Regular Expressions---tools that look hard but are easy to use

Regular expressions, we may be intimidated by its complex expressions, but what I'm going to tell you is that as long as you step through it, you will find that the regular expression is not as difficult as you might think , and that the appearance of it will give us a lot of code to write about, and verify that the content is very accurate. Now that you can easily validate your data with regular expressions, what is a regular expression?

1. Definition:

When writing a program or Web page that handles strings, there is often a need to find strings that match certain complex rules. Regular Expressions are the tools used to describe these rules . In other words, the regular expression is the code that records the text rule . the RegExp object is an abbreviation for regular expression (regular expressions).

Note: The regular expression engine typically provides a "test whether a specified string matches a regular expression" method, such as the Regexp.test () method in JavaScript or theRegex.IsMatch () method in. Net . The match here refers to the part of the string that matches the expression rule. If you do not use ^ and $ , for \d{5,12} , the use of such a method can only guarantee that the string contains 5 to 12 consecutive digits , Instead of the entire string, it's 5 to 12 digits .

2. The best way to learn a regular expression is to start with an example and then modify the example yourself to experiment. Here are a few simple examples, and they are described in detail.

Suppose you look in an English novel for hi , you can use regular expressions hi . Typically, a tool that handles regular expressions provides an option to ignore the case (/i), and if this option is selected, it can match hi , hi , HI , HI any of these four cases.

Hi two consecutive characters, such as him , history , high and so on. With hi to find, Hi will also be found. If you want to to find the word hi exactly , we should use \bhi\b .

is a special code prescribed by regular expressions (well, some people call it metacharacters, metacharacter), which represents the beginning or end of a word, that is, the boundary of a word . Although English words are usually delimited by spaces, punctuation marks, or line breaks, \b does not match any of these word-delimited characters, it only matches one position .

If you're looking for a hi, not far behind, follow a Lucy, you should use \bhi\b.*\blucy\b.

used ^ and $ , so the entire string entered is to be used and \d{5,12} to match, which means the entire input must be 5 to 12 digits , so if you enter the QQ number to match the regular expression, then it will meet the requirements.

        $ (function  () {            var value = $ ("#mybutton"). Val ();             var regvalue =/^\d{5,12}$/;             if true {                alert (' verify success! ');            }        })     </script>
Results:
3. character escapes
If you want to find the meta-character itself, such as when you look up  , or  *, there's a problem: You can't specify them, because they'll be interpreted as something else. Then you have to use  \ to cancel the special meaning of these characters. Therefore, you should use  \. and  \*. Of course, to find  \ itself, you also have to use  \ \.     
For example:deerchao\.net matches  deerchao.net,c:\\windows matches  C:\Windows. 
4. Branch conditions
The   branching condition in the expression refers to several rules that should be matched if any of these rules are met, by  | Separate the different rules. Don't you understand? Okay, look at the example:
0\d{2}-\d{8}|0\d{3}-\d{7} This expression can  match two phone numbers separated by hyphens: one is a three-bit area code, a 8-bit local number (such as 010-12345678), a 4-bit area code, and a 7-bit local number ( 0376-2233445).
5. Grouping
You can use parentheses to specify  sub-expressions (also called  groupings ) 
  is a  simple IP address matching  expression. To understand this expression, parse it in the following order: \d{1,3}  matches 1 to 3 digit ,  (\d{1,3}\.) {3}  Match  three digits plus an English period (this whole is the   group  , and finally add  a one-to-three-digit number  ( \d{1,3} ). 
6. Anti-righteousness
Today's explanation to here, I hope that we have a harvest, the most important is the regular expression of practice, practice more, the natural use of good (make perfect Yo),
See you next time!
Regular Expressions---tools that look hard but are easy to use