- print_r: documentation ( source)
- strtoupper: documentation ( source)
- array_walk_recursive: documentation ( source)
<?php
$a = [
['a', 'b', 'c'],
['d', 'e', 'f'],
];
array_walk_recursive($a, function(&$v) { $v = strtoupper($v); } );
print_r($a);