$a and $b    And    true if both $a and $b are true.
$a or $b    Or    true if either $a or $b is true.
$a xor $b    Xor    true if either $a or $b is true, but not both.
! $a    Not    true if $a is not true.
$a && $b    And    true if both $a and $b are true.
$a || $b    Or    true if either $a or $b is true.