use Data::Dump::Streamer;

my $sub;
{
    my $x = "foo";
    $sub = sub {
        my $filename = shift;
        return "/tmp/$x/" . $filename;
    };
}

print Dump($sub);
__END__
my ($x);
$x = 'foo';
$CODE1 = sub {
           my $filename = shift @_;
           return "/tmp/$x/" . $filename;
         };