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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  succeeding  copies  of  repeated  adjacent
       input lines shall not be written.

       Repeated lines in the input shall not be detected if they are not adjacent.

OPTIONS

       The  uniq  utility  shall  conform to the Base Definitions volume of IEEE Std 1003.1-2001,
       Section 12.2, Utility Syntax Guidelines.

       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 comparison.

       -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 specified 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 variables that  are  unset  or
              null.  (See  the  Base  Definitions  volume  of  IEEE Std 1003.1-2001, Section 8.2,
              Internationalization Variables 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 current
              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 only if no output_file operand  is  specified.  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 foo0
               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, comparing 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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       comm , sort

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .