php replace every occurrence of character in string

str_replace ($search, $replace, $subject);

//replaces every occurence of $search with $replace in the string $subject
str_replace ($search, $replace, $subject);

<?php
$string = str_ireplace("FoX", "CAT", "the quick brown fox jumps over the lazy dog");
echo $string; // the quick brown CAT jumps over the lazy dog
?>