Most characters in a regular expression are matched exactly as entered. There are some special characters (such as $ and ^ and . ) called metacharacters, that are used for other purposes. If you want one of the metacharacters to match as a literal, it must be preceded by a back-slash ( \ ).
For example a dot (.) matches any character. If you want to match against only a dot, you need to use a back-slash in front of the dot ( \. )