Updated March 17, 2023
Introduction of PHP Keywords
Keywords are the words hold some meaning. In regular use of PHP language, these words cannot be used as a constant, a variable name, a method name, a class name, etc. These keywords when used are automatically understood by PHP. These PHP keywords, when used with variable names, can be confused with the actual keywords. Therefore, these keywords should not be used as variable names.
List of all PHP keywords
Following is a list:
Keyword: abstract
Code:
<?php
//example to demonstrate abstract keyword
abstract class Program {
abstract protected function MethodOne();
public function display() {
echo '<br>'.$this->MethodOne();
}
}
class ProgramOne extends Program {
protected function MethodOne() {
echo '<br>'.'In MethodOne';
}
}
$objOne = new ProgramOne;
$objOne->display();
?>,Output:
Keyword: and
Code :
<?php
//example to demonstrate and keyword
$a = 10;
$b = 11;
if($a ==10 and $b == 11) {
echo 'Result : True';
}
else
{
echo 'Result : False';
}
?>Output:
Keyword: array()
Code:
<?php
//example to demonstrate array keyword
$directions = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
print_r($directions);
?>Output:
Keyword: as
Code:
<?php
//example to demonstrate array keyword
$directions = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
foreach($directions as $key=>$value) {
echo '<br>'. $key. '=>'.$value;
}
?>Output:
Keyword: break
Code :
<?php
//use of break keyword without optional argument
$arr = array("water", "sky", "try", "sand");
foreach($arr as $key=>$value) {
if($value == 'try') {
break ; // can use break 1 also
}
echo '<br>'.$value;
}
?>Output:
Keyword: case
Code:
<?php
//example to demonstrate case keyword
$i = 1;
while($i<5) {
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
$i++;
}
?>Output:
Keyword: catch
Code:
<?php
//example to demonstrate catch keyword
function Operation()
{
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
die($e->getMessage());
}
}
Operation();
?>Output:
Keyword: class
Code:
<?php
//example to demonstrate class keyword
class ClassOne{
var $str = 'Hello World';
public function displayMethod() {
echo $this->str;
}
}
$obj = new ClassOne;
$obj->displayMethod();
?>Output:
Keyword: const
the const keyword is used to define the name with a value using assignment operator like below
const AGE= 29;
There is no $ sign at the beginning of a constant name like a normal variable has.
Keyword: default
Code:
<?php
// example to demonstrate default keyword
$fruits = 'Cherries';
switch ($fruits) {
case 'Apple':
echo "Apple";
break;
case 'Banana':
echo "Banana";
break;
case 'Papaya':
echo "Papaya";
break;
default:
echo "Fruit is not Apple, Banana or Papaya ";
break;
}
?>Output :
Keyword: do
Code:
<?php
// example to demonstrate do keyword
$x = 2;
do {
if($x > 2)
{
echo 'x is greater than 2';
}
else{
echo 'x is less than 2';
}
} while ($x < 2);
?>Output:
Keyword: die();
Code :
<?php
//example to demonstrate die keyword
$conn = mysqli_connect('localhost','root','','dbname');
if(!$conn) {
die("Unable to connect ");
}
?>Output:
Keyword: echo
Code:
<?php
// example to demonstrate echo keyword
echo 'Hello! ';
$name = 'John Doe';
echo 'My name is '. $name;
?>Output:
Keyword: else
Code:
<?php
// example to demonstrate else keyword
$a = 10;
if ($a > 5) {
echo "a is greater than 10";
} else {
echo "a is not greater than 10";
}
?>Output:
Keyword: elseif
Code:
<?php
// example to demonstrate elseif keyword
$a = 10;
if ($a > 10) {
echo "a is greater than 10";
} elseif ($a == 10) {
echo "a is equal to 10";
} else {
echo "a is smaller than 10";
}
?>Output :
Keyword: empty
Code:
<?php
// example to demonstrate empty keyword
$str = 'Hello World!';
if(empty($str)) {
