What are the common pitfalls when using str_replace and preg_replace functions in PHP?

Common pitfalls when using str_replace and preg_replace functions in PHP include not escaping special characters properly, not using the correct syntax for regular expressions, and not handling case sensitivity appropriately. To solve these issues, it is important to carefully review the documentation for these functions and ensure that special characters and regular expressions are used correctly.

// Example of using str_replace with proper escaping of special characters
$search = "world";
$replace = "PHP";
$string = "Hello, world!";
$new_string = str_replace($search, $replace, $string);
echo $new_string;