Helge,

Here is a begining, this only parses the input data once. It could be more efficient, possibly the regexp could be turned into a split on /,\s*|\(/ and then a test made on the first part of the split, not sure what sort of data you are trying not to match but possibly something like this 

my ($test, $id, $key)=split /,\s*|\(/, $_, 4;
next unless $test=/PROBABLECAUSE\w*/;

[download]
You may want to fix keys starting with a cap so they match duplicates without. I put the processing in the loop reading STDIN, this was so I could test it easily by bashing a few lines in by hand. May also be a little more efficient as the script starts working as soon as it has its first line rather than waiting till all is in. 
#!/use/your/bin/perl -w
use strict;
my($line_count, @lines, %dup, @capkeys)=0;
while (<STDIN>) {
   if (m/PROBABLECAUSE\w*\((\d+),\s*\w*,\s+(\w*)/) {
      my ($id, $key)= ($1, $2);
      # check if any key has init caps (not allowed)
      if ($key =~ m/^[A-Z]\w*/) {
         push @capkeys, "$line_count: $id - $key\n";
         # you may want to fix up caps here before you store
         # the key so Keysomething matches keysomething
      }
      if (exists $dup{$key}) {
         print "Duplicates found\n";
         print "$dup{$key}->[0]: $dup{$key}->[1]\n";
         print "$line_count: $_\n";
      } else {
          $dup{$key}=[$line_count, $_]; # store line
      }
      $line_count++;
   }
}
print "keys with initial caps\n" if @capkeys;
foreach (@capkeys) {print}

[download]
update
Got my split sugestion a little wrong, field misscount should be
    my ($test, $id, undef, $key)=split /,\s*|\(/, $_, 5;
    next unless $test=/PROBABLECAUSE\w*/;

[download]
In the initial caps test is the \w* really required or would if ($key =~ m/^[A-Z]/ be OK ? What if the entire key is in upper case or will that never happen ?
cleaner code, now taking liberties !
Lets just fix those upper cased keys and not trouble the poor users.... 
#!/your/perl -w
use strict;
my($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++;
}

[download]

In reply to Re: I sense there is a simpler way... by Random_Walk
in thread I sense there is a simpler way... by HelgeG

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