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Unix diff command to find the minus of two text files

Posted on 2014-03-17
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Last Modified: 2014-03-21
I want to print the content of file 1a that are not present in the file 1b. Both files contain one line of similar pattered text.
Example:
$ cat 1a
1234
3456
4567
$ cat 1b
1234
5566
9999
3456
$ grep -vf 1a 1b
5566
9999


$ grep -vf 1b 1a shows those present in 1a but not in 1b. And it works perfectly, But when the files are big (1000K+ records each), the above diff command hangs. Could you suggest workaround or alternate solution that might work? Thanks you.
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Question by:toooki
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5 Comments
 
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woolmilkporc earned 500 total points
ID: 39935760
You could use "comm". The drawback here is that both files must be sorted.

sort 1b > 1b.sort

sort 1a | comm -2 -3 - 1b.sort

will show the records present in file 1a but not in 1b(.sort)

I don't think that your grep command actually "hangs". Probably it just takes quite a long time to complete.
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Expert Comment

by:ozo
ID: 39935771
Your example seems to show a grep command, not a diff command.
If we can use other commands, this should work:
 perl -lne '@ARGV?$s{$_}++:$s{$_}||print' 1a 1b
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by:woolmilkporc
ID: 39935789
If you want to use "diff" then this one:

diff 1b 1a | grep "^>"

will show the lines of 1a which are not in 1b, preceeded by ">".

This one

diff 1a 1b |grep "^<"

will do the same, but the lines in question will be preceeded by "<".

This will remove the prefix:

diff 1a 1b |awk '/^</ {print $2}'
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Expert Comment

by:Gerwin Jansen, EE MVE
ID: 39938069
Off topic comment deleted.

Gerwin Jansen
EE Topic Advisor
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Author Comment

by:toooki
ID: 39946613
Many thanks to all.
sort 1b > 1b.sort
sort 1a | comm -2 -3 - 1b.sort

The above worked for me!
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