Compare two files with FileMerge
If you’re a developer and you haven’t found out about FileMerge yet, you are missing out on one of the more useful apps included within Apple’s XCode installation. FileMerge lets you select any two files and it will compare the two, pointing out any differences between the files. If you’re a developer you already know why this is wildly useful, as it makes tracking down major and minor code changes remarkably easy. Apparently FileMerge is a survivor from the days of NeXTStep, and once you see how useful it is, you’ll see why it was saved and bundled with XCode.
XCode can be installed from the CD/DVD’s included with your Mac, or downloaded for free from the Apple Developer site. Once XCode has been installed, FileMerge will be located at /Developer/Applications/Utilities/FileMerge
[ FileMerge screenshot from Schwehr.org ]