正则表达式将大写变为小写

Question

I am trying to change it all to lower case letters. It works if the word is all uppercase, but if only 1 letter in the word is uppercase it does not change it. I would really appreciate it if someone fixed my code.

<?php
$x = "HELLO WORLD! THIS is a test";
echo preg_replace_callback('/\b([A-Z]+)\b/', function($word) {
   return strtolower($word[1]);
}, $x);
?>

Answer 1

\b matches a word-boundary. So you can achieve your goal just omit \b's in your regex. Try this:

<?php
$x = "HELLO WORLD! THIS is a test";
echo preg_replace_callback('/([A-Z]+)/', function($word) {
    return strtolower($word[1]);
}, $x);
?>