PHP regular expression complete tutorial 1_PHP tutorial

Regular expressions are cumbersome, but powerful. After learning them, you will not only improve your efficiency, but also give you an absolute sense of accomplishment.

At present, regular expressions have been widely used in many software, including *nix (Linux, Unix, etc.), HP and other operating systems, PHP, C#, Java and other development environments, as well as many application software. You can see the shadow of regular expressions.

The use of regular expressions can achieve powerful functions in a simple way.

In order to be simple, effective and powerful, the regular expression code is more difficult and not easy to learn.

Example: ^.+@.+..+$
Such code has scared me away many times. Maybe many people are scared away by such code.
After studying this tutorial, you will be able to apply such code freely.
　
History of regular expressions
The "ancestors" of regular expressions can be traced back to early research on how the human nervous system works. Two neurophysiologists, Warren McCulloch and Walter Pitts, developed a mathematical way to describe these neural networks.
　
In 1956, a mathematician named Stephen Kleene published a paper titled "Representation of Neural Network Events" based on the early work of McCulloch and Pitts, which introduced regular expressions. concept. Regular expressions are used to describe expressions that he calls "the algebra of regular sets," hence the term "regular expression."

It was subsequently discovered that this work could be applied to some early research using the computational search algorithms of Ken Thompson, the principal inventor of Unix. The first practical application of regular expressions was the qed editor in Unix.
　
Regular expressions have been an important part of text-based editors and search tools ever since.

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