uniq (1p) - Linux Man Pages
uniq: report or filter out repeated lines in a file
PROLOGThis 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.
uniq - report or filter out repeated lines in a file
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.
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:
- Precede each output line with a count of the number of times the line occurred in the input.
- Suppress the writing of lines that are not repeated in the input.
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
If the fields option-argument specifies more fields than appear on an input line, a null string shall be used for comparison.
- 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.
Suppress the writing of lines that are repeated in the input.
The following operands shall be supported:
- 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.
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.
The following environment variables shall affect the execution of uniq:
- 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.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
Determine the locale for ordering rules.
- 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.
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the processing of LC_MESSAGES
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:
The following exit values shall be returned:
- The utility executed successfully.
- An error occurred.
CONSEQUENCES OF ERRORS
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.
This first example tests the line counting option, comparing each
line of the input file data starting from the second
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).
The second example tests the option to suppress unique lines, comparing
each line of the input file data starting from the
uniq -d -f 1 uniq_0I.t #05 foo0 bar0 foo1 bar1
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
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.
COPYRIGHTPortions 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 .