echo 'Variable is empty';
} else {
echo $str;
}
?>Output:
Keyword: endfor
Code:
<?php
// example to demonstrate endfor keyword
for($i=0;$i<5;$i++) :
echo "<br/>".$i;
endfor;
?>Output:
Keyword: endif
Code :
<?php
// example to demonstrate endif keyword
if ($a > 10):
echo "a is greater than 10";
elseif ($a >10) :
echo "a is equal to 10";
else:
echo "a is not equal to 10";
endif;
?>Output:
Keyword: endforeach
Code:
<?php
// example to demonstrate endforeach keyword
$arr = array(1,2,3,4,5,6,7,8,9,10);
foreach ($arr as $key=>$value):
echo '<br>'.$value;
endforeach;
?>Output:
Keyword: endswitch
Code:
<?php
// example to demonstrate endswitch keyword
$fruits = 'Cherries';
switch ($fruits):
case 'Apple':
echo "Apple";
break;
case 'Banana':
echo "Banana";
break;
case 'Papaya':
echo "Papaya";
break;
default:
echo "Fruit is not Apple, Banana or Papaya ";
break;
endswitch;
?>Output:
Keyword: endwhile
Code:
<?php
// example to demonstrate endwhile keyword
$i = 0;
while($i<5):
echo "<br>".$i;
$i++;
endwhile;
?>Output:
Keyword: eval()
Code:
<?php
//example to demonstrate eval keyword
$string1 = 'World';
$string2 = 'John Doe';
$string = 'Hello $string1 . My name is $string2';
echo "<br>".$string;
eval("\$string = \"$string\";");
echo "<br>".$string;
?>Output:
Keyword: exit()
This keyword when encountered in a script, terminates the execution of the script.
Keyword: extends()
Code:
<?php
//example to demonstrate extends keyword
class ParentClass {
var $string = 'PHP';
public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>Output:
Keyword: final
Code:
<?php
//example to demonstrate final keyword
class ParentClass {
var $string = 'PHP';
final public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>Output :
Keyword: catch
Code:
<?php
//example to demonstrate catch keyword
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
?>Output:
Keyword: for
Code:
<?php
// example to demonstrate for keyword
for($i=0; $i<10; $i++) {
if($i == 5) {
break;
}
echo '<br>'.$i;
}
?>Output :
Keyword: foreach
Code:
<?php
// example to demonstrate foreach keyword
$array = array(10,20,30,40,50);
foreach($array as $value) {
echo '<br>'.$value/10;
}
?>Output:
Keyword: function()
Code:
<?php
function calSum($a , $b) {
$c = $a + $b;
return $c;
}
$result = calSum(10 , 20);
echo '<br> The sum : '.$result;
?>Output:
Keyword 34: global
Code:
<?php
//example to demonstrate global keyword
$a = 10;
$b = 20;
function fun() {
global $a;
global $b;
$result = $a + $b;
return $result;
}
$f = fun();
echo 'The result is '.$f;
?>Output:
Keyword: if
Code:
<?php
// example to demonstrate if keyword
$sum = 10;
if($sum == 10) {
echo 'Sum is 10';
} else {
echo 'Sum is not 10';
}
?>Output:
Keyword: implements
Code:
<?php
//example to demonstrate interface keyword
interface One
{
public function first();
}
class MainClass implements One {
public function first() {
echo 'This is the First function';
}
}
$obj = new MainClass;
echo $obj->first();
?>Output :
Keyword: include
Code:
file.php
<?php
//example to demonstrate include keyword
$a = 'The Earth';
$b = 'Round';
?>index.php
<?php
include 'file.php';
echo $a . ' is '. $b. ' in Shape';
?>Keyword : include_once
Code:
file.php
<?php
//example to demonstrate include_once keyword
$a = 'The Earth';
$b = 'Round';
?>index.php
<?php
Include_once 'file.php';
echo $a . ' is '. $b. ' in Shape';
?>Output:
Keyword: instanceOf
Code:
<?php
//example to demonstrate instanceOf keyword
class MainClass
{
public function MainCLassMethod(){
echo 'Hello World!';
}
}
class ExtendedClass extends MainClass
{
public function ExtendedClassMethod(){
echo 'Have a Nice Day!';
}
}
$obj1 = new ExtendedClass;
var_dump($obj1 instanceOf ExtendedClass);
?>Output:
Keyword: Interface
Code:
