This article is about the Unix utility. For other uses, see Uniq (disambiguation).
uniq is a Unix utility which, when fed a text file, outputs the file with adjacent identical lines collapsed to one. 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.
-u Print only those lines which are not repeated (unique) in the input.,
-d Print only those lines which are repeated in the input.,
-c 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 -u and -d options are ignored if either or both are also present.,
-i Ignore case differences when comparing lines,
-f Ignore a number of fields in a line,
-s Skips a number of characters in a line,
-w Specifies the number of characters to compare in lines, after any characters and fields have been skipped,
--help Displays a help message,
--version Displays version number on stdout and exits.