.\" 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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.\" notice, this list of conditions and the following disclaimer.
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.\" notice, this list of conditions and the following disclaimer in the
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.\" may be used to endorse or promote products derived from this software
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.\" From: @(#)uniq.1 8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
.\"
.Dd June 7, 2020
.Dt UNIQ 1
.Os
.Sh NAME
.Nm uniq
.Nd report or filter out repeated lines in a file
.Sh SYNOPSIS
.Nm
.Op Fl c | Fl d | Fl D | Fl u
.Op Fl i
.Op Fl f Ar num
.Op Fl s Ar chars
.Oo
.Ar input_file
.Op Ar output_file
.Oc
.Sh DESCRIPTION
The
.Nm
utility reads the specified
.Ar input_file
comparing adjacent lines, and writes a copy of each unique input line to
the
.Ar output_file .
If
.Ar input_file
is a single dash
.Pq Sq Fl
or absent, the standard input is read.
If
.Ar output_file
is absent, standard output is used for 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 following options are available:
.Bl -tag -width Ds
.It Fl c , Fl -count
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 , Fl -repeated
Output a single copy of each line that is repeated in the input.
.It Fl D , Fl -all-repeated Op Ar septype
Output all lines that are repeated (like
.Fl d ,
but each copy of the repeated line is written).
The optional
.Ar septype
argument controls how to separate groups of repeated lines in the output;
it must be one of the following values:
.Pp
.Bl -tag -compact -width separate
.It none
Do not separate groups of lines (this is the default).
.It prepend
Output an empty line before each group of lines.
.It separate
Output an empty line after each group of lines.
.El
.It Fl f Ar num , Fl -skip-fields Ar num
Ignore the first
.Ar num
fields in each input line when doing comparisons.
A field is a string of non-blank characters separated from adjacent fields
by blanks.
Field numbers are one based, i.e., the first field is field one.
.It Fl i , Fl -ignore-case
Case insensitive comparison of lines.
.It Fl s Ar chars , Fl -skip-chars Ar chars
Ignore the first
.Ar chars
characters in each input line when doing comparisons.
If specified in conjunction with the
.Fl f , Fl -unique
option, the first
.Ar chars
characters after the first
.Ar num
fields will be ignored.
Character numbers are one based, i.e., the first character is character one.
.It Fl u , Fl -unique
Only output lines that are not repeated in the input.
.\".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
.Sh ENVIRONMENT
The
.Ev LANG ,
.Ev LC_ALL ,
.Ev LC_COLLATE
and
.Ev LC_CTYPE
environment variables affect the execution of
.Nm
as described in
.Xr environ 7 .
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Assuming a file named cities.txt with the following content:
.Bd -literal -offset indent
Madrid
Lisbon
Madrid
.Ed
.Pp
The following command reports three different lines since identical elements
are not adjacent:
.Bd -literal -offset indent
$ uniq -u cities.txt
Madrid
Lisbon
Madrid
.Ed
.Pp
Sort the file and count the number of identical lines:
.Bd -literal -offset indent
$ sort cities.txt | uniq -c
1 Lisbon
2 Madrid
.Ed
.Pp
Assuming the following content for the file cities.txt:
.Bd -literal -offset indent
madrid
Madrid
Lisbon
.Ed
.Pp
Show repeated lines ignoring case sensitiveness:
.Bd -literal -offset indent
$ uniq -d -i cities.txt
madrid
.Ed
.Pp
Same as above but showing the whole group of repeated lines:
.Bd -literal -offset indent
$ uniq -D -i cities.txt
madrid
Madrid
.Ed
.Pp
Report the number of identical lines ignoring the first character of every line:
.Bd -literal -offset indent
$ uniq -s 1 -c cities.txt
2 madrid
1 Lisbon
.Ed
.Sh COMPATIBILITY
The historic
.Cm \&\(pl Ns Ar number
and
.Fl Ns Ar number
options have been deprecated but are still supported in this implementation.
.Sh SEE ALSO
.Xr sort 1
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.1-2001
as amended by Cor.\& 1-2002.
.Sh HISTORY
A
.Nm
command appeared in
.At v3 .
