use B::Deparse;

my $deparse = B::Deparse->new;

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

print $deparse->coderef2text($sub),"\n";
__END__
{
    my $filename = shift @_;
    return "/tmp/$x/" . $filename;
}