If you deal with duplicate files a lot, then fdupes is a very quick command-line solution. Among other things, it also does an MD5 comparison of file signatures, can recurse directories and following symlinks, and can be used for scripting as well as directly from standard input.
Bonaparte-Prime:/tmp $ fdupes -r -d ./
Set 1 of 4, preserve files [1 - 2, all]:
However, sometimes I forget what the hell foo.mp3 and bar/baz.mp3 really were. Then I have to fire up the Finder (or another Terminal window) and go chase down the file. What I really wanted would be if there were an “open one of these files and let me see what it is, then I’ll make a decision” option.
The beauty of open source is that I can patch fdupes myself and scratch this itch.
Finding the right app to hand off to might be annoying. On OS X, if you want to use the nice automagical way that Finder opens files (meaning that it generally knows what applications are appropriate to open an arbitrary file), you’ll have to link against LaunchServices, a part of the ApplicationServices framework. The code to do that is actually quite trivial. Simply add the ApplicationServices.h header, and then a function such as:
OSStatus open_target_file(const char* filepath)
err = FSPathMakeRef((const UInt8 *)filepath, &ref, &isDirectory);
err = LSOpenFSRef(&ref, NULL);
will do the job. Obviously this is simplistic and without error-checking, but you get the idea. LaunchServices will then handle the tedium of finding the right system application to launch the file.
The other half of the patch involves modifying fdupes’s command parser to take an additional variant. I chose a scheme by which if I precede the choice numbers I make with the character ‘o’, it should then hand off the filepath to the aforementioned open_target_file function and return to its previous state. Since the parser already has such a case to handle mistaken input, the patch is also quite simple. Simply check for ‘o’ in the first byte of the preservestr array at the appropriate place, and then should it match, have it execute open_target_file() rather than preserve[number] = 1; If you’re the portability stickler type, wrap these new lines under #ifdef __APPLE__ statements to check for OS X at compile-time.
Source code to simple utilities like these are really quite helpful. They let someone with just a modicum of programming ability tweak the behavior and address some common annoyances, without having re-invent the thing from scratch or to pester the original dev, who probably doesn’t care nearly enough about little features for specific platforms that only specific people might find useful. Write the extension code, create a patch, and keep your patch around in case the utility is ever updated. Scratch your own itch as free software intended.