Regular expression is a logical formula for string operation, that is, a "regular string" is composed of some predefined specific characters and their combinations, and this "regular string" is used to express a filtering logic for strings.

The characteristics of regular expressions are: 1. Very flexible, logical and functional; 2. The complex control of character strings can be quickly realized in a very simple way. 3. For people who have just come into contact, it is rather obscure.