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Linux command  'comm' and whitespace

Posted on 2014-11-20
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Last Modified: 2014-11-22
I am seeing every single line show up on my comm comparison, because one file uses spaces, while the other uses tabs

Is there any way to get comm to print out the differences that exclude white space ?

Thanks
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Question by:Anthony Lucia
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by:woolmilkporc
ID: 40455791
Alas, "comm" does not have such an option.

"diff" on the other hand, does have options for this, "-w" to ignore all whitespace and "-b" to ignore changes in the number of whitespaces.

diff -w a.conf b.conf

If you don't want to see the additional info which "diff" provides but only the changes:

diff -w a.conf b.conf | grep -E "^<|^>"

If you don't want to see the additional info which "diff" provides and finally filter out the "<" and ">" characters:

diff -w a.conf b.conf | grep "^<" | cut -f2- -d" "
(differences in file 1)

diff -w a.conf b.conf | grep "^>" | cut -f2- -d" "
(differences in file 2)

diff -w a.conf b.conf | grep -E "^<|^>" | cut -f2- -d" "
(all differences)
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woolmilkporc earned 500 total points
ID: 40455804
To work with "comm" nevertheless you could delete all whitespace before comparing:

sort b.conf | tr -d " \t" > b.conf.sorted
sort a.conf | tr -d " \t" | comm -2 -3 - b.conf.sorted
rm b.conf.sorted

Instead of " \t" you can use the "[:blank:]" character class.

The drawback with all of the above is that the final output will also lack the whitespaces.
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