perl -MO=Deparse -e ' $a = "foo"; $b = ''foo''; $c = q{foo}'  
$a = 'foo';
$b = 'foo';
$c = 'foo';

##</code><code>##

perl -MO=Deparse -e ' $a = "$foo"; $b = q{$foo};'  
$a = "$foo";
$b = '$foo';