Replace multiple characters using preg_replace

<?php
$string = 'A sample string with @@@@@@@@@@@@';
echo $string;

$str2 = trim(preg_replace('/@+/', '@', $string));
echo $str2;

// Remove multiple spaces
$string = 'A '; // lot of spaces after 'A'
echo trim(preg_replace('/\s+/', ' ', $string))
?>