What are some common pitfalls to avoid when replacing characters within a string using PHP?

One common pitfall when replacing characters within a string using PHP is not using the correct function for the task. It's important to use the appropriate function, such as str_replace() or preg_replace(), depending on the specific requirements of the replacement. Additionally, not properly handling cases where the replacement string may contain special characters or patterns can lead to unexpected results.

// Example of replacing characters within a string using str_replace()
$string = "Hello, world!";
$replacedString = str_replace("world", "PHP", $string);
echo $replacedString;