man > uniq(1)

UNIQ(1)                                     User Commands                                    UNIQ(1)

NAME
       uniq - report or omit repeated lines

SYNOPSIS
       uniq [OPTION]... [INPUT [OUTPUT]]

DESCRIPTION
       Filter adjacent matching lines from INPUT (or standard input), writing to OUTPUT (or standard
       output).

       With no options, matching lines are merged to the first occurrence.

       Mandatory arguments to long options are mandatory for short options too.

       -c, --count
              prefix lines by the number of occurrences

       -d, --repeated
              only print duplicate lines, one for each group

       -D     print all duplicate lines

       --all-repeated[=METHOD]
              like   -D,   but   allow  separating  groups  with  an  empty  line;  METHOD={none(de‐
              fault),prepend,separate}

       -f, --skip-fields=N
              avoid comparing the first N fields

       --group[=METHOD]
              show  all  items,  separating  groups  with  an   empty   line;   METHOD={separate(de‐
              fault),prepend,append,both}

       -i, --ignore-case
              ignore differences in case when comparing

       -s, --skip-chars=N
              avoid comparing the first N characters

       -u, --unique
              only print unique lines

       -z, --zero-terminated
              line delimiter is NUL, not newline

       -w, --check-chars=N
              compare no more than N characters in lines

       --help display this help and exit

       --version
              output version information and exit

       A  field  is a run of blanks (usually spaces and/or TABs), then non-blank characters.  Fields
       are skipped before chars.

       Note: 'uniq' does not detect repeated lines unless they are adjacent.  You may want  to  sort
       the input first, or use 'sort -u' without 'uniq'.

AUTHOR
       Written by Richard M. Stallman and David MacKenzie.

REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT
       Copyright  ©  2023 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later
       <https://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY,  to
       the extent permitted by law.

SEE ALSO
       comm(1), join(1), sort(1)

       Full documentation <https://www.gnu.org/software/coreutils/uniq>
       or available locally via: info '(coreutils) uniq invocation'

GNU coreutils 9.4                           January 2026                                     UNIQ(1)