Unix in a Nutshell, 4th Edition

Name

uniq

Synopsis

    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.

Common Options

-c, --count

Print each line once, counting instances of each.

-d, --repeated

Print duplicate lines once, but no unique lines.

-fn, --skip-fields=n

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

-sn, --skip-chars=n

Ignore first n characters of a field.

-u, --unique

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

- n

Like -f. This original, pre-POSIX syntax is deprecated; use -f instead.

+n

Like -s. This original, pre-POSIX syntax is deprecated; use -s instead.

GNU/Linux Options

-D, --all-repeated[=method]

Print all duplicate lines. -D takes no delimiter method. The delimiter method method describes how uniq should delimit groups of repeated lines in the output. It takes one of the values none (default), prepend (output a newline before each group), or separate (output a newline after each group).

-i, --ignore-case

Ignore case differences when checking for duplicates.

-wn, --check-chars=n

Compare only first n characters per line (beginning after skipped fields and characters).

Examples

Send one copy of each line from list to output file list.new (list must be sorted):

    uniq list list.new

Show which names appear more than once:

    sort names | uniq -d

Show which lines appear exactly three times:

 sort names | ...