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Error Control Operators

When the at sign (@) is prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

If the track_errors feature is enabled, any error message generated by the expression will be saved in the variable $php_errormsg. This variable will be overwritten on each error, so check early if you want to use it.

<?php
/* Intentional file error */
$my_file = @file ('non_existent_file') or
die ("Failed opening file: error was '$php_errormsg'");
// this works for any expression, not just functions:
$value = @$cache[$key];
// will not issue a notice if the index $key doesn't exist.
?>

Note: The @-operator works only on expressions. A simple rule of thumb is: if you can take the value of something, you can prepend the @ operator to it.

For instance, you can prepend it to variables, function and include() calls, constants, and so forth. You cannot prepend it to function or class definitions, or conditional structures such as if and foreach, and so forth.

Execution operator

PHP supports one execution operator: backticks (``). Note that these are not single-quotes!

PHP will attempt to execute the contents of the backticks as a shell command; the output will be returned (i.e., it won't simply be dumped to output; it can be assigned to a variable). Use of the backtick operator is identical to shell_exec().

<?php
$output = `ls -al`;
echo "<pre>$output</pre>";
?>

Increment/decrement Operators

Example Name Effect
++$a Pre-increment Increments $a by one, then returns $a.
$a++ Post-increment Returns $a, then increments $a by one.
--$a Pre-decrement Decrements $a by one, then returns $a.
$a-- Post-decrement Returns $a, then decrements $a by one.

The increment/decrement operators do not affect boolean values. Decrementing NULL values has no effect too, but incrementing them results in 1.

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's.

For example, in Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 91 ). Note that character variables can be incremented but not decremented.

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.

Two different variations of "and" and "or" operators is that they operate at different precedences.

String Operators

There are two string operators:

  1. concatenation operator ('.'), which returns the concatenation of its right and left arguments.
  2. concatenating assignment operator ('.='), which appends the argument on the right side to the argument on the left side. Please read Assignment Operators for more information.

<?php
$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"
$a = "Hello ";
$a .= "World!"; // now $a contains "Hello World!"
?>

Array Operators

Example Name Result
$a + $b Union Union of $a and $b.
$a == $b Equality TRUE if $a and $b have the same key/value pairs.
$a === $b Identity TRUE if $a and $b have the same key/value pairs in the same order and of the same types.
$a != $b Inequality TRUE if $a is not equal to $b.
$a <> $b Inequality TRUE if $a is not equal to $b.
$a !== $b Non-identity TRUE if $a is not identical to $b.

The + operator appends the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

Elements of arrays are equal for the comparison if they have the same key and value.

Comparing arrays

<?php
$a = array("apple", "banana");
$b = array(1 => "banana", "0" => "apple");
var_dump($a == $b); // bool(true)
var_dump($a === $b); // bool(false)
?>

Type Operators

PHP has a single type operator: instanceof. instanceof is used to determine whether a given object is of a specified object class.

The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof.

<?php
class A { }
class B { }
$thing = new A;
if ($thing instanceof A) {
echo 'A';
}
if ($thing instanceof B) {
echo 'B';
}
?>

As $thing is an object of type A, but not B, only the block dependent on the A type will be executed:

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