PHP language Quick Reference Guide

<?php
      //php code here
 ?>

• If the file just have PHP code, closing ?> can be skipped (recommended)
• // or # or /* ... */ are used for comments
• Each statement must be terminated with ;
• Short form of tags <?= ... ?> (returns and print the value) or <? ... ?> executes the PHP code;

1. Download php here.
2. Set the path of main installed folder (where there's 'php' executable e.g. php.exe on windows).
3. Run built-in server from cmd, from root of your code project:
   php -S localhost:8080
4. Accessing from browser, e.g: localhost:8080/Test.php
5. Use Notepad++ for editing php files or IDE like 'Eclipse for PHP Developers' which is free and has advance features like formatting, ref suggestions, PHP-CLI integration etc.

echo 'hello';

1. print: takes single string argument
2. printf: outputs the C style formatted string.
3. sprintf() function returns a formatted string instead of outputting.

<?php
$i = 3;
$j = 1.45;
$str = "Hi there!";
?>

• boolean
• integer
• float (double)
• string
• array e.g: $users = array("Steve", "Jenny");
• object e.g. $role = new Role('admin')
• null e.g. $a = null;
• resource e.g: $myDir = opendir('d:\test');

 $s = "Hey";
 echo '$s there.'; // $s there.
 echo "$s there."; // Hey there.
 echo "{$s}y there."; // Heyy there.

 echo "{$s} \"you\" there"//hey! "you" there

$s = "Hey";
echo <<<myLabel
$s,
How are "you" doing?
myLabel;

$s = "Hey";
echo <<<'myLabel'
$s,
How are "you" doing?
myLabel;

echo 'name = '.$name. ', email = '.$email;

<?php
$a = 'value a';
$b = 'value b';

//variable assignment by value
$b = $a;
$b = "new value of b";

echo "$a <br/>";
echo "$b <br/>";
?>

value a
new value of b

<?php
$a = 'value a';
$b = 'value b';

//variable assignment reference
$b = &$a; //prepend  &, this is the only change
$b = "new value of b";

echo "$a <br/>";
echo "$b <br/>";
?>

new value of b
new value of b

<?php
//defining function
function myFunctionName($myArg1, $myArg2,
                          $myArgWithDefault = true) {
     // apply some code logic
    return "$myArg1, $myArg2 , $myArgWithDefault";
}

//calling function
echo myFunctionName('some value', 5);
?>

<?php
function someFunction(&$someArg) {
   $someArg = 10;
}

$aNumber = 4;
someFunction($aNumber);
echo $aNumber;
?>

<?php
function &someFunction() {
  static $val = 5;
  echo "value of val = $val <br>";
  return $val;
}

$var = &someFunction();
$var = $var + 4;
$var = someFunction();
?>

value of val = 5
value of val = 9 

  function myFunc(bool $myBool, int $myInt) {...}

Above types are loosely typed, that means an arg of string type can accept an int because an int is still convertible to string. But by declaring the script as strict_types=1 that cannot happen, i.e. it achieves strong typing:

<?php
  declare(strict_types=1);

  function myFunc(bool $myBool, int $myInt) {...}

  ...
?>

 function myFunc() : int {...}

<?php
function aFunction(... $vars){
    //better use foreach loop here
    echo "$vars[0], $vars[1], $vars[2]<br>";
}

aFunction("one", "two", "three");
?>

one, two, three

<?php
function aFunction(){
   $vars = func_get_args();
   echo "$vars[0], $vars[1], $vars[2]<br>";
}

aFunction("one", "two", "three");
?>

<?php
function aFunction($a, $b){
   echo "$a, $b<br>";
}

aFunction(...["one", "two"]);
?>

one, two

In above example we could have used variable arg syntax at both places, at function definition and at function call.

Function inside another function

A function can have any valid code including other functions and class definitions.

A function can also be defined conditionally (e.g. in if block).

 <?php
function aFunction(){
  echo "From a function<br/>";

  function aLocalFunction(){
    echo "From a local function</br>";
  }
}

aFunction();
aLocalFunction();
?>

From a function
From a local function

• Variables defined outside a function are 'global variables', a function cannot access them.
  
  
• Variable defined inside a function are 'local variables' and not accessible outside.
  
