Notes - regular expressions

What is regular expression ？

• A text mode
• Include normal characters + Special characters
• Operate on strings

Ordinary character ： for example a To z Between the letters
Special characters ： Metacharacters

Why use regular expressions ？

• Test the pattern within the string ： data validation
• replace text ： Recognize specific text with regularity , Delete the text completely or replace it with other text
• Extract substring

It has a wide range of applications

• C#
• Java
• JavaScript
• Python
• Ruby
  and so on…

grammar

A regular expression component can be a single character 、 Character set 、 character in range 、 Choice between characters or any combination of all these components .

• Ordinary character
• Nonprinting characters
• Special characters ：
  To match these special characters , You must first make the characters " escape ", The backslash character \ Put it in front of them .
• qualifiers ：
  By means of *、+ or ? Place after qualifier ?, The expression is from " greedy " The expression is converted to " Not greedy " Expression or minimum match .
• Locator ：
  Cannot use qualifier with locator .
• choice ：
  Parentheses enclose all options , Use... Between adjacent options | Separate .
  Parenthesis side effects ： Make the relevant match cached , Available at this time ?: Put the first option forward to eliminate this side effect .
• backreferences ：
  The simplest way to reverse reference 、 One of the most useful applications , It provides the ability to find a match between two identical adjacent words in the text .
  Grammar details - From the rookie tutorial
  reference： Metacharacter list + describe

Operator priority

reference： priority + describe

Matching rules

Some very simple examples 1.0
Other examples 2.0

These contents are not difficult to read , The key is how to think and use it when it comes to actual use .
so…u know Rookies start with imitation …