<?php
//example to demonstrate interface keyword
interface One
{
public function one();
}
interface Two
{
public function two();
}
class MainClass implements One, Two {
public function one() {
echo '<br> This is the one function';
}
public function two() {
echo '<br> This is the two function';
}
}
$obj = new MainClass;
echo $obj->one();
echo $obj->two();
?>Output:
Keyword: isset
Code:
<?php
//example to demonstrate isset keyword
$stringOne = '';
var_dump(isset($stringOne));
$stringTwo = NULL;
var_dump(isset($stringTwo));
?>Output :
Keyword: list
Code:
<?php
//example to demonstrate list keyword
$names = array('Ram','Mohan','Raghav');
list($person1, $person2, $person3) = $names;
echo "$person1, $person2 and $person3 are friends";
?>Output:
Keyword: new
Code:
<?php
//example to demonstrate new keyword
class Student
{
public function score($name, $subject, $marks) {
echo "$name scored $marks marks in $subject";
}
}
$obj = new Student;
$obj->score('Sunil','Maths',90);
?>Output:
Keyword: or
Code:
<?php
//example to demonstrate or keyword
$a = 10;
$b = 11;
if($a ==10 or $b == 12) {
echo 'Result : True';
}
else
{
echo 'Result : False';
}
?>Output :
Keyword: print
Code:
<?php
//example to demonstrate print keyword
$str = "PHP Programming";
print($str);
$stringOne = "Shyam, ";
$stringTwo = "How are you?";
print "<br>"."Hello $stringOne $stringTwo";
?>Output :
Keyword: private
Code:
<?php
//example to demonstrate private keyword
class MainClass
{
private $str = 'Private';
function PrivateMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PrivateMethod(); //Shows Private Method
?>Output:
Keyword: public
Code:
<?php
//example to demonstrate public keyword
class MainClass
{
public $str = 'Public';
function PublicMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PublicMethod(); //Shows Public Method
?>Output:
Keyword: protected
Code:
<?php
//example to demonstrate protected keyword
class MainClass
{
protected $str = 'Protected';
function ProtectedMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->ProtectedMethod(); //Shows Protected Method
?>Output:
Keyword: return
Code:
<?php
//example to demonstrate return keyword
function sum() {
$a = 10;
$b = 20;
$c = $a +$b;
return $c;
}
$result = sum();
echo 'Sum : ' . $result;
?>Output:
Keyword: switch
Code:
<?php
//example to demonstrate switch keyword
$i= 3;
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
?>Output:
Keyword: throw
Code:
<?php
//example to demonstrate throw keyword
function division($x, $y) {
try {
if($y == 0) {
throw new Exception('Divide By Zero');
}
}
catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
}
division(10,0);
?>Output:
Keyword: Try
Code:
<?php
//example to demonstrate try keyword
try{
$arr = array();
$arr_length = count($arr);
if($arr_length == 0) {
throw new Exception('Error : Empty Array!');
}
else {
echo 'Array found';
print_r($arr);
}
}
catch(Exception $e) {
echo '<br>'.$e->getMessage();
}
?>Output:
Keyword: unset
Code:
<?php
//example to demonstrate unset keyword
echo 'Hello World!'.'<br>';
$a = 10;
echo $a;
unset($a);
// echo $a; //this line when uncommented shows error : Undefined variable, as the variable is unset
?>Output:
Keyword: var
Code:
<?php
//example to demonstrate var keyword
class MainClass
{
var $str = 'PHP Programming';
public function displayMsg() {
echo $this->str;
}
}
$obj = new MainClass;
$obj->displayMsg();
?>Output:
Keyword: while
Code:
<?php
//example to demonstrate while keyword
$i = 0;
while ($i<10) {
echo '<br>'. $i;
$i++;
}
?>Output:
Conclusion
In this article, you will learn about keywords in PHP with examples. These examples explain the usage of each of the keyword in PHP.
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