I need a free duplicate file finder/remover app, with ability to find duplicate files/folders by name and/or by size and to remove one of duplicates.
I have tried literally dozens of duplicate file finders (I still have the installers/ZIP files for about 20 of them sitting around). I used CloneMaster 2.19 for a time because it was the best one I could find, though even that wans’t perfect (I wanted one that could also detect duplicate MP3s by audio content, ignoring the tags). All of them had problems that frustrated me enough that I decided to write my own and laid out a list of the features I demand of a DFF.
And then I found AllDup . It is the first and only one that actually made me abandon a project (technically mine isn’t completely abandoned, it’s just no longer being worked on since I don’t need to write it anymore because AllDup does everything I want of it). Anyway, AllDup searches for duplicate files, but unlike the others, it uses a lot of the tricks and techniques that I was going to use in my own DFF. As such, it is very fast: it can for example scan >250,000 of sizes from 1B-5GB in ~30mins (I have done it on my system several times).
Another great (and for some reason rare) feature of AllDup is as I mentioned that it can scan for duplicate MP3s by their actually audio data while ignoring tags, so two MP3s that are the same but have differing tags (very common when downloading) will be detected as duplicates. (It could even detect when I ripped two identical songs from two different CDs—with different tags of course.) Of course it can detect dupes based on other factors besides byte-for-byte content, like filenames, dates, etc.
Other great features of AllDup include the ability to filter (include or exclude) based on filename and/or folder name and/or filesize. The results screen is also very versatile with options to select files based on date, path, name, this, that, the other… It also has variety in what to do with detected duplicates
Michael Thummerer is also very receptive. I have reported bugs and suggested features to him several times which he addressed extremely quickly (to the point that he told me to download and try out a beta with the updates in the very next emails the same day).
Oh and it’s free.
Duplicate Cleaner  is very fast and it has extensive result set filtering possibilities. http://www.digitalvolcano.co.uk/content/duplicate-cleaner
There was this Duplicate File Finder available for some time but now its only on secondary sites, like this Softpedia reference .
The Wareseeker site shows the correct reference
http://dff.nazrashid.com/ which is no longer around. I would be careful fetching executables from such sites though.
It can do search for duplicates within multiple directory trees based on,
And, it lets you filter your search by a minimum and maximum files size (speeds up things when you know the bounds).
A very thoughtful piece of software. Don't know if there is something as fast and featured for free around these days.
The comments refer to a similar Sourceforge tool called Doubles  http://www.softpedia.com/get/System/File-Management/Duplicate-File-Finder.shtml
I find this very helpful and more useful than doublekiller. A particularly nice feature is the "Pools" feature, where you can compare one group of directories with another group of directories while ignoring duplicates within the groups.
For example, my partner likes to keep duplicate image files while working with images. I want to see if I have any copies of those files in my directories.
Pool 1 - Partner Home Directory Pool 2 - My Home Directory.
The only duplicates found are if a file is present both in my directories and my partner's directories. The files only duplicated in my partner's directories are ignored.
I have the following batch file lying around for some time:
@ECHO OFF REM TODO: Help when run with /? and switch for recursion REM Furthermore check whether we might have enough files to hit the envvar length limit REM and switch strategies accordingly (slower but finds all dupes then) SETLOCAL ENABLEEXTENSIONS ENABLEDELAYEDEXPANSION REM This method speeds up comparison but suffers from long file lists REM as environment variables have a length limit SET FILELIST= FOR %1 %%i IN (*) DO ( FOR %%j IN (!FILELIST!) DO ( IF %%~zi EQU %%~zj ( fc /b "%%~i" "%%~j">NUL && echo "%%~i" = "%%~j" ) ) SET FILELIST=!FILELIST! "%%~i" ) ENDLOCAL GOTO :EOF
You can run it with
/r as argument to run recursively through the directory tree.
Total Commander  has a brilliant duplicate file finder utility. Unfortunately it is not free.
As nik mentioned there is the Duplicate File Finder which is open source and cross platform. It's available on SourceForge here  http://www.ghisler.com/
DoubleKiller is an excellent free (they also have a pro version) duplicate file finder/remover. I've been using it for years and would thoroughly recommend it.
Compare very similar directories, perhaps between your "Documents" folder and your impromptu "backup", "Copy of Documents" folder, you created several weeks ago "just in case".
You can figure out what files are still identical, which files are the newest (or oldest, if you have encountered a problem), and which files exist only in one place. Then you can "merge" the directories and delete the duplicates.
Duplocator . A cross-platform duplicate-finding python script. http://brainerror.net/scripts/python/duplocator/
Advanced system care free  comes with an Clone Files Finder with the program. I use it, and it works fine. http://www.iobit.com/advancedwindowscareper.html
It displays the files in easy-to-see groups isolated by color. It warns you if you've marked all the copies of a file for deletion, can automark them, can selectively automark all files in a directory (I used this a lot), can delete directories that become empty after the deletions, etc. Be careful of links if you're using it in Wine. It will delete all copies of a file without knowing that they are links. http://www.geocities.com/hirak_99/goodies/finddups.html
Fast Duplicate File Finder:
I have found Yet Another Duplicate File Remover  to be awesome. It is pretty new and very easy to use. I used it to compare over 50,000 files from a hard drive recovery project, so it can handle a large amount of files. http://sourceforge.net/projects/yadfr/
The best solution I tested on windows was the already mentioned Alldup . Props to Synetech inc. for sharing it. Brilliant and very professional freeware tool.
In the post I provide tested bash solutions that will work under Cygwin, Linux and OS X (or anything that uses bash-like shell).
* Comparison to other duplicate finding utilities: + Very fast + Comparing directories too. + Often, two directories contain, let's say, 4 equal files and 5th file is different. We handle it too and output these as "common files in directories" + Absence of unnecessary switches. - Win32 only - Command-line only