AFAIK the code between parens in the foreach statement is executed just once to obtain a list over which to iterate.
So yours is not really an optimization.
Update: i see now your and suaveant point as the inner loop get called multiple times: the original post was not that clear.

$|=$_='1g2i1u1l2i4e2n0k',map{print"\7",chop;select$,,$,,$,,$_/7}m{..}g

In reply to Re: Re: Finding all substrings by giulienk
in thread Finding all substrings by TheHobbit

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