if($this && $that) { 
some code here
}
unless($this || !$the_other) { 
some code here
}

Some older code would occasionally use these operators for shortcuts, but Perl 5 now has low precedence operators specifically for that purpose.
The && and || operators have the special property of returning the last value evaluated, instead of 1 for truth. That allows the following to work:

$x = shift || "default";

If the shift operator doesn't return a value, the "default" value will be assigned to $x instead.