regular-First lesson (Regular expression Basics)

I've been hearing about regular expressions, especially when I'm learning Java, and I've encountered a lot of regular expressions.
Method. For example, you can use regular expressions to restrict what you enter in an input box. Of course, after Android, the regular expression is almost useless. However, these days in the study of Python, but also encountered the concept of regular expressions. Also, many of the scripts that we work on have a regular expression in many places. Feel its knowledge point is not a lot, just want to learn under. So on the Internet, a very basic e-book, according to the contents of the book to start practicing it.
My understanding of regular expressions is a rule, a constraint. Using the universally accepted rules, these rules can be used to express complex requirements more flexibly. The specific definition of what I will not say, go straight to learn it.
According to the book method, there is a Web site that can be specifically used to verify the regular expression-regex Tester, which is a web version of the regular expression validation interface. It has two input boxes, the above input box is your regular expression content, the following box is your processing content. For example, if you type a hello in the box above, then the hello in the box below will be highlighted.
Now let's start our regular tour.

regular-First lesson (Regular expression Basics)