Note the side-effect that "\" ceases to be special.

my $baz = 'interpolated';

print <<__EOI__;
Double quoted or unquoted
$baz
foo\\bar
__EOI__

print("\n");

print <<'__EOI__';
Single quoted
$baz
foo\\bar
__EOI__
[download]

Double quoted or unquoted
interpolated
foo\bar

Single quoted
$baz
foo\\bar
[download]