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PHP Manual [Logical Operators]

PHP Manual || 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)

PHP Manual || Operators