Script to run meld by default on git diff's (~/.git_meld_diff.js)

gistfile1.txt

#!/usr/bin/env node
    var exec = require('child_process').exec;

    function cb(error, stdout, stderr) {
       if (error !== null) {
          console.log('exec error: ' + error);
       }
    }
    exec('/usr/bin/meld ' + process.argv[3] + ' ' + process.argv[2] , cb);

Save this as `~/.git_meld_diff.js` and then run `$ git config --global diff.external ~/.git_meld_diff.js`