As much as we love feature-packed applications that perform countless tasks, there's nothing wrong with an inexpensive utility that does the one thing we need without much fuss and bother. Such is Fiplab's $5 (currently on sale for $3) Duplicate Detective (Mac App Store link). As its name implies, it exists to locate duplicate files on your Mac and then, if you wish, fling them into the Trash.
Duplicate Detective does its work in a simple way. Just launch the application, and then drag a folder or volume into the utility's window. Duplicate Detective scans that folder or volume, and then lets you know how many duplicates it finds. What it's specifically looking for are exact duplicates by comparing each file's hash strings. If the strings match up, you have a duplicate; if they don't — if one file is a PNG version of an image and the other a JPEG — the files are not included in the duplicate tally.
If you have a lot of files — say, hundreds of thousands, as could easily be the case with a large hard drive — this can take a very long time. If you'd like a faster result, scan a folder rather than an entire volume. (In a nice touch, when performing lengthy scans, the application displays humorous messages along the lines of "So, how's your day going?" to let you know that it hasn't locked up.)
When the job's done, you'll see the number of files scanned, the duplicate count, and the amount of storage space the superfluous files consume (thus giving you an idea of the amount of space you'll save if you delete the duplicates).
Click Next, and you'll see a list of duplicate groups on the left side of the window. (Each group contains all the duplicate versions of a particular file.) You can filter this list, using buttons at the top of the window, to display only folders, images, docs, audio files, archives (for example, .zip, .hqx, and .sit files), apps, or others. Select an item in the list and, to the right, a preview appears with the duplicates listed below — you can see the name of each, along each version's path, size, and modification date. (Duplicate Detective uses Quick Look to show previews. This means that for supported file types — image, audio, video, and text files, for example — you see a preview of the file's contents right in the Duplicate Detective window. For other types of files, you see a preview icon.)
Within the duplicate list you can choose to keep the newest or oldest version from within the selected group (based on modification date; if those are identical, the app uses the creation date). Alternatively, the Auto Select button automatically chooses either the newest or oldest version within each group. (You choose, in the app's Preferences window, whether Auto Select saves the newest or oldest version.)
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