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uniq is a Unix utility which, when fed a text file, outputs the file with adjacent identical lines collapsed to one.

First appearing in Version 3 Unix,^[1] it is a kind of filter program. Typically it is used after sort. It can also output only the duplicate lines (with the -d option), or add the number of occurrences of each line (with the -c option).

An example: To see the list of lines in a file, sorted by the number of times each occurs:

sort file | uniq -c | sort -n

Using uniq like this is common when building pipelines in shell scripts.

References

^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.

External links

[reader-1] McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.

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 Using uniq like this is common when building [[pipeline (software)|pipelines]] in [[shell script]]s.
-==Switches==
-*<tt>-u</tt>   Print only those lines which are not repeated (unique) in the input.
-*<tt>-d</tt>   Print only those lines which ''are'' repeated in the input.
-*<tt>-c</tt>   Generate an output report in default style except that each line is preceded by a count of the number of times it occurred.  If this option is specified, the <tt>-u</tt> and <tt>-d</tt> options are ignored if either or both are also present.
-*<tt>-i</tt>   Ignore case differences when comparing lines
-*<tt>-f</tt>   Ignore a number of fields in a line
-*<tt>-s</tt>   Skips a number of characters in a line
-*<tt>-w</tt>   Specifies the number of characters to compare in lines, after any characters and fields have been skipped
-*<tt>--help</tt>    Displays a help message
-*<tt>--version</tt> Displays version number on stdout and exits.
 ==See also==

v t e Unix command-line interface programs and shell builtins
File system	cat chattr chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask
Processes	at bg crontab fg kill nice ps time
User environment	env exit logname mesg talk tput uname who write
Text processing	awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste patch printf read sed sort strings tail tr troff uniq vi wc xargs
Shell builtins	alias cd echo test unset wait
Searching	find grep
Documentation	man
Software development	ar ctags lex make nm strip yacc
Miscellaneous	bc cal expr lp od sleep true and false
Categories Standard Unix programs Unix SUS2008 utilities List