#!/your/perl -w
use strict;
my($line_count, %dup)=0;
while (<STDIN>) {
    my ($test, $id, undef, $key)=split /,\s*|\(/, $_, 5;
    next unless $test=/PROBABLECAUSE\w*/;
    # If i may be so bold...
    $key = lc $key;
    if (exists $dup{$key}) {
        print "Duplicates found\n";
        print "$dup{$key}->[0]: $dup{$key}->[1]";
        print "$line_count: $_";
    } else {
        $dup{$key}=[$line_count, $_]; # store No and line
    }
    $line_count++;
}