UNIQ(1) General Commands Manual UNIQ(1)

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:

, --count
Precede each output line with the count of the number of times the line occurred in the input, followed by a single space.
, --repeated
Output a single copy of each line that is repeated in the input. Ignored if -D is also specified.
, --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.
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.
, --ignore-case
Case insensitive comparison of lines.
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.
, --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 uniq utility exits 0 on success, and >0 if an error occurs.

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

Madrid
Lisbon
Madrid

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

$ uniq -u cities.txt
Madrid
Lisbon
Madrid

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:

madrid
Madrid
Lisbon

Show repeated lines ignoring case sensitiveness:

$ uniq -d -i cities.txt
madrid

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

$ uniq -D -i cities.txt
madrid
Madrid

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

sort(1)

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

A uniq command appeared in Version 3 AT&T UNIX.

January 12, 2024 macOS 15.0