NSWI142: Web Applications

Cheatsheet: How to run PHP

Be careful which PHP version you are running - you want at least version 8. Older versions may lack some features. Check Supported Versions.

• Use one of many online compilers, e.g. [1], [2], [3].
• Use PHP from a command line by running php file.php. You can:
  • use our Webik server via SSH
  • install it on your own
  • use a Docker image
• Use a web server with PHP support.
  • On Webik, upload PHP file into public_html directory and open
    webik.ms.mff.cuni.cz/~<username>/file.php.
  • Install XAMPP / MAMP / LAMP / WAMP on your own computer.
  • Use built-in server by running php -S localhost:8080 from your project directory.

Cheatsheet: PHP: Hypertext Preprocessor

Input:

This text is sent <strong>a⁠s is</strong> without any modifications.
<?php
  // We are inside PHP script that is executed by PHP preprocessor
  echo 'The time is ' . date('H:i:s');
?>

Again, this text is sent a⁠s is.
    

Output:

This text is sent as is without any modifications.
The time is 04:20:00
Again, this text is sent as is.
    

Cheatsheet: PHP Variables and types

<?php

$age = 42;
$message = "Your age is $age"; // double quotes interpolate, single quotes do not
$fullMessage = $message . "\nWelcome."; // concatenation uses .

echo($message);
echo $message; // echo is actually language construct, so you can write it without parentheses

var_dump($fullMessage); // dump (print) any variable

$age = 'John Doe'; // dynamically typed language: variable can change its type

$pi = 3.14; // float
$isAdult = true; // boolean
$nothing = null; // null

$userProvidedName = 'John <img src="pepe_hacker.png"> Doe';
// escape dangerous strings before outputting them to HTML
echo 'Hello user ' . htmlspecialchars($userProvidedName);
// Hello user John &lt;img src="pepe_hacker.png"&gt Doe
    

Cheatsheet: Control Structures

<?php

if ($name === 'John') {
  ...
} else {
  ...
}

while ($x >= 0) {
  ...
}

do {
  ...
} while (strlen($text) > 0)

for ($i = 0; $i < 3; $i++) {
  ...
}
    

Cheatsheet: Arrays

<?php

$food = [ 'apple', 'tomato', 'pear' ]; // indexed
$user = [ 'name' => 'Joe', 'id' => 42 ]; // associative (like Python dict)
$empty = [];

// Access
$food[0]; // 'apple'
$user['name']; // 'Joe'

$food[] = 'banana'; // append
$last = array_pop($food); // pop from end

// Existence checks
isset($user['name']); // true if key exists and not null
array_key_exists('name', $user); // true even if null

// Looping through array
foreach ($array as $value) { echo $value } // $value is a copy
foreach ($array as &$value) { $value *= 2; } // & mutates original
foreach ($array as $key => $value) { echo "$key: $value\n" }
    

Cheatsheet: Working with JSON

<?php

$data = [ 'name' => 'Joe', 'skills' => [ 'math', 'code' ], 'id' => 42 ];

// Encode: returns JSON string
$json = json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
echo $json;

// Decode to an associative array (similar to a Python dictionary)
$array = json_decode($json, true); // true => associative array
$array['name'];
    

<?php

file_put_contents('data.json', $stringData); // write string to file
$content = file_get_contents('data.json'); // read string from file

// You can append to the file and obtain an exclusive lock to prevent concurrency issues
file_put_contents('data.json', $stringData, FILE_APPEND | LOCK_EX);
    

Where to find documentation?

The official PHP documentation is available at php.net/docs.php.

Examples:

• htmlspecialchars
• file_put_contents

Comparisons in PHP

Prefer strict comparisons (===, !==) to avoid unexpected type conversion.

Only use loose comparisons (==, !=) when you need it.

<?php

42 == '42'; // true (type conversion)
42 === '42'; // false (different types)

$var = 0;
$var == false; // true (type conversion)
!$var; // (not operator applied to zero) true (type conversion)
$var === false; // false (different types)
    

strpos(string $haystack, string $needle, int $offset = 0): int|false - Finds the position of the first occurrence of a substring in a string. Returns 0 if the substring is found at the beginning of the string, returns false if not found.

PHP Standards Recommendations

Set of standard recommendations for writing PHP code.

Check PSR-1: Basic Coding Standard and PSR-12: Extended Coding Style Guide.

<?php

methodNamesAreInCamelCase();

if ($condition) { // Spaces after if keyword, and before opening brace that MUST be on the same line
    // Code MUST use an indent of 4 spaces for each indent level, and MUST NOT use tabs for indenting.
}

for ($i = 0; $i < 10; $i++) { // Note spaces around operators
    // for body
}

// You MUST NOT close the PHP tag if you do not have any intended HTML after it