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Top Forums Shell Programming and Scripting omitting lines from file A that are in file B Post 302168506 by earnstaf on Monday 18th of February 2008 03:39:17 PM
Old 02-18-2008
Quote:
Originally Posted by gneen
I've got file A with (say) 1M lines in it ... ascii text, space delimited ...

I've got file B with (say) 10M lines in it ... same structure.

I want to remove any lines from A that appear (identically) in B and print the remaining (say) 900K lines. (And I want to do it in zero time of course!)

Best I've come up with so far is somehow marking the lines in A, then doing a sort and applying an awk script to the result so that the marked lines are only printed if the following (or previous) line isn't "identical" except for the mark.

But after 1000 years of shell programming I've GOT to believe I'm missing an easier/faster solution ... I'm using bash and cygwin tools - and compiling is not an option.

ADVthanksANCE for your help!
=Gneen
Code:
cat fileA | while read line
do
grep -q "$line" fileB
if [ $? -eq 1 ]; then
echo "$line" > fileC
fi
done

Not sure how fast that would be, but fileC will end up with all the lines that were in fileA that were in not in fileB.
 

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uniq(1) 						      General Commands Manual							   uniq(1)

Name
       uniq - report repeated lines in a file

Syntax
       uniq [-udc[+n][-n]] [input[output]]

Description
       The  command  reads  the  input	file comparing adjacent lines.	In the normal case, the second and succeeding copies of repeated lines are
       removed; the remainder is written on the output file.  Note that repeated lines must be adjacent in order to be found.  For further  infor-
       mation, see

Options
       The n arguments specify skipping an initial portion of each line in the comparison:

       -n Skips specified number of fields.  A field is defined as a string of non-space, non-tab characters separated by tabs and spaces from its
	  neighbors.

       +n Skips specified number of characters in addition to fields.  Fields are skipped before characters.

       -c Displays number of repetitions, if any, for each line.

       -d Displays only lines that were repeated.

       -u Displays only unique (nonrepeated) lines.

       If the -u flag is used, just the lines that are not repeated in the original file are output.  The -d option specifies  that  one  copy	of
       just the repeated lines is to be written.  The normal mode output is the union of the -u and -d mode outputs.

       The  -c option supersedes -u and -d and generates an output report in default style but with each line preceded by a count of the number of
       times it occurred.

See Also
       comm(1), sort(1)

																	   uniq(1)
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