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You're right, use re 'eval' is not absolutely required, and I shouldn't have said it like that. But beware! Your example code works fine on just an instance-by-instance basis. But if you want to do this programatically and extensibly, then my warning about closure-ing lexicals applies. It's tricky to make a generic-use sub that does this kind of matching.

You may be tempted to do the following, but it won't work:

sub match_all_ways { my ($string, $regex) = @_; my $count; my $incr = qr/(?{$count++})/; $string =~ /(?:$regex)$incr(?!)/; return $count; } print match_all_ways("abcdef", qr/..*..*./); # 20 print match_all_ways("abcdef", qr/..*..*./); # undef
It's because the qr// object is compiled just once and always refers to the first instance of $count. If you call this sub more than once, you will always get undef.

You have to do something ugly like this to get around it:

sub match_all_ways { use vars '$count'; my ($string, $regex) = @_; local $count = 0; my $incr = qr/(?{$count++})/; $string =~ /(?:$regex)$incr(?!)/; return $count; }
or this
{ my $count; my $incr = qr/(?{$count++})/; sub match_all_ways { my ($string, $regex) = @_; $count = 0; $string =~ /(?:$regex)$incr(?!)/; return $count; } }
So yes, it can be done programatically without use re 'eval', but it's non-trivial and a little messy ;)


In reply to Re^3: Regexes: finding ALL matches (including overlap) by blokhead
in thread Regexes: finding ALL matches (including overlap) by kaif

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