4. Operators

Operators are used with one or more values (or expressions) which yields another value (so that the operator itself becomes an expression). Expressions can be combinations of operators, functions and variables. Below are the available operator types described. Note that operators are always part of expressions. If no parentheses are used when combining multiple operators within a statement, the expression is resolved from left to right. Therefore, the expression 2 + 2 . "test" will return "4test". The exception is multiplication, division and modulus, which has higher priority than plus and minus.

4.1. Assignment

Assignments will store the value of the expression to the right of the equal sign (=) in a variable to the left. An expression consisting of an assignment will have the value that was assigned. This is useful when assigning a variables in e.g. if statements.

$var = 42;
if (($random = rand(0, 9)) > 5) echo "$random is larger than 5";

4.1.1. Augmented assignment

Augmented assignment operators are documented in the arithmetic chapter.

$var = 5;
$var = $var + 5; // 10

$var = 5;
$var += 5; // 10


Assignments which could be written as augmented assignments are automatically optimized as such by the compiler.


An assignment to “self” (the same variable) on the right side of an augmented assignment yields “undefined” behavior and should not be relied upon.

$var = 5;
$var += ($var = 10);

4.1.2. Destructuring assignment

Destructuring assignment assigns variables with values taken from an array value. If the value is not an array, all variables will be assigned null or its default value.

[$a, $b, $c = 3] = [1, 2];
echo $a; // 1
echo $b; // 2
echo $c; // 3 // default value

Keyed index assignments are also supported.

        "result" => $result = [],
        "error" => $error = 0,
        "dnssec" => $dnssec = false
] = dns("halon.io", ["extended_result" => true]);

It’s however not possible to mix keyed with unkeyed assignments.


If there is less variables in the assignment list than array values, the remaining values will be discarded.

[$a] = [0, 1, 2];

If there is more variables in the assignment list than array values, the remaining variables will be assigned the value of none or its default value.

[$a, $b = 1, $c = 2] = [0];

4.2. Arithmetic

These are the arithmetic operators supported, most of which operates on numbers. The operator associativity follow the rules of most languages (e.g. C); explicit parentheses may be added to change or clarify the expression.

$var = (3 - 2) + 2;
  Operator Augmented assignment Augmented assignment expansion
Addition + += x = x + y
Subtraction - -= x = x - y
Multiplication * *= x = x * y
Division / /= x = x / y
Modulus % %= x = x % y
Exponentiation ** **= x = x ** y
Concatenation . .= x = x . y
Precedence Operator Associativity
1 . Left to right
2 + - Left to right
3 * / % Left to right
4 ** Right to left


HSL has constant folding, so numeric calculations are done at compile-time. Which means that 3600 * 24 is just as fast as using the constant 86400.


The ** operator should be used for performance instead of the pow() function.

4.3. String

Strings support the subscript and slicing operator documented in the array section.

4.3.1. Concatenation

It’s possible to use the . concatenation operator on any data type (except None), in which case both operands will be casted to a string.

echo "Hello " . "World";
echo "A number " . 5.5;
echo 1.0 . 2.5; // "12.5"

4.4. Array

4.4.1. Subscript

Single items in arrays can be accessed using the subscript ([]) operator. This operator may be used on variables, literals or functions.

If reading and the index doesn’t exist, None is returned.

$var = ["bar", "bar"];
echo $var[2]; // not found none is returned

If assigning to a variable and the index is not found, the variable is converted to an array and the item is created.

$var = [];
$var[2] = "baz";
echo $var[2]; // "baz"

If assigning to a variable and the subscript operator is empty [], the item will be appended to the array (the variable is converted to an empty array first if needed).

$var = [];
$var[] = "baz";
echo $var[0]; // "baz"

Numeric indexes are zero based. If the indexing is sequential (starting from zero) the array allows for direct access (random access) where reads and stores are done in constant O(1) time.

| H | a | l | o | n |
  0   1   2   3   4

It’s possible to chain the index operator with the [:] slicing operator.

The following key casting rules apply.

  • Strings (“1”) containing integers are casted to numbers (1).
  • Numbers (1.10) are casted to integers (1) ignoring the decimal part (x.10). 32bit signed integers are used.
  • All other values are matched as-is.
echo ["1"=>123]; // [1=>123]
echo [1.9=>123]; // [1=>123]
echo ["1.9"=>123]; // ["1.9"=>123]


Use the isset() function to check if a key (index) exists in an array.

4.4.2. Slicing

Slicing is done using the [first:last] operator. The indexes of each side of the : may be omitted, first index default to 0, and last index default to the length of the input, thus [:] will return a copy of the inputs values but the keys will re-indexed (numerically). The first index is inclusive and the last index is exclusive. Negative indexes are supported. If indexes causes out-of-bound, an empty type (array or string) is returned. The slicing operator works the same on arrays and strings. Indexes are counted as if the input was iterated; thus associative arrays have no special meaning.

 | H | a | l | o | n |
 0   1   2   3   4   5
-5  -4  -3  -2  -1
$test = "Halon";
echo $test[:]; // Halon
echo $test[1:4]; // alo
echo $test[-1:]; // n
echo $test[-3:]; // lon
echo $test[-5:-2]; // Hal
echo $test[:2] . $test[2:]; // Halon

4.4.3. Push and pop

Operation HSL PHP
shift $array = $array[1:]; array_shift($array);
unshift $array = [“item”] + $array; array_unshift($array, “item”);
pop $array = $array[:-1]; array_pop($array);
push $array = $array + [“item”]; array_push($array, “item”);
push $array = $array + “item”; array_push($array, “item”);
push $array[] = “item”; array_push($array, “item”);

When adding two arrays together, associative keys will be merged (the first array’s data will overwritten where keys conflict) and numeric indexes will be incremented (regardless if they conflict or not).

