UNIQ

PROLOG

NAME

SYNOPSIS

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

DESCRIPTION

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

OPTIONS

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:]]*[ha[: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

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

INPUT FILES

ENVIRONMENT VARIABLES

LANG

Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, 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_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

STDOUT

STDERR

OUTPUT FILES

"%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

EXIT STATUS

 0

The utility executed successfully.

>0

An error occurred.

CONSEQUENCES OF ERRORS

The following sections are informative.  

APPLICATION USAGE

LC_ALL=C sort -u | sort

instead of:

sort | uniq

To remove duplicate lines based on whether they collate equally instead of whether they are identical, applications should use:

sort -u

instead of:

sort | uniq

When using uniq to process pathnames, it is recommended that LC_ALL, or at least LC_CTYPE and LC_COLLATE, are set to POSIX or C in the environment, since pathnames can contain byte sequences that do not form valid characters in some locales, in which case the utility's behavior would be undefined. In the POSIX locale each byte is a valid single-byte character, and therefore this problem is avoided.  

EXAMPLES

#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, 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

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

SEE ALSO

The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines  

COPYRIGHT

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.kernel.org/doc/man-pages/reporting_bugs.html .

Index

PROLOG

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

OPERANDS

STDIN

INPUT FILES

ENVIRONMENT VARIABLES

ASYNCHRONOUS EVENTS

STDOUT

STDERR

OUTPUT FILES

EXTENDED DESCRIPTION

EXIT STATUS

CONSEQUENCES OF ERRORS

APPLICATION USAGE

EXAMPLES

RATIONALE

FUTURE DIRECTIONS

SEE ALSO

COPYRIGHT