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Ignore common line between 2 files in perl

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# 1  
Old 06-09-2013
Ignore common line between 2 files in perl
I want to ignore the same line which appear in File1 and File2 and then print the final result back in file1

File1
Code:
ABC
123
XYZ

File2
Code:
XYX

Output
Code:
ABC
123

I have to run this command on multiple servers over ssh.
Below is my code that worked only on same server and not over ssh.

Code:
 my $ignoredList = `cat File1 | grep -vf File2`;
           open ACTIVE, ">File1" or die "can't open 'File1': $!";
           print ACTIVE "$ignoredList";
           close (ACTIVE);

Last edited by Scrutinizer; 06-09-2013 at 05:12 AM.. Reason: code tags
# 2  
Old 06-09-2013
Why do you want to embed your shell commands in Perl to perform functionality that the Shell can easily provide itself? Try:
Code:
grep -vf File2 File1 > File3 && mv File3 File1

# 3  
Old 06-09-2013
If you want an exact line match, e.g. ABC should not match ABCD
Code:
fgrep -vxf File2 File1 > File3 && mv File3 File1

# 4  
Old 06-09-2013
With awk
Code:
awk 'FNR==NR {a[$0];next}  !($0 in a)'  File2 File1 > tmp
mv tmp File1

# 5  
Old 06-09-2013
The mv command requires write permission on the directory;
further it replaces a symbolic link by a file.
For an unknown environment (e.g. different OS types) one should replace mv by cp and rm
Code:
 ... > /tmp/File3.$$ &&
cp /tmp/File3.$$ File1
rm -f /tmp/File3.$$

BTW /tmp is not a safe place, and $$ is predictable.
Safer is mktemp
Code:
tmpfile=`mktemp` &&
 ... > $tmpfile &&
cp $tmpfile File1
rm -f $tmpfile

Last edited by MadeInGermany; 06-09-2013 at 11:36 AM..
# 6  
Old 06-09-2013
I don't see what the problem is with the mv command. There is however an issue with the previous awk command in the sense that it will not generate a return code and/or there is no test for success, so IMO that would need to be introduced .
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