01. regular expression overview

1. Overview of regular expressions

Regular expressions , It's actually a 「 Regular expressions 」, We set the rules , You can match the desired data from a string .

stay Wikipedia On , We see 「 Regular expressions 」 The description is as follows ：

Regular expressions （ English ：Regular Expression, Often abbreviated to regex、regexp or RE）, also called Regular expressions 、 Regular representation 、 Regular expressions 、 Conventional representation , It's a concept of computer science . Regular expressions are described using a single string 、 Match a string that matches a syntax rule . In many text editors , Regular expressions are often used for retrieval 、 Replace the text that matches a pattern .

Many programming languages support string manipulation with regular expressions . for example , stay Perl A powerful regular expression engine is built in . The concept of regular expression was originally developed by Unix Tool software in （ for example sed and grep） Popular .

And more simply to understand , In fact, that is 「 Take a mold , Get the data you want 」.

in addition , Regular expressions are an indispensable technique in programming , Especially now people like to use Python To implement a web crawler , But also can realize its powerful and charm .

2. Common cases （ cell-phone number 、 Email verification ）

like , When you log on to a website , An account can be a mailbox , It can also be a mobile phone number . here , The system will always check whether the format of your email or mobile number is correct , Then judge whether there is this user in the system .

If the format you entered is incorrect , The system will prompt , How does it match and validate the information you enter ？

such as , The format of the mobile number matches , Including Chinatelecom 、 China Unicom 、 China Mobile 、 China Radio and television 、 Wireless network card 、 Virtual operators, etc , Our regular expressions can be written like this ：

/^(13[0-9]|14[01456879]|15[0-35-9]|16[2567]|17[0-8]|18[0-9]|19[0-35-9])\d{8}$/

also , The format of the mailbox matches , Just keep it simple ：

/^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/

I can't understand it now , It doesn't matter , More complicated content , We will open them one by one and introduce them to you in detail , I can understand it right away , Very simple .