  
• Local variables defined with global keywords can use variables defined outside. Alternatively PHP special array $GLOBALS can be used to achieve the same. $GLOBALS is an associative array containing references to all variables which are defined in global scope of the script. This array also contain other super-global variables. $GLOBALS itself is super-global

<?php
$firstName = 'Steve';
$location = 'Alaska';
$zip = '11111';

function modifyUser() {
   echo "--- inside the function --- <br/>";
   $lastName = 'Willams';
   echo "firstName locally = $firstName <br/>";
   //using global keyword
   global $location;
   $location = 'Hawi';
   //alternative way to use global
   $GLOBALS['zip'] = '22222';
}

modifyUser();
echo "--- outside the function --- <br/>";
echo "firstName = $firstName <br/>";
echo "lastName = $lastName <br/>";
echo "location = $location <br/>";
echo "zip = $zip <br/>";
?>

--- inside the function ---
firstName locally =
--- outside the function ---
firstName = Steve
lastName =
location = Hawi
zip = 22222

<?php
function aFunction() {
  //static $result = getInitialValue(); this will cause syntax error
  static $result = 4;// initializes only once
  $result = $result +1;
  return $result;
}

function getInitialValue(){
  echo 'getInitialValue called';
  return 4;
}

echo aFunction().'<br/>';
echo aFunction().'<br/>';
echo aFunction().'<br/>';
?>

5
6
7

<?php
function aFunction($var){
   echo $var();
}

aFunction(function(){
 return "from a closure";
});
?>

<?php
function aFunction($var){
  echo $var();
}

$myFunc = function(){
  return "from a closure";
};

aFunction($myFunc);
?>

<?php
$myVar = 10;

function aFunction($var){
  echo $var();
}

$myFunc = function() use ($myVar){
  return "from a closure with global var = $myVar";
};

aFunction($myFunc);
?>

from a closure with global var = 10

<?php
function aFunction($var){
  echo "in the function var = $var <br>";
  return "theReturnedValue";
}

echo call_user_func('aFunction', 'somePassedVariable');
?>
 

Variable variables

<?php
$name = 'Mike';
$var = 'name';
echo $$var;
?> 

 Mike

Variable function

The built-in function is_callable() can be used to verify that a variable can be called as a function

<?php
function myFunction() {
   echo 'inside myFunction';
}

$var = "myFunction";
if (is_callable($var)) {
   $var();
}
?>

inside myFunction

Constants

Keyword const

Starting 5.3 we can also use the keyword const to define constants (it was only allowed within a class definition only before):
const XYZ = 'A constant value';
As opposed to 'define' they are compile time constants (just like static final variables in Java) that's why they cannot be inside a function but can be defined inside a class. The value assign must be a scalar value or scalar expression.

<?php
define ( "MAX_COUNT", 10 );

function myFunction() {
	if (defined("MAX_COUNT")) {
		echo MAX_COUNT;//same as echo constant("MAX_COUNT")
	}
}

myFunction ();
?>

<?php
const X = 2 * 3;
const Y = 'constant y value';
$var = 5;
//cont Z = $var does not work
echo X . '<br>';
echo Y;

Operators

Conditional statements

if (boolean-expression){
 //some code
}

<?php
if ($x > 5){
 echo 'x is greater than 5';
}
?>

<?php
$i = 0; //or even $i="0";

if ($i) {
  echo 'i is not zero';
} else {
  echo 'i is zero';
}
?>

if(boolean-expression){
 //some code
} else {
 //alternative code
}

<?php
if ($x > 5){
 echo 'x is greater than 5';
} else {
 echo 'x is less than 5';
}
?>

if(boolean-expression){
 //some code
} else if (boolean-expression2){
 //some other code
} else {
 /*this must get executed if all are false*/
 }

<?php
if ($x > 5){
 echo 'x is greater than 5';
} else if ($x < 0) {
 echo 'x is less than 5 and negative';
} else {
 echo 'x is between 0 and 5 inclusively';
}
 ?>

Other if/else syntax:

<?php if ($x > 5): ?>
 A is greater than 5
<?php endif; ?>

<?php
if ($a == 5):
echo "a equals 5";
echo "...";
elseif ($a == 6):
echo "a equals 6";
echo "!!!";
else:
echo "a is neither 5 nor 6";
endif;
?>

Ternary Operator

It is another conditional operator and is combination of ?and :

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, otherwise it evaluates to expr3. It can be nested as well:

<?php
$a = 9;
echo "The number $a is ".($a<6? 'less than': ($a==6? 'equal to': 'more than')).' 6';

switch Statement

switch is alternative way to write if/elseif/else blocks but it only works on discrete values specified with case keyword:

<?php
$x = 0;
switch ($x) {
case 5 :
echo "x equals 5";
break;
case 0 :
echo "x equals 10";
break;
default :
echo "value of x is $x";
}
?>
   

Loops

while (boolean expr){
statement
}

<?php
$a = 1;

while($a <= 5) {
 echo "value of a= $a <br>";
 $a++;
}
?>

do {
} while(boolean expr);

<?php
$a = 1;

do {
  echo "value of a = $a <br>";
  $a++;
} while ($a <=5);
?>

for (expr1; boolean expr2; expr3){
    statement
}

<?php
   for ($a = 1; $a <= 10; $a++) {
   echo "value of a = $a <br>";
}
?>

foreach (array_expression as $value){
    statement
}

<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as $value) {
  echo "array element: $value <br>";
}
?>

<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as $key => $value) {
  echo "array element: $key = $value <br>";
}
?>

 array element: 0 = 1
 array element: 1 = 2
 .....

