#!/usr/bin/perl

# https://perlmonks.org/?node_id=1221039

use strict;
use warnings;

my $someTTstring = <<END;
before
[% # this is a comment to the end of line
   foo = 'bar'
%]

<p>bw, bliako</p>

[%# placing the '#' immediately inside the directive
    tag comments out the entire directive
%]
[% outside %]
[%# placing the '#' immediately inside the directive
    tag comments out the entire directive
    [% inside %]
%]
after
END

print stripcomments($someTTstring);

sub stripcomments
  {
  @_ and local $_ = shift;
  my $answer = '';
  $answer .=
    /\G\[\%#/gc ? stripcomments() x 0 :
    /\G\[\%/gc ? '[%' . stripcomments() =~ s/#.*//gr . '%]' :
    /\G\%\]/gc ? return $answer :
    /\G./gcs ? $& :
    return $answer while 1;
  }