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my %seen; ... { ++$seen{$1}, pos($string) -= length($1) - 1 while $string =~ /(\w{ +$len})/g; }
---------------------------------------------------------------------- (?{$seen{$1}++}) run this block of Perl code ---------------------------------------------------------------------- (?!) fail ----------------------------------------------------------------------
(*FAIL) (*F) This pattern matches nothing and always fails. It can be used to force + the engine to backtrack. It is equivalent to (?!), but easier to rea +d. In fact, (?!) gets optimised into (*FAIL) internally.
$string =~ /(\w{2,})(?{$seen{$1}++})(?!)/;
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