Ah. PerlScript. :)

One problem is with your filename string:

my $sitelist_file="<c:\supportweb\content\sitelist.txt"
print $sitelist_file;
__END__
<c:supportwebntentsitelist.txt
[download]

Double-quoted strings treat backslash as starting escape sequences. Use single quotes instead:

my $sitelist_file='<c:\supportweb\content\sitelist.txt';
print $sitelist_file;
__END__
<c:\supportweb\content\sitelist.txt
[download]

A more fundamental problem is that you're not checking if your open succeeded. A standard check would have revealed this problem to you:

open DATA, $sitelist_file or die "Cannot open '$sitelist_file': '$!'";
[download]

... that is, if you know where to find the error log. It's been too long since I looked at ASP and PerlScript.

Oh, and you have a syntax error. Typo? for each should be foreach, or simply for:

for my $line (@lines){
  $response->write($line);
}
[download]

use strict;
use CGI::Pretty;
use Carp qw(croak);
my $sitelist_file='<c:\supportweb\content\sitelist.txt';
my $title = 'My Lines';
open my $data, '<', $sitelist_file
  or croak "No open on $sitelist_file";
my $text = do{local $/; <$data>};
close $data;
print header(),
      start_html({title=>$title});
foreach my $line (split "\n", $text){
  $response->write($line);
};
print end_html;
[download]

use strict;
use CGI::Pretty;
use Perl6::Slurp;
print header(),
      start_html(-title=>'My Lines');
foreach (split "\n", slurp '<c:\supportweb\content\sitelist.txt'){
  $response->write($_)}
print end_html;
[download]

  Content-Type: text/html; charset=ISO-8859-1
[download]

throop

hat-tip to Perl Best Practices

I'm betting that's ASP with PerlScript, not CGI.

Note the $response->write. Ah, nostalgia. :)

print "Just another Perl ${\(trickster and hacker)},"
The Sidhekin proves Sidhe did it!