The code

    print APPEND $line2
         if $line2 =~ /$line1/;
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is not a good way to look for an IP address in a line of text. First of all, it will match when you're searching for an IP that's a substring of the one contained in the text:

    $line1 = '1.2.3.4';
    $line2 = '111.2.3.44';
    print "match\n" if $line2 =~ /$line1/;
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Second, the periods in IP address strings will be interpreted as regular expression metacharacters:

    $line1 = '1.2.3.4';
    $line2 = '11223344';
    print "match\n" if $line2 =~ /$line1/;
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