PHP has 1000+ built-in functions. These are the most important categories.
date("Y-m-d")time() — Unix timestampstrtotime("next Monday")file_get_contents()file_put_contents()json_encode($arr)json_decode($str, true)preg_match($pattern, $str)preg_replace($pattern, $replace, $str)<?php
// Date
echo date("Y-m-d H:i:s"); // 2025-05-01 14:30:00
echo date("l, F j, Y"); // Thursday, May 1, 2025
// JSON
$data = ["name"=>"Alice","age"=>25];
$json = json_encode($data); // {"name":"Alice","age":25}
$back = json_decode($json, true); // back to array
// Regex
preg_match("/\d+/", "abc123def", $m);
echo $m[0]; // 123
$clean = preg_replace("/[^a-zA-Z0-9]/", "", "hello@world!");
echo $clean; // helloworld
?>