compliant shell script to set file permissions using the familiar 10-character mode string seen in ls -l output.

The Problem

The standard chmod command uses either symbolic notation (u=rwx,g=rx,o=) or octal notation (755). Sometimes, it's more intuitive to copy the exact permission string you see in a long listing.

This tool allows you to do just that:

# Instead of this:
chmod u=rwx,g=rx,o= myfile
chmod 750 myfile

# You can do this:
chmodx -rwxr-x--- myfile

Features

• Intuitive Syntax: Use permission strings directly from ls -l.
• File Type Safety: Validates that the target is a file (-) or directory (d) as specified in the mode, preventing accidental mistakes.
• Verbose Mode: Use the --verbose flag to see a confirmation of the change and the equivalent chmod command.
• Robust & Portable: Written in pure POSIX sh, making it compatible with any Unix-like system (Linux, macOS, BSD).
• Comprehensive Error Checking: Validates input thoroughly and provides clear error messages.

Installation

1. Download the chmodx script.
2. Make it executable:

   chmod +x chmodx

3. Move it to a directory in your $PATH (e.g., ~/bin/ or /usr/local/bin/).

   sudo mv chmodx /usr/local/bin/

Usage

chmodx [--verbose] MODE FILE...

• MODE: A 10-character string.
  • Character 1: File type (- for file, d for directory).
  • Characters 2-10: Permissions for User, Group, and Other (each 3 chars). Each character must be r (read), w (write), x (execute), or - (no permission).
• FILE...: One or more files or directories to modify.

Examples

Set permissions for a file to rwxr-x--- (user: RWX, group: RX, other: none):

chmodx -rwxr-x--- my_script.sh

Set permissions for a directory to rwxr-xr-x and show the result:

chmodx --verbose drwxr-xr-x my_directory/
# Output:
# drwxr-xr-x 2 user group 4096 Jan 1 12:34 my_directory
# Reproduce with:
#   chmod 755 'my_directory'

How It Works

The script parses the 10-character string, validates it, and converts the 9 permission characters into a 3-digit octal number (e.g., rwxr-x--- becomes 750). It then uses the standard chmod command with this octal number to set the permissions. It includes safety checks to ensure the target file type matches the specified mode.

License

This project is released under the MIT License. Feel free to use, modify, and distribute it.

Contributing

Contributions are welcome! Please feel free to:

1. Open an issue to report a bug or suggest a new feature.
2. Submit a Pull Request with improvements.
   • Please ensure changes maintain POSIX sh compatibility.
   • Update tests and documentation as needed.