tail head cat sleep
QR code linking to this page

Manual Pages  — UNIQ


uniq – report or filter out repeated lines in a file



uniq [-c] [-d | -u] [-i] [-f num] [-s chars] [ input_file [output_file] ]


The uniq utility reads the specified input_file comparing adjacent lines, and writes a copy of each unique input line to the output_file. If input_file is a single dash ('-') or absent, the standard input is read. If output_file is absent, standard output is used for output. The second and succeeding copies of identical adjacent input lines are not written. Repeated lines in the input will not be detected if they are not adjacent, so it may be necessary to sort the files first.

The following options are available:
  Precede each output line with the count of the number of times the line occurred in the input, followed by a single space.
  Only output lines that are repeated in the input.
-f num
  Ignore the first num fields in each input line when doing comparisons. A field is a string of non-blank characters separated from adjacent fields by blanks. Field numbers are one based, i.e., the first field is field one.
-s chars
  Ignore the first chars characters in each input line when doing comparisons. If specified in conjunction with the -f option, the first chars characters after the first num fields will be ignored. Character numbers are one based, i.e., the first character is character one.
  Only output lines that are not repeated in the input.
  Case insensitive comparison of lines.


The LANG, LC_ALL, LC_COLLATE and LC_CTYPE environment variables affect the execution of uniq as described in environ(7).


The utility exits 0 on success, and >0 if an error occurs.


The historic +number and number options have been deprecated but are still supported in this implementation.




The uniq utility conforms to IEEE Std 1003.1-2001 ("POSIX.1") as amended by Cor. 1-2002.


A uniq command appeared in AT&T v3 .

UNIQ (1) May 15, 2017

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

The wonderful thing about standards is that there are so many of them to choose from.
— Grace Murray Hopper