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 | -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:
-c -, --count
  Precede each output line with the count of the number of times the line occurred in the input, followed by a single space.
-d -, --repeated
  Output a single copy of each line that is repeated in the input.
-D -, --all-repeated [septype]
  Output all lines that are repeated (like -d, but each copy of the repeated line is written). The optional septype argument controls how to separate groups of repeated lines in the output; it must be one of the following values:

none Do not separate groups of lines (this is the default).
prepend Output an empty line before each group of lines.
separate Output an empty line after each group of lines.
-f num , --skip-fields 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.
-i -, --ignore-case Case insensitive comparison of lines.
-s chars , --skip-chars chars Ignore the first chars characters in each input line when doing comparisons. If specified in conjunction with the -f -, --unique 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.
-u -, --unique Only output lines that are not repeated in the input.


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.


Assuming a file named cities.txt with the following content:

The following command reports three different lines since identical elements are not adjacent:

$ uniq -u cities.txt

Sort the file and count the number of identical lines:

$ sort cities.txt | uniq -c
        1 Lisbon
        2 Madrid

Assuming the following content for the file cities.txt:


Show repeated lines ignoring case sensitiveness:

$ uniq -d -i cities.txt

Same as above but showing the whole group of repeated lines:

$ uniq -D -i cities.txt

Report the number of identical lines ignoring the first character of every line:

$ uniq -s 1 -c cities.txt
        2 madrid
        1 Lisbon


The historic amp;+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.amp; 1-2002.


A uniq command appeared in AT&T v3 .

UNIQ (1) June 7, 2020

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 most horrifying thing about Unix is that, no matter how many times you hit yourself over the head with it, you never quite manage to lose consciousness. It just goes on and on.
— Patrick Sobalvarro