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UNIQ(1P)		   POSIX Programmer's Manual		      UNIQ(1P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       uniq — report or filter out repeated lines in a file

SYNOPSIS
       uniq [−c|−d|−u] [−f fields] [−s char] [input_file [output_file]]

DESCRIPTION
       The uniq utility shall read an input file comparing adjacent lines, and
       write  one  copy	 of each input line on the output. The second and suc‐
       ceeding copies of repeated adjacent input lines shall not  be  written.
       The  trailing <newline> of each line in the input shall be ignored when
       doing comparisons.

       Repeated lines in the input shall not be detected if they are not adja‐
       cent.

OPTIONS
       The  uniq  utility  shall  conform  to  the  Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except that  '+'
       may be recognized as an option delimiter as well as '−'.

       The following options shall be supported:

       −c	 Precede  each output line with a count of the number of times
		 the line occurred in the input.

       −d	 Suppress the writing of lines that are not  repeated  in  the
		 input.

       −f fields Ignore	 the first fields fields on each input line when doing
		 comparisons, where fields is a positive  decimal  integer.  A
		 field	is  the	 maximal  string  matched by the basic regular
		 expression:

		     [[:blank:]]*[^[:blank:]]*

		 If the fields	option-argument	 specifies  more  fields  than
		 appear on an input line, a null string shall be used for com‐
		 parison.

       −s chars	 Ignore the first chars	 characters  when  doing  comparisons,
		 where chars shall be a positive decimal integer. If specified
		 in conjunction with the −f option, the first chars characters
		 after	the first fields fields shall be ignored. If the chars
		 option-argument specifies more characters than remain	on  an
		 input line, a null string shall be used for comparison.

       −u	 Suppress the writing of lines that are repeated in the input.

OPERANDS
       The following operands shall be supported:

       input_file
		 A  pathname  of  the input file. If the input_file operand is
		 not specified, or if the  input_file  is  '−',	 the  standard
		 input shall be used.

       output_file
		 A  pathname of the output file. If the output_file operand is
		 not specified, the standard output shall be used. The results
		 are  unspecified if the file named by output_file is the file
		 named by input_file.

STDIN
       The standard input shall be used only if no input_file operand is spec‐
       ified or if input_file is '−'.  See the INPUT FILES section.

INPUT FILES
       The input file shall be a text file.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of uniq:

       LANG	 Provide  a  default  value for the internationalization vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables for the precedence  of  internationalization  variables
		 used to determine the values of locale categories.)

       LC_ALL	 If  set  to  a non-empty string value, override the values of
		 all the other internationalization variables.

       LC_COLLATE
		 Determine the locale for ordering rules.

       LC_CTYPE	 Determine the locale for the interpretation of	 sequences  of
		 bytes of text data as characters (for example, single-byte as
		 opposed to  multi-byte	 characters  in	 arguments  and	 input
		 files)	 and which characters constitute a <blank> in the cur‐
		 rent locale.

       LC_MESSAGES
		 Determine the locale that should be used to affect the format
		 and  contents	of  diagnostic	messages  written  to standard
		 error.

       NLSPATH	 Determine the location of message catalogs for the processing
		 of LC_MESSAGES.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The  standard  output shall be used if no output_file operand is speci‐
       fied, and shall be used if the  output_file  operand  is	 '−'  and  the
       implementation  treats  the  '−' as meaning standard output. Otherwise,
       the standard output shall not be used.  See the OUTPUT FILES section.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       If the −c option is specified, the output file shall be empty  or  each
       line shall be of the form:

	   "%d %s", <number of duplicates>, <line>

       otherwise,  the output file shall be empty or each line shall be of the
       form:

	   "%s", <line>

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0    The utility executed successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       The sort utility can be used to cause repeated lines to be adjacent  in
       the input file.

EXAMPLES
       The  following  input  file data (but flushed left) was used for a test
       series on uniq:

	   #01 foo0 bar0 foo1 bar1
	   #02 bar0 foo1 bar1 foo1
	   #03 foo0 bar0 foo1 bar1
	   #04
	   #05 foo0 bar0 foo1 bar1
	   #06 foo0 bar0 foo1 bar1
	   #07 bar0 foo1 bar1 foo0

       What follows is a series of test invocations of the uniq	 utility  that
       use  a mixture of uniq options against the input file data. These tests
       verify the meaning of adjacent.	The uniq utility views the input  data
       as  a  sequence	of  strings  delimited	by '\n'.  Accordingly, for the
       fieldsth member of the sequence, uniq  interprets  unique  or  repeated
       adjacent lines strictly relative to the fields+1th member.

	1. This	 first	example tests the line counting option, comparing each
	   line of the input file data starting from the second field:

	       uniq −c −f 1 uniq_0I.t
		   1 #01 foo0 bar0 foo1 bar1
		   1 #02 bar0 foo1 bar1 foo1
		   1 #03 foo0 bar0 foo1 bar1
		   1 #04
		   2 #05 foo0 bar0 foo1 bar1
		   1 #07 bar0 foo1 bar1 foo0

	   The number '2', prefixing the fifth line of output, signifies  that
	   the uniq utility detected a pair of repeated lines. Given the input
	   data, this can only be true when uniq is run using the −f 1	option
	   (which  shall  cause	 uniq  to ignore the first field on each input
	   line).

	2. The second example tests the option to suppress unique lines,  com‐
	   paring  each	 line  of the input file data starting from the second
	   field:

	       uniq −d −f 1 uniq_0I.t
	       #05 foo0 bar0 foo1 bar1

	3. This test suppresses repeated lines, comparing  each	 line  of  the
	   input file data starting from the second field:

	       uniq −u −f 1 uniq_0I.t
	       #01 foo0 bar0 foo1 bar1
	       #02 bar0 foo1 bar1 foo1
	       #03 foo0 bar0 foo1 bar1
	       #04
	       #07 bar0 foo1 bar1 foo0

	4. This suppresses unique lines, comparing each line of the input file
	   data starting from the third character:

	       uniq −d −s 2 uniq_0I.t

	   In the last example, the uniq utility found no input	 matching  the
	   above criteria.

RATIONALE
       Some  historical implementations have limited lines to be 1080 bytes in
       length, which does not meet the implied {LINE_MAX} limit.

       Earlier versions of this	 standard  allowed  the	 −number  and  +number
       options.	 These options are no longer specified by POSIX.1‐2008 but may
       be present in some implementations.

FUTURE DIRECTIONS
       None.

SEE ALSO
       comm, sort

       The Base Definitions volume of  POSIX.1‐2008,  Chapter  8,  Environment
       Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			      UNIQ(1P)
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