What is the difference between preg_replace() and str_replace() in PHP for string replacement?

The main difference between preg_replace() and str_replace() in PHP for string replacement is that preg_replace() allows for more advanced pattern matching using regular expressions, while str_replace() only allows for simple string matching. If you need to perform complex pattern matching and replacement, preg_replace() is the better choice. However, if you only need to replace exact strings, str_replace() is simpler and more efficient.

// Using preg_replace() for advanced pattern matching and replacement
$string = "Hello, world!";
$new_string = preg_replace('/\b(\w+)\b/', 'replacement', $string);
echo $new_string;

// Using str_replace() for simple string matching and replacement
$string = "Hello, world!";
$new_string = str_replace('world', 'universe', $string);
echo $new_string;