Linux Shells by Example

uniq—reports on duplicate lines in a file

uniq [ [ –u ] [ –d ] [ –c ] [ +n ] [ –n ] ] [ input [ output ] ]

uniq reads the input file, comparing adjacent lines. In the normal case, the second and succeeding copies of repeated lines are removed; the remainder is written on the output file. Input and output should always be different.

Example A.69.

1 uniq file1 file2 2 uniq -d -2 file3

Explanation

1. Removes duplicate adjacent lines from file1 and puts output in file2.

2. Displays the duplicate lines where the duplicate starts at third field.