如何使用PHP正则表达式压缩空格字符？

Question

$string = 'Hello    this is a bunch of numbers: 333 and letters and $pecial Characters@!*(';

$foo = preg_replace("/[^a-zA-Z0-9\s]/", "", $string);

echo $foo;

The above returns:

Hello    this is a bunch of numbers 333 and letters and pecial Characters

I want to retain spaces but not if theres more than one. How can that be done?

It should look like:

Hello this is a bunch of numbers 333 and letters and pecial Characters

Answer 1

$foo = preg_replace("/[^a-zA-Z0-9\s]/", "", $string);
$foo = preg_replace('/\s+/',' ',$foo);