This repository explains how to configure a custom merge driver in Git, allowing a custom tool to be run whenever certain files are caught in a merge conflict.

Run example.sh for a demonstration of the merge driver. It will create a merge conflict in the repository, causing the merge driver to start and resolve the conflict.

First up is defining the merge driver. This is done in the .git/config file:

[merge "my-custom-driver"]
	name = A custom merge driver used to resolve conflicts in certain files
	driver = my-merge-tool.sh %O %A %B

The merge block contains the merge driver's identifier, used to reference the merge driver later.

The name property contains a description of the merge driver.

The driver property contains the command that will be called when a conflict occurs. There's a handful of predefined parameters, most notably:

• %O: ancestor’s version of the conflicting file
• %A: current version of the conflicting file
• %B: other branch's version of the conflicting file

For more, visit git-scm.com - Git Attributes.

Note that, much like git hooks, the .git/config file can't be checked in/shared through the repository. A common way of distributing merge drivers is to check the configuration file in elsewhere and provide a script to copy it to .git/config. In this repository, the merge driver is configured in the .gitconfig file, which is copied to .git/config by the mergetool-setup.sh script.

For a successful merge, the merge driver is expected to leave the merge result at %A's path and exiting with status code 0.

If the merge went awry, the merge driver can exit with a non-zero status code.

Note: Any tools or scripts called by the merge driver must be available on PATH.

You configure the file patterns you want the merge driver to be used for in the .gitattributes file:

*.mrg merge=my-custom-driver

• git-scm.com - Git Attributes
• stackoverflow.com - 'How do I add a custom merge strategy?'
• stackoverflow-com - 'Add a git merge driver to the repository'