{
    my $x = 20;

    sub do_stuff {     
        print "$x \n"; 
    }

}

do_stuff();  #$x has gone out of scope here

--output:--
20           #…yet the sub can still see $x

##</code><code>##

use threads;
use threads::shared;


my $x = 20;

sub do_stuff{ 
    print "$x \n";    #closes over $x (as above)
}

threads->create(\&do_stuff)->join();

--output:--
20

##</code><code>##

use threads;
use threads::shared;

sub do_stuff{ 
    print "$x \n";   #doesn't close over $x
}

my $x = 20;         

threads->create(\&do_stuff)->join();   #perl copies $x to the thread
                                        

--output:--
<blank line>    #but the thread can't see $x