uniq(1) — Commands
NAME
uniq − Removes or lists repeated lines in a file
SYNOPSIS
Current Syntax
uniq [−cdu] [-f fields] [-s chars] [input-file [output-file]]
Obsolescent Syntax
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.
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
uniq: XPG4, XPG4−UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
FLAGS
-cPrecedes each output line with a count of the number of times each line appears in the file. This flag supersedes the -d and -u flags.
-dDisplays repeated lines only.
-f fieldsIgnores 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 argument specifies more fields than appear on an input line, a null string is used for comparisons.
-s charsIgnores the specified number of characters when doing comparisons. The chars argument is a positive decimal integer.
If specified with the -f flag, 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.
-uDisplays unique lines only.
-fieldsEquivalent to -f fields. (Obsolescent)
+charsEquivalent to -s chars. (Obsolescent)
PARAMETERS
input_fileA pathname for the input file.
If this parameter is omitted or specified as -, then standard input is read.
output_fileA pathname for the output file.
If this parameter is omitted, then standard output is written.
DESCRIPTION
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.
ENVIRONMENT VARIABLES
The following environment variables affect the execution of uniq:
LANGProvides 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.
LC_ALLIf set to a non-empty string value, overrides the values of all the other internationalization variables.
LC_CTYPEDetermines 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).
LC_MESSAGESDetermines the locale for the format and contents of diagnostic messages written to standard error.
NLSPATHDetermines the location of message catalogues for the processing of LC_MESSAGES.
EXAMPLES
To delete repeated lines in the following file called fruit and save it to a file named newfruit, enter:
uniq fruit newfruit
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
EXIT VALUES
The following exit values are returned:
0Successful completion
>0An error occurred