in reply to Getting data *INTO* __DATA_

This can be accomplished with a templating module, such as HTML::Template - 
use strict;
use HTML::Template;

my $name = 'Mr. Anderson';
my $data = do {local $/; <DATA>};
my $tmpl = HTML::Template->new(
   scalarref => \$data,
);

$tmpl->param(
   name => $name,
);

print $tmpl->output;

__DATA__
Content-type: text/html

<html><body>Hello <tmpl_var name>!</body></html>

[download]
I would use CGI qw(header); however, instead of hand-coding the header in __DATA__.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In Section Seekers of Perl Wisdom