How do you use the replace function in PHP?

In PHP, the replace function is mainly used to replace specified content in a string. The common replace functions include the following:

1. str_replace(): Replace all occurrences of a string with a new string.
   Syntax: str_replace(search string, replace string, original string [, replace count])
   Example: $new_string = str_replace(“world”, “PHP”, $string);
2. str_ireplace() function is used to replace all matching occurrences of a string with a new string, without considering case sensitivity. The syntax is str_ireplace(search string, replace string, original string [, number of replacements]). Example: $new_string = str_ireplace(“WORLD”, “PHP”, $string);
3. preg_replace(): Replaces all occurrences of a pattern in a string with a new string using regular expressions.
   Syntax: preg_replace(pattern, replacement string, original string [, replace count])
   Example: $new_string = preg_replace(“/\d+/”, “number”, $string);
4. strtr(): Replace characters in a string according to specified rules.
   Syntax: strtr(original string, rules)
   Example: $new_string = strtr($string, “abc”, “123”);

You can use these replacement functions to perform necessary substitutions and get the updated string. Please choose the appropriate replacement function based on your specific needs.