PHP 8 reference · String Functions

PHP strtolower() Function

Convert every ASCII letter in a string to lowercase. Since PHP 8.2 it ignores the locale; use mb_strtolower() for é, Ü and others.

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Syntax

strtolower(string $string): string

Parameter	Description
`string`	The input string.

The lowercased string.

Lowercase textTry it yourself

<?php
echo strtolower("Hello World"), "\n";
echo strtolower("[email protected]"), "\n";

Output

hello world
[email protected]

Compare without caring about caseTry it yourself

<?php
$answer = "YES";
if (strtolower($answer) === "yes") {
    echo "Confirmed\n";
}

Output

Confirmed

Version	Change
PHP 4.0	Added
PHP 8.2	Case conversion no longer depends on the locale: only ASCII letters A–Z change.

strtoupper() · Convert every ASCII letter in a string to uppercase. Letters such as é stay unchanged; use mb_strtoupper() for those.
mb_strtolower() · Convert a string to lowercase, including letters outside ASCII such as É, Ü and Cyrillic. The Unicode-aware strtolower().
ucfirst() · Make the first character of a string uppercase and leave the rest as it is. Only ASCII letters change.
strcasecmp() · Compare two strings without caring about ASCII upper and lower case. Returns 0 if they match.
PHP Strings · tutorial