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.\"	$OpenBSD: uniq.1,v 1.22 2021/11/02 15:12:09 millert Exp $
.\"	$NetBSD: uniq.1,v 1.5 1994/12/06 07:51:15 jtc Exp $
.\"
.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 3. Neither the name of the University nor the names of its contributors
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.\"     @(#)uniq.1	8.1 (Berkeley) 6/6/93
.\"
.Dd $Mdocdate: November 2 2021 $
.Dt UNIQ 1
.Os
.Sh NAME
.Nm uniq
.Nd report or filter out repeated lines in a file
.Sh SYNOPSIS
.Nm uniq
.Op Fl ci
.Op Fl d | u
.Op Fl f Ar fields
.Op Fl s Ar chars
.Oo
.Ar input_file
.Op Ar output_file
.Oc
.Sh DESCRIPTION
The
.Nm
utility reads the standard input comparing adjacent lines and writes
a copy of each unique input line to the standard output.
The second and succeeding copies of identical adjacent input lines are
not written.
Repeated lines in the input will not be detected if they are not adjacent,
so it may be necessary to sort the files first.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl c
Precede each output line with the count of the number of times the line
occurred in the input, followed by a single space.
.It Fl d
Only output lines which have duplicates.
.It Fl f Ar fields
Ignore the first
.Ar fields
in each input line when doing comparisons.
A field is a string of non-blank characters separated from adjacent fields
by blanks, with blanks considered part of the following field.
Field numbers are one based, i.e., the first field is field one.
.It Fl i
Regard lower and upper case ASCII characters as identical.
.It Fl s Ar chars
Ignore the first
.Ar chars
characters in each input line when doing comparisons.
If specified in conjunction with the
.Fl f
option, the first
.Ar chars
characters after the first
.Ar fields
fields will be ignored.
Character numbers are one based, i.e., the first character is character one.
.It Fl u
Only output lines which are unique.
.\".It Fl Ns Ar n
.\"(Deprecated; replaced by
.\".Fl f ) .
.\"Ignore the first n
.\"fields on each input line when doing comparisons,
.\"where n is a number.
.\"A field is a string of non-blank
.\"characters separated from adjacent fields
.\"by blanks.
.\".It Cm \&\(pl Ns Ar n
.\"(Deprecated; replaced by
.\".Fl s ) .
.\"Ignore the first
.\".Ar m
.\"characters when doing comparisons, where
.\".Ar m
.\"is a
.\"number.
.El
.Pp
If additional arguments are specified on the command line, the first
such argument is used as the name of an input file, the second is used
as the name of an output file.
A file name of
.Ql -
denotes the standard input or the standard output
.Pq depending on its position on the command line .
.Sh ENVIRONMENT
.Bl -tag -width LC_CTYPE
.It Ev LC_CTYPE
The character encoding
.Xr locale 1 .
It decides which byte sequences form characters
and which characters are considered blank.
If unset or set to
.Qq C ,
.Qq POSIX ,
or an unsupported value, each byte is treated as a character,
and only space and tab are considered blank.
.Pp
This variable is ignored for case comparisons.
Lower and upper case versions of non-ASCII characters are always
considered different.
.El
.Sh EXIT STATUS
.Ex -std uniq
.Sh SEE ALSO
.Xr sort 1
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The
.Fl i
option and the use of
.Fl c
in conjunction with
.Fl d
or
.Fl u
are extensions to that specification.
.Pp
The historic
.Cm + Ns Ar number
and
.Fl Ns Ar number
options have been deprecated but are still supported in this implementation.
.Sh HISTORY
A
.Nm
utility first appeared in
.At v3 .