$a || $b # logical or: true if either is nonzero 
$a && $b # logical and: true only if both are nonzero 
! $a # logical not: true if $a is zero 
Perl 5 also defines these logical operators: 
$a or $b # another form of logical or 
$a and $b # another form of logical and 
not $a # another form of logical not 
$a xor $b # logical xor: true if either $a or $b is nonzero, but not both