I really hate visualizing diffs using the default UNIX
git mergetool myfile.txt
You could use
opendiff. It is a command line tool which opens the GUI of FileMerge.
You could instruct Git to use it automatically for
git config --global merge.tool opendiff
If you want it for
git-difftool as well:
git config --global diff.tool opendiff
And you could also disable the prompting for every file with:
git config --global difftool.prompt false
For more details type:
git help config and search with
/ for the different options.
P.S. If you don't have
opendiff installed you could install it together with the Developer Tools from XCode: https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/opendiff.1.html
UPDATE: In recent versions of XCode, FileMerge is now bundled with XCode. You cannot install FileMerge as a standalone program.
opendiff is still in its command-line utilities which are standalone.