<?php
$arr = array("Feb" => 28, "April" => 30);
foreach ( $arr as $key => $value ) {
   echo "array element: $key = $value <br>";
}
?>

array element: Feb = 28
array element: April = 30

Controlling loop

Using 'break' inside loops

The keyword 'break' ends execution of the current loop structure (that includes switch statement). An optional numeric argument e.g. 'break 2' specifies how many levels to be broken out (used inside nested loops), default is 1.

Using 'continue' inside loops

The keyword 'continue' is used to skip the rest of the current loop execution and continue with the next iteration. Just like 'break', 'continue' can also be used with an optional numeric value specifying how many level to be continues in case of various nested loops.

Arrays:

Arrays in php are ordered map.

They can be used as an array, collection, map etc.

An array can be multidimensional i.e. an array element can be other array.

Arrays are created by using array(..) construct or starting PHP 5.4 we can use [...].

Array functions:

count($anArray) to get array length.
is_array($aVar) finds whether a variables is an array.
array_key_exists('aKey', $anArray) Checks if the given key or index exists in the array.
Here's the complete list of array functions.

Indexed array

$x = ["Feb", "April"];
echo "$x[0] <br>";
echo "$x[1] <br>";

Feb
April

A map also known as associative array

$arr = ["name" => "Steve", "age" => 30];
foreach ( $arr as $key => $value ) {
	echo "array element: $key = $value <br>";
}

Multidimensional

$arr = ["name" => "Steve", "orders"=> [1,2,3]];

String functions and conversions:

PHP provides many built-in string function which includes trimming, accessing chars, splitting, joining, formatting, conversion to/from html entities, searching index, lower/upper case, sub-strings etc. A complete list of string functions is here.

Additionally, we can access string characters like an array e.g. $aString[1].

Other types can be converted to string by explicit casting or using strval() function. An integer or float can be converted to string and vice versa. The string conversion can be implicit depending on the context e.g. echo "a boolean $boolVar", if boolVar is true it will be converted to 1 otherwise to "" empty string.

$str = "Learning php";
echo substr($str, -3);

Output php

$arr = [1,3,5];
echo "$arr[2]";

5+ "2" will be 7 of type integer. Also this kind of conversion is allowed:

echo 5 + "6 apples";

Output: 11

$str = "this is one string";
foreach (str_split($str) as $v){
  echo $v. "<br>";
}

include/require statements

These functions allow to include other php, html or txt file within the current php file.

Difference between the two function is: require() produces fatal error, whereas, include produces warning.

The path specified can be relative or absolute. We can also use direname(__DIR__) which gives the absolute path of current dir to prepare the target file path.

If complete path is not specified but just file name e.g. include('fileName.php'), and php.ini (the main php configuration file) has 'include_path' specified then it's used to search the target file.

If a file contains a function, including it multiple time will cause error. Use include_once or require_once in that case.

<?php
function myFunction($var){
 echo "from myFunction $var";
}
?>

<?php
include 'includeTest.php';
myFunction("hi there!");
?>

from myFunction hi there!

Null checking

<?php
$var;
echo isset($var) ? 'value='.$var : 'not set';//not set
echo is_null($var) ? 'null' : 'not null';//null
echo $var == NULL? 'null': 'not null';//null
echo $var === NULL? 'null': 'not null';//null
echo $var?  'value='.$var : 'not a valid value';//not a valid value;

$var = null;
echo isset($var) ? 'value='.$var : 'not set';//not set
echo is_null($var) ? 'null' : 'not null';//null
echo $var == NULL? 'null': 'not null';//null
echo $var === NULL? 'null': 'not null';//null
echo $var?  'value='.$var : 'not a valid value';//not a valid value;

$var = '';
echo isset($var) ? 'value='.$var : 'not set';//value=
echo is_null($var) ? 'null' : 'not null';//not null
echo $var == NULL? 'null': 'not null';//null
echo $var === NULL? 'null': 'not null';//not null
echo $var?  'value='.$var : 'not a valid value';//not a valid value;

$var = 5;
echo isset($var) ? 'value='.$var : 'not set';//value=5
echo is_null($var) ? 'null' : 'not null';//not null
echo $var == NULL? 'null': 'not null';//not null
echo $var === NULL? 'null': 'not null';//not null
echo $var?  'value='.$var : 'not a valid value';//value=5;