Character Case in PHP

Given a string:

<?php
	$str = 'php';
?>

Convert this string into the following:

'PHP'

Given a string:

<?php
	$str = 'PHP';
?>

Convert this string into the following:

'php'

Given a string:

<?php
	$str = 'london';
?>

Convert this string into the following:

'London'

Given a string:

<?php
	$str = 'London';
?>

Convert this string into the following:

'london'

Given a string:

<?php
	$str = 'london is the capital of great britain';
?>

Convert this string into the following:

'London Is The Capital Of Great Britain'

Given a string:

<?php
	$str = 'LONDON';
?>

Convert this string into the following:

'London'

Given a string:

<?php
	$str = 'привет';
?>

Convert this string into the following:

'ПРИВЕТ'

Given a string:

<?php
	$str = 'ПРИВЕТ';
?>

Convert this string into the following:

'привет'