SAMEFILE(1)

NAME
samefile - find identical files

SYNOPSIS
samefile

DESCRIPTION
samefile reads a list of file names (one file name per line) from stdin. For each file name pair with identical contents, a line consisting of six tab separated fields is output: The size in bytes, two file names, the character ``='' if the two files are on the same device, ``X'' otherwise, and the link counts of the two files. The output is sorted in reverse order by size. samefile uses two stages to give optimum performance.

In the first stage, all non-plain files are silently ignored (directories, devices, FIFOs, sockets, symbolic links) as well as files for which stat(2) or open(2) fails. The result of the first stage (the file names) is written into a binary tree with one node for every file size. Each node is in turn a linked list of file names along with inode and device information. It is also at this first stage where checks for hard links are done. For any inode only one filename will be added to the binary tree. In the second stage all files having the same size are compared against each other. The rules of mathematical logic are applied to reduce work and output noise: if files A, B, and C have the same size and samefile finds that A = B and A = C then it will not compare B against C (and will not output a line for B and C) but only for A = B and A = C. The algorithm will detect equality across arbitrarily long chains. Note however, that because only the first filename per inode gets into the first stage, the output for a group of identical files with different inode numbers is also minimized. Suppose you have six identical files of size 100 in an inode group consisting of the three inodes with numbers 10, 20 and 30:

$ ls -i   # output edited for readabilty:
   10 file1     20 file4     30 file6
   10 file2     20 file5
   10 file3
$ ls | samefile
100     file1   file4   =       3       2
100     file1   file6   =       3       1

The sum of the sizes in the first column is the amount of disk space you could gain by making all 6 files links to only one file or remove all but one of the files. To be precise, disk space is allocated in blocks - you will probably gain two blocks here, rather than 200 bytes. Note that it is not enough to just remove file4 and file6 (you would gain only 100 bytes because file5 still exists.)

LIMITATIONS
Samefile was written with no limits in mind. The number of input lines is unlimited. The size of the actual files is only limited by available virtual memory needed to compare one pair of files. The only hard limit is the constraint that there should not be more than about 8192 files having the same size. Experience has shown that there are rarely more than a couple dozen files of the same size.

EXAMPLES
For everybody:
What are the duplicates under my home directory?
    $ find $HOME | samefile
For the sysadmin folks:
Report all duplicate files under /usr larger than 16k:
    $ find /usr -size +16384c -a -type f | samefile
For the ftp and WWW admins:
How much space is wasted below our site's /pub directory?
    $ find /pub -type f | samefile | awk '{sum += $1} END {print sum}'

EXIT STATUS
If samefile runs out of memory the exit status is 1, zero otherwise.

SEE ALSO
find(1), ln(1), rm(1)