in reply to regex for nested "<"/">'

I should like to thank all of you for your "help" -- I say "help" because you guys did all the real work!

What I am really after is getting a regex similar to Abigail's where "begin"/"end" must be complete words ie "\bbegin\b" and "\bend\b". Note that Abigail's will accept "beginning a bend".

To the Damian, I apologize for my poor transcription ... but I worked from screen shot and *+ was the best my poor 70 year old eyesight told me.

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Re^2: regex for nested "<"/">'
by jo37 (Curate) on Feb 12, 2020 at 21:42 UTC
    For balanced begin/end matching, this might do: 
    $re = qr{
        (
            (?:
                (?&OPEN)
                (?:
                    (?>(?:.*?(?=(?&OPEN)|(?&CLOSE))))
                    |
                    (?-1)
                )*
                (?&CLOSE)
            )
        )
        (?(DEFINE)
            (?<OPEN>\bBEGIN\b)
            (?<CLOSE>\bEND\b)
        )}x;

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      You're my hero!

      Now to figure out exactly how it works!

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Re^2: regex for nested "<"/">'
by tybalt89 (Monsignor) on Feb 13, 2020 at 17:00 UTC 
    #!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11112811
use warnings;

my $input = <<ENDOFSTRING;
beginning a bend
before stuff
begin
  one
  begin
    three
  end
  five
end
after stuff
beginning a bend
ENDOFSTRING

print $input, '-' x 70, "\n";

my $level = 0;
my $nested = $input =~ s/(\bbegin\b)|(\bend\b)|./
  ( $1 && $level++, $level ? $& : '', $2 && $level--)[1] /gesr;

print "$nested\n";

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    Outputs: 

    beginning a bend
before stuff
begin
  one
  begin
    three
  end
  five
end
after stuff
beginning a bend
----------------------------------------------------------------------
begin
  one
  begin
    three
  end
  five
end

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