What is the PHP reference?

The PHP reference on SyntaxStudy lists all 25 PHP elements, properties, and methods with syntax explanations and working code examples. It is a complete, beginner-friendly cheat sheet for PHP developers.

Is this PHP reference free?

Yes. The entire PHP reference on SyntaxStudy is completely free. No account or payment is required to browse all 25 entries.

The best way to learn PHP is to start with the free PHP tutorial on SyntaxStudy. Each lesson includes a hands-on code example you can run in the browser, followed by a short quiz. After completing the tutorial, use this reference page to look up syntax whenever you need it.

PHP Reference — Complete List with Examples

String Functions

Name	Syntax	Description
strlen()	`strlen(string $string): int`	Returns the length of a string in bytes. Use mb_strlen() for multibyte/Unicode strings.	Details →
str_replace()	`str_replace(mixed $search, mixed $replace, mixed $...`	Replaces all occurrences of the search string with the replacement string. Case-sensitive.	Details →
strpos()	`strpos(string $haystack, string $needle, int $offs...`	Finds position of first occurrence of a substring. Returns false if not found — always use strict comparison (!==).	Details →
substr()	`substr(string $string, int $offset, ?int $length =...`	Returns part of a string, starting at offset for the given length. Negative offset counts from the end.	Details →
strtolower() / strtoupper()	`strtolower(string $string): string`	Converts a string to lowercase or uppercase. Use mb_ variants for multibyte/Unicode text.	Details →
trim()	`trim(string $string, string $characters = " \n\r\t...`	Strips whitespace from both ends of a string. ltrim() strips left only; rtrim() strips right only.	Details →
explode() / implode()	`explode(string $separator, string $string): array`	explode() splits a string into an array by separator; implode() (alias: join) joins an array into a string.	Details →
sprintf()	`sprintf(string $format, mixed ...$values): string`	Returns a formatted string. Common specifiers: %s (string), %d (integer), %f (float), %05d (zero-padded).	Details →
preg_match() / preg_replace()	`preg_match(string $pattern, string $subject, array...`	preg_match() performs a regex search returning match count; preg_replace() replaces regex matches.	Details →
htmlspecialchars()	`htmlspecialchars(string $string, int $flags = ENT_...`	Converts special HTML characters to entities. Essential for preventing XSS when outputting user data.	Details →

Array Functions

Name	Syntax	Description
array_map()	`array_map(?callable $callback, array $array): arra...`	Applies a callback to each element of an array and returns a new array of results.	Details →
array_filter()	`array_filter(array $array, ?callable $callback = n...`	Filters array elements using a callback. Without callback, removes all falsy values (0, "", null, false).	Details →
array_reduce()	`array_reduce(array $array, callable $callback, mix...`	Iteratively reduces an array to a single value using a callback function.	Details →
array_merge()	`array_merge(array ...$arrays): array`	Merges arrays. String keys from later arrays overwrite; numeric keys are re-indexed.	Details →
usort()	`usort(array &$array, callable $callback): true`	Sorts array in place using a user-defined comparison function. Use the spaceship operator <=> for concise comparisons.	Details →
in_array() / array_key_exists()	`in_array(mixed $needle, array $haystack, bool $str...`	in_array() checks if a value exists; array_key_exists() checks if a key exists in an array.	Details →
array_unique()	`array_unique(array $array): array`	Removes duplicate values from an array. Keys are preserved; use array_values() to re-index.	Details →
array_slice()	`array_slice(array $array, int $offset, ?int $lengt...`	Returns a portion of an array without modifying the original. Useful for pagination.	Details →

Math Functions

Name	Syntax	Description
round() / floor() / ceil()	`round(float $num, int $precision = 0): float`	round() rounds to specified decimal places; floor() always rounds down; ceil() always rounds up.	Details →
rand() / random_int()	`rand(int $min, int $max): int`	Generates a random integer. Use random_int() for cryptographically secure randomness.	Details →

Date Functions

Name	Syntax	Description
date()	`date(string $format, ?int $timestamp = null): stri...`	Formats a Unix timestamp as a date/time string. Uses current time when no timestamp is given.	Details →
strtotime()	`strtotime(string $datetime): int\|false`	Parses an English textual datetime description into a Unix timestamp.	Details →
DateTime class PHP 5.2	`new DateTime(string $datetime = "now", ?DateTimeZo...`	Object-oriented date/time handling with timezone support and easy arithmetic via modify() and diff().	Details →

File Functions

Name	Syntax	Description
file_get_contents() / file_put_contents()	`file_get_contents(string $filename): string\|false`	Read an entire file into a string or write a string to a file in a single call.	Details →
file_exists() / is_file() / is_dir()	`file_exists(string $filename): bool`	Check if a file or directory exists. is_file() confirms a regular file; is_dir() confirms a directory.	Details →