Use HTML::Parser like so.

#!/usr/bin/perl -w
use strict;
use HTML::Parser;

my $p = HTML::Parser->new(    
        start_h => [\&Start, 'tagname, attr, text '],
        end_h => [sub { print  shift;  }, 'text'],
        comment_h => [sub { print  shift;  }, 'text'],
        default_h => [sub { print  shift;  }, 'text'],
    );
    
    open (IN, "<form.template") or die "Couldn't open!:$!";    # Your 
+html
    my $content = '';
    {
    local $/=undef;
    $content = <IN>;

    }

    $p->parse($content);

    close(IN) or die "Couldn't close:$!";

################################################
sub Start{ 
    my ($tag, $attr,$text) = @_; 
    

    if ($tag eq 'mytag'){
        $text = "WHATEVER YOU WANT TO REPLACE HERE.
    }

    print $text;


}
[download]

---

Update
Just FYI, $attr in start is a hashref with keys that are the lc attributes of the tag and values which are, the values.

-Lee

"To be civilized is to deny one's nature."