Php/docs/language.operators.logical

PHP Manual
Operators
Logical Operators

Logical Operators

**Logical Operators**
Example	Name	Result
$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`.

The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See Operator Precedence.)

Example #1 Logical operators illustrated

<?php// --------------------// foo() will never get called as those operators are short-circuit$a = (false && foo());$b = (true || foo());$c = (false and foo());$d = (true or foo());// --------------------// "||" has a greater precedence than "or"// The result of the expression (false || true) is assigned to $e// Acts like: ($e = (false || true))$e = false || true;// The constant false is assigned to $f before the "or" operation occurs// Acts like: (($f = false) or true)$f = false or true;var_dump($e, $f);// --------------------// "&&" has a greater precedence than "and"// The result of the expression (true && false) is assigned to $g// Acts like: ($g = (true && false))$g = true && false;// The constant true is assigned to $h before the "and" operation occurs// Acts like: (($h = true) and false)$h = true and false;var_dump($g, $h);?>

The above example will output something similar to:

bool(true)
bool(false)
bool(false)
bool(true)