Uniq

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. Be careful, uniq expects its input to be already sorted; sometimes sort -u is what you need.

Switches

• -u Print only lines which are not repeated in the original file
• -d Don't output lines that are not 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
• -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.

See also

• List of Unix programs

External links

• uniq's Linux manpage