HOWTO: Using FileMerge (opendiff) with Git on OSX

howto-filemerge-git-osx.md

HOWTO: Using FileMerge (opendiff) with Git on OSX

FileMerge (opendiff) can really come in handy when you need to visually compare merging conflicts. Other times it's just a nice visual way to review your days work.

The following method works by creating a simple bash script (git-diff-cmd.sh) that sets us up with the proper command line arguments for Git to pass off files to FileMerge.

1. Open the bash script for editing:

    vi ~/bin/git-diff-cmd.sh
   

2. Paste the following code:

    #!/bin/sh 
    /usr/bin/opendiff "$2" "$5" -merge "$1"
   

3. Make the bash script executable:

    chmod +x ~/bin/git-diff-cmd.sh
   

4. Tell Git (globally) to run our bash script when 'git diff' is issued:

    git config --global diff.external ~/bin/git-diff-cmd.sh
   

5. Tell Git (globally) to opendiff during a 'git mergetool'

    git config --global merge.tool opendiff
   

Now head over to your Git-aware project directory and issue a git diff /path/to/modified/file.py and FileMerge will pop up showing you the differences against it and HEAD.

You can also do things like git diff --cached to review all the changes against HEAD.

If you get an error like:

    xcode-select: Error: No Xcode folder is set. Run xcode-select -switch <xcode_folder_path> 
    to set the path to the Xcode folder. Error: /usr/bin/xcode-select returned unexpected error.

Then run:

    sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer/

For reference: http://stackoverflow.com/questions/9300748/opendiff-does-not-start-anymore

Note for noobs like myself:
You don't have to work in ~/bin.

The directory you use here:
/Users/YOURS/git-diff-cmd.sh

must be the same as here:
git config --global diff.external /Users/YOURS/git-diff-cmd.sh

So you can do chmod without hassling with root rights and linux stuff.