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Full Discussion: help on COMM command please
Top Forums UNIX for Dummies Questions & Answers help on COMM command please Post 302435895 by methyl on Thursday 8th of July 2010 01:05:53 PM
Old 07-08-2010
It is important to remember that "comm" assumes that both files are sorted.

Using two sorted test data files file1.txt and file2.txt.
Code:
cat file1.txt 
line 1
line 2
line 3
line 4
line 5

cat file2.txt
line 1
line 3
line 5
line 7

Code:
comm file1.txt file2.txt
                line 1
line 2
                line 3
line 4
                line 5
        line 7

Column 1 contains records only in file1.txt.
Column 2 contains records only in file2.txt
Column 3 contains records common to both files.

Code:
Now: comm -12 removes columns 1 and 2 - leaving only column 3 (lines common to both files).
comm -12 file1.txt file2.txt
line 1
line 3
line 5

Code:
Now: comm -3 removes column 3 - leaving columns 1 and 2 
comm -3 file1.txt file2.txt
line 2
line 4
        line 7

This User Gave Thanks to methyl For This Post:
 

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COMM(1) 						    BSD General Commands Manual 						   COMM(1)

NAME
comm -- select or reject lines common to two files SYNOPSIS
comm [-123f] file1 file2 DESCRIPTION
The comm utility reads file1 and file2, which should be sorted lexically, and produces three text columns as output: lines only in file1; lines only in file2; and lines in both files. The filename ``-'' means the standard input. The following options are available: -1 Suppress printing of column 1. -2 Suppress printing of column 2. -3 Suppress printing of column 3. -f Fold case in line comparisons. Each column will have a number of tab characters prepended to it equal to the number of lower numbered columns that are being printed. For example, if column number two is being suppressed, lines printed in column number one will not have any tabs preceding them, and lines printed in column number three will have one. comm assumes that the files are lexically sorted; all characters participate in line comparisons. EXIT STATUS
comm exits 0 on success, >0 if an error occurred. SEE ALSO
cmp(1), diff(1), sort(1), uniq(1) STANDARDS
The comm utility conforms to IEEE Std 1003.2-1992 (``POSIX.2''). BSD
June 6, 1993 BSD
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