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Top Forums Shell Programming and Scripting bash keep only duplicate lines in file Post 302653573 by agama on Saturday 9th of June 2012 01:57:02 PM
Old 06-09-2012
To do this a bit more information is needed:

1) is the file sorted, or are the lines you wish to 'keep' adjacent to each other in the file?

2) is the order of the output important? Do the lines 'kept' need to be in the same order that they appeared in the input?

3) do some lines appear more than twice, and should those be kept as well, or do you want to keep the lines that appear exactly twice?

4) how big is the file in terms of number of lines?

Last edited by agama; 06-09-2012 at 02:57 PM.. Reason: typo
 

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COMM(1) 							   User Commands							   COMM(1)

NAME
comm - compare two sorted files line by line SYNOPSIS
comm [OPTION]... FILE1 FILE2 DESCRIPTION
Compare sorted files FILE1 and FILE2 line by line. With no options, produce three-column output. Column one contains lines unique to FILE1, column two contains lines unique to FILE2, and column three contains lines common to both files. -1 suppress column 1 (lines unique to FILE1) -2 suppress column 2 (lines unique to FILE2) -3 suppress column 3 (lines that appear in both files) --check-order check that the input is correctly sorted, even if all input lines are pairable --nocheck-order do not check that the input is correctly sorted --output-delimiter=STR separate columns with STR --help display this help and exit --version output version information and exit Note, comparisons honor the rules specified by 'LC_COLLATE'. EXAMPLES
comm -12 file1 file2 Print only lines present in both file1 and file2. comm -3 file1 file2 Print lines in file1 not in file2, and vice versa. GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report comm translation bugs to <http://translationproject.org/team/> AUTHOR
Written by Richard M. Stallman and David MacKenzie. COPYRIGHT
Copyright (C) 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
join(1), uniq(1) The full documentation for comm is maintained as a Texinfo manual. If the info and comm programs are properly installed at your site, the command info coreutils 'comm invocation' should give you access to the complete manual. GNU coreutils 8.22 June 2014 COMM(1)
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