if you don't want to do much programming: , you could try the following:

#!/usr/bin/perl -w

# literally, ALL this will do is show you whether the 
# string you're searching for is in both files. 
# you might want to know line numbers, too, but this won't
# do it without modification.

use strict;

# get variable, and filenames from wherever ...

if (in_file($pattern, $filename1) && in_file($pattern, $filename2) ) {
    print "Found $pattern in both $filename1 and $filename2\n";
} else {
    print "$pattern not found in both $filename1 and $filename2.\n";
}

sub in_file {
    my ($pattern, $filename) = @_;
    open FILE, $filename or die "Can't open $filename: $!\n";
    my $found =0;
    while (<FILE>) {
        # set found to a true value and exit the loop
        # if we find the pattern in the current line.
        $found=1, last if /$pattern/;
    }
    close FILE;
    $found;
}
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Of course, if you're on a *nix system, if (`/usr/bin/grep $pattern $filename1` && `/usr/bin/print grep $pattern $filename2`) {} could replace that whole sub, but then you have to worry about users putting in dumb patterns.

Philosophy can be made out of anything. Or less -- Jerry A. Fodor