use strict;
use warnings;
<<'COMMENT';
$foo = 'bar';
COMMENT
[download]

Will avoid the interpolation. But you will still get

Useless use of a constant in void context at temp.pl line 3.
[download]

To avoid that you can do:

use strict;
use warnings;
{
no warnings;
<<'COMMENT';
$foo = 'bar';
COMMENT
}
[download]

But that is a lot of work.