Git: How to ignore file mode (chmod) changes

Introduction

Understanding how to configure Git to ignore file mode (chmod) changes is essential for developers working across different operating systems or in a collaborative environment with varying file permissions requirements. This tutorial delves into the basics, intermediate steps, and advanced configurations to manage file mode changes effectively in Git.

Git Tracks File Mode Changes by Default

In Unix-like operating systems, every file has a set of permissions that determine who can read, write, or execute it. The Git version control system tracks these permission changes by default, which can lead to unexpected diffs and commits if not properly managed. This guide will explain how to ignore file mode (chmod) changes in Git, thus ensuring a cleaner and more consistent repository.

Understanding Chmod

Before we proceed, it’s crucial to understand what ‘chmod’ stands for. Chmod, or ‘change mode,’ is a Unix command that sets the file permissions for user, group, and others on files and directories.

chmod u+x filename

The above command gives execute permission to the user who owns the file ‘filename’. Git tracks these changes by default.

Basic Configuration

To start, we’ll configure Git to ignore changes in file modes. The simplest way is to set the core.fileMode configuration setting to false.

git config core.fileMode false

By setting this configuration, Git will ignore file mode changes in your working directory. This can be applied to your local repository settings or across all repositories on your system by adding the global flag.

git config --global core.fileMode false

Intermediate Steps: Specific Scenarios

There are certain scenarios where you might need a fine-grained approach to handling file permissions.

Partial Permission Tracking

Suppose you only want to track the file mode changes of executables; you can create a custom Git hook to manage this.

Script for Managing Executable Tracking

#!/bin/sh
git diff --cached --name-only --diff-filter=A |
xargs -L 1 chmod +x

This script hooks into Git’s pre-commit process, affecting only newly added (‘A’ for added) files intended to be executables.

Advanced Configuration

For teams requiring a comprehensive solution, a combination of Git attributes and custom scripting may be necessary to handle complex permission changes.

Utilizing .gitattributes

You can use the .gitattributes file to ignore file mode changes on specific paths or files while allowing others.

echo "some/path/* -text" >> .gitattributes

This command appends a rule to .gitattributes file, which prevents Git from considering changes in the specified path as text changes, which includes permission modifications.

Advanced Hooks and Filters

Create custom filters and hooks to conditionally ignore or enforce mode changes.

#!/bin/sh

git config --get-regexp "^(svn|mercurial)" >/dev/null 2>&1 && {
    exit 0
}

# Your custom mode handling logic here

This script demonstrates how a hook could conditionally apply logic based on repository configuration settings, beyond just file modes.

Conclusion

Ignoring file mode changes in Git can help to maintain a clean and consistent codebase, especially while collaborating with a diverse team. By combining Git configurations and custom scripting, developers can tailor the handling of file permissions to their specific workflow requirements, contributing to smoother developer interactions and less noise in commit histories.