Two examples are constructed below using the syntax of regular expressions as follows: The *.txt used here can be understood as a simple regular expression. Regular expressions construct patterns with specific rules, compare them with the input string information, and use them in specific functions to achieve string matching, finding, replacing, and splitting operations.įor example in our daily life, if you want to search for all txt files in a certain directory of the computer, you can enter *.txt in the directory, and then press the Enter key, you can list all the files in the directory txt format file. Regular expressions, also known as pattern expressions, have a very complete syntax system that can write patterns, and provide a flexible and intuitive string processing method.