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| Chapter 2 UNIX Commands |

## uniq

    uniq [options] [file1 [file2]]

Remove duplicate adjacent lines from sorted `file1`, sending one copy of each line to `file2` (or to standard output). Often used as a filter. Specify only one of -c, -d, or -u. See also comm and sort.

### Options

-c

  Print each line once, counting instances of each.

-d

  Print duplicate lines once, but no unique lines.

-u

  Print only unique lines (no copy of duplicate entries is kept).

-`n`

  Ignore first `n` fields of a line. Fields are separated by spaces or by tabs.

+`n`

  Ignore first `n` characters of a field.

### Examples

Send one copy of each line from list to output file list.new:

>     uniq list list.new

Show which names appear more than once:

>     sort names | uniq -d

Show which lines appear exactly three times:

>     sort names | uniq -c | grep "3 "

Reference: unget |  | Reference: units