Re^3: Regexes: finding ALL matches (including overlap)

[blokhead]

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 ;)