DuFF is Unix command-line utility for quickly finding duplicates in a given set of files. Duff is written in C, licensed under the zlib/libpng license and should compile and build on most modern Unix systems, any with a C89 compiler. It uses gettext where available, but will work without it. The following distributions and package systems already carry duff packages:

ALT Linux Arch Linux Cygwin Debian GNU/Linux Fink FreeBSD Gentoo Linux Homebrew MacPorts NetBSD (in WIP) openSUSE Parabola GNU/Linux Slackware Linux Ubuntu