4.4.4. Removing

In order to remove specific value(s) from an array (and if push and pop is not appropriate) use the subtraction (-) operator to remove based on value (all value matched will be removed) and unset() to remove based on a specific key (index). The subtraction operator supports both single items and arrays (where all values will be removed). The array will not be re-indexed (for that use the slice operator ($var = $var[:]).

echo ["foo", 5] - 5; // [0=>"foo"]
echo ["foo", "foo", 5] - "foo"; // [2=>5]
echo ["foo", 5] - ["foo", 5]; // []


Use the unset() function to unset values based on the key (index).

4.5. Logic (boolean)

Logic operators treats all expressions and variables as either true or false. The truthiness depends on the data type.

Test Operator Descriptions
and and And operator
or or Or operator
not not Not operator
not ! Not operator

4.5.1. Short-circuit evaluation

The and and or operations are short-circuit. They will only evaluate the right statement if the left one doesn’t satisfy the condition. In the example below, bar() is not executed because foo() return true, thus satisfying the condition.

function foo() { return true; }
function bar() { return false; }

if (foo() or bar()) echo "foo or bar";

4.6. Bitwise

Bitwise operators treat their operands as 32 bits signed integers in two’s complement format. The result of these operators are regular numbers.

Test Operator Descriptions
and & Bitwise AND operator
or | Bitwise OR operator
xor ^ Bitwise XOR operator
not ~ Bitwise NOT operator
<< << Shift left, padded with zeros
>> >> Shift right, sign-propagating
$flags = 5;

$flagA = 0b0001;
$flagB = 0b0010;
$flagC = 0b0100;
$flagD = 0b1000;
if ($flags & ($flagB | $flagC)) echo "match";

4.7. Comparison

These operators compare the expressions (operands) on both sides of the operator with one another, and the expression return either true or false if they matched.

Test   Description Works on types
equality == Matches for equality Any
inequality != Matches for inequality Any
less than < Matches for less than Numbers
greater than > Matches for greater than Numbers
less or equal than <= Matches for less than Numbers
greater or equal than >= Matches for greater than Numbers
regular expression =~ Matches for equality using regular expressions Strings
inequality regular expression !~ Matches for inequality using regular expressions Strings


If comparing two operands of different data type, the result may be “unexpected”, therefore always explicitly convert them if needed using functions like number() and string().

4.7.1. Regular expression

The regular expression operator (=~ and not-match !~ operator) matches a string by default using partial matching. That means it allows a substring to match. To explicit mark the beginning or end of a pattern, use ^ for beginning and $ for the end. The regular expression implementation is “Perl Compatible” (hence the function names pcre_...), for syntax see the perlre documentation. The following modifiers are supported.

if ($var =~ ''\bhalon\b'') echo "contain the word halon";


If using raw strings with regular expressions there is no need to escape some characters twice. Literal strings (both double-quoted (without variable interpolation) and raw strings) as regular expressions will be precompiled for greater performance.

See also

For data extraction using regular expressions see pcre_match() family of functions. Pattern modifiers

Use pattern modifiers to change the behavior of the pattern engine, they have the capability to make the match case-insensitive and activate UTF-8 support (where one UTF-8 characters may be matched using only one dot) etc. They are activated by encapsulate the pattern using the /regular_expression/modifiers syntax. The regular_expression part should be a regular expression, and the modifiers should be zero or many of.

Modifier Internal define Description
i PCRE_CASELESS Do case-insensitive matching
m PCRE_MULTILINE See perl documentation
u PCRE_UTF8 Enable UTF-8 support
s PCRE_DOTALL See perl documentation
x PCRE_EXTENDED See perl documentation
U PCRE_UNGREEDY See perl documentation
X PCRE_EXTRA See perl documentation


It’s not necessary to encapsulate regular expressions with // unless modifiers are used.

4.8. Function

4.8.1. Call

Functions may be called using the () operator. It applies to both regular functions as well as anonymous functions and named function pointers.

$multiply = function ($x, $y) { return $x * $y };
echo $multiply(3, 5); // 5

4.8.2. Property

The property operator may be used to call functions on objects (arrays). It acts the same as the subscript operator ([]) but only supports function calling ().

function makeCounter() {
        $n = 0;
        return [
                "inc" => function () closure ($n) { $n += 1; },
                "get" => function () closure ($n) { return $n; },
$counter1 = makeCounter();

$counter1["inc"](); // 2
$counter1->inc();   // 1