PHP

PHP is a language that is embedded within an HTML file. It doesn't have to be within an HTML document, though.

Syntax

PHP code must be enclosed within special tags: <?php and ?>

<?php
  $hello = "Hello"
  $world = "world"
  // Say hello
  echo "${hello}, " . "${world}!";
?>

Variables

Variables are prefaced by a $.

$x = 4;
$y = "Yeah";
$z = True;

String formatting can be performed as it is in shell scripts, by using double quotes.

$name = "John";
$greeting = "Hello, $name";

Function

Functions are defined similar to Javascript:

function example($arg1, $arg2 = "Yeah") {
  echo "Yay";
  return 1;
}

example("1");
example("1", "2");

// Anonymous function;

$add = function($num1, $num2) {
  return $num1 + $num2;
}

$add(5, 5);

$sub = fn($num1, $num2) => $num1 - $num2;

$sub(5, 5);

Scope

Functions create a scope where variables defined within are only accessible within, but also that variables defined outside of the scope are not readily accessible. To access a globally scoped variable, the variable must be introduced with a global call.

$outside = "test";

function example() {
  // echo $outside;  This will error out
  global $outside;
  echo $outside;

  $inside = "We are no longer " . $outside;

  return 1;
}

// echo $inside;  This will error out

Super Globals[3]

Super globals are variables that are available at all levels. These include syste information, request information, cookies, etc.

Data Types

• String: single or double quotes
• Integer
• Float
• Boolean
• Array
• Objects
• null
• Resource

String Methods

Strings can be concatenated using ..

$str = "Hello, " . "World!";
$str .= " Good afternoon, good evening, and goodnight.";

htmlspecialchars(str) will escape all HTML characters in a string, making you safer from script injections.

Alternatively, if the input string is a cookie, GET value, etc., you can use filter_input[4], which has special rules and helper variables.

Arrays

$numbers = [1,2,3,4];
// or
$numbers = array(1,2,3,4);

$first_item = $numbers[0];

Associative arrays are like Javascript objects or Python dictionaries.

$people = {
  "john" => 55,
  "jane" => 19,
  "bob" => 11,
  "jill" => 92
};

$john_age = $people["john"];

Methods

Conditionals

Conditionals are written the same way as Javascript, in terms of if blocks, except elseif is together instead of separated. Ternary statements and switch cases are the same as well.

Like Javascript, PHP has double- and triple-equals for testing equality; double is for testing equal in value, triple is for testing identical in value and type.

Conditional HTML

PHP can render HTML conditionally without resorting to running echo everywhere.

<?php if ($loggedIn) { ?>
  <h1>You are logged in!</h1>
  <p>Any valid HTML will be conditionally rendered</p>
<?php } else if ($var === 1) { ?>
  <p>Something else</p>
<?php } else { ?>
  <p>Last thing</p>
<?php } ?>

Loops

For loops, while loops, and do while loops are the same as Javascript.

The foreach loop is unique to PHP in that it is similar to Javascript's .forEach method on iterables, but is a statement that takes in an array or associative array as an expression:

$posts = ["title1", "title2", "title3"];

foreach ($posts as $post) {
  echo $post;
}

$posts = {
  "title1" => "Content1",
  "title2" => "Content2",
  "title3" => "Content3"
};

foreach ($posts as $key => $value) {
  echo $key . " - " . $value;
}

Common Functions

echo (multiple values), print (single value), print_r (for arrays).

When debugging, use var_dump for more info or var_export for type representation.

Requests

To set a cookie, use setcookie(name, value, exp).

References

1. https://www.learn-php.org/en/Hello%2C_World%21
2. https://piped.kavin.rocks/watch?v=BUCiSSyIGGU
3. https://www.php.net/manual/en/language.variables.superglobals.php
4. https://www.php.net/manual/en/function.filter-input.php
5. https://stackoverflow.com/questions/3812526/conditional-statements-in-php-code-between-html-code
6. https://www.tutorialspoint.com/php/php_sending_emails.htm

Last modified: 202212070107