uniq - Removes or lists repeated lines in a file
uniq [-cdu] [-f fields] [-s chars] [input-file [outputfile]]
Obsolescent Syntax [Toc] [Back]
uniq [-cdu] [-fields] [+chars] [input-file [output-file]]
The uniq command reads from the specified input_file, compares
adjacent lines, removes the second and succeeding
occurrences of a line, and writes to standard output.
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industry standards as follows:
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Precedes each output line with a count of the number of
times each line appears in the file. This option supersedes
the -d and -u options. Displays repeated lines
only. Ignores 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:
If the fields argument specifies more fields than
appear on an input line, a null string is used for
comparisons. Ignores the specified number of characters
when doing comparisons. The chars argument
is a positive decimal integer.
If specified with the -f option, the first chars
characters after the first fields fields are
ignored. If the chars argument specifies more
characters than remain on an input line, uniq uses
a null string for comparison. Displays unique
lines only. Equivalent to -f fields. (Obsolescent)
Equivalent to -s chars. (Obsolescent)
A pathname for the input file.
If this operand is omitted or specified as -, then
standard input is read. A pathname for the output
If this operand is omitted, then standard output is
The input_file and output_file arguments must be different
files. If the input_file operand is not specified, or if
it is -, uniq uses standard input.
Repeated lines must be on consecutive lines to be found.
You can arrange them with the sort command before processing.
To delete repeated lines in the following file called
fruit and save it to a file named newfruit, enter: uniq
The file fruit contains the following lines:
apples apples bananas cherries cherries peaches pears
The file newfruit contains the following lines:
apples bananas cherries peaches pears
The following exit values are returned: Successful completion.
An error occurred.
ENVIRONMENT VARIABLES [Toc] [Back]
The following environment variables affect the execution
of uniq: Provides a default value for the internationalization
variables that are unset or null. If LANG is unset
or null, the corresponding value from the default locale
is used. If any of the internationalization variables
contain an invalid setting, the utility behaves as if none
of the variables had been defined. If set to a non-empty
string value, overrides the values of all the other internationalization
variables. Determines the locale for the
interpretation of sequences of bytes of text data as characters
(for example, single-byte as opposed to multibyte
characters in arguments). Determines the locale for the
format and contents of diagnostic messages written to
standard error. Determines the location of message catalogues
for the processing of LC_MESSAGES.
Commands: comm(1), sort(1)
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