Table 7-3. Logical Operators（表7-3 逻辑操作符）
example name result?/FONT>
$a and $b And True of both $a and $b are true.?/FONT>
$a or $b Or?/FONT> True if either $a or $b is true.?/FONT>
$a xor $b Or?/FONT> True if either $a or $b is true, but not both.?/FONT>
! $a Not?/FONT> True if $a is not true.?/FONT>
$a && $b And?/FONT> True of both $a and $b are true.?/FONT>
$a || $b Or?/FONT> True if either $a or $b is true.
两种不同“and”和“or”操作符的变化实际上是