my %path;
$path{$_}=$path{$_} || 1 + keys %path for split /$sep/,$path;
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there are other more efficient ways to do that btw, im just feeling moderately cheeky. ;-)

And for the curious you cant write that as ||= because of a bug in Perl (on some versions of Perl anyway).

Update:

Or maybe its not a bug. According to some the docs should be read to say that it should be valid to say

my %path;
$path{$_}||=keys %path for split /$sep/,$path;
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and some are saying that the results are undefined. sigh