Basic Introduction to Regular expressions

The basic syntax of regular expressions

1. Two special symbols ' ^ ' and ' $ '. Their role is to indicate the beginning and end of a string, respectively.

2. Other ' * ', ' + ', '? ' These three symbols represent the number of occurrences of one or a sequence of characters

The "ab{2}"---indicates that a string has an A followed by 2 B ("ABB");

"Ab{2,}"---indicates that a string has an a followed by at least 2 B;

The "ab{3,5}"---indicates that a string has an a followed by 3 to 5 B;

"ab*" = = ab{0,}

"ab+" = = Ab{1,}

"ab?" = = ab{0,1}

Note that you must specify the lower bound of the range, such as {0,2}, instead of {, 2};

3. There is also a "| representation" or "action

"Hi¦hello": Indicates a string with "hi" or "hello";
"(B¦CD) EF": denotes "bef" or "cdef";
"(a¦b) *c": Represents a String "a" "B" mixed strings followed by a "C";

4. "." can replace any character

"A.[0-9]": Indicates that a string has an a followed by an arbitrary character and a number

"^.3$": Represents a string of any three characters with a length of 3 characters s

5. Regular expression validation controls the input character type of the text box
1. Enter only numbers and English:
<input onkeyup= "Value=value.replace (/[\w]/g, ')" onbeforepaste= "Clipboarddata.setdata (' text ', Clipboarddata.getdata (' text '). Replace (/[^\d]/g, ') "id=" Text1 "name=" Text1 ">

2. Only numbers can be entered:
<input onkeyup= "Value=value.replace (/[^\d]/g, ')" onbeforepaste= "Clipboarddata.setdata (' text ', Clipboarddata.getdata (' text '). Replace (/[^\d]/g, ') "id=" Text2 "name=" Text2 ">

3. only full-width input:
<input onkeyup= "Value=value.replace (/[^\uff00-\uffff]/g, ')" onbeforepaste= "Clipboarddata.setdata (' text ', Clipboarddata.getdata (' text '). Replace (/[^\uff00-\uffff]/g, ') "id=" Text3 "name=" Text3 ">

4. Only the Chinese characters can be entered:
<input onkeyup= "Value=value.replace (/[^\u4e00-\u9fa5]/g, ')" onbeforepaste= "Clipboarddata.setdata (' text ', Clipboarddata.getdata (' text '). Replace (/[^\u4e00-\u9fa5]/g, ') "id=" Text4 "name=" TEXT4 ">

6. Application examples of regular expressions popular description

Whether the tests are all made up of numbers

:/^[0-9]{1,20}$/

Over here

^ indicates that the beginning character matches the rule immediately following the ^

$ indicates the first character to match the rule immediately preceding the $

The content in [] is an optional character set

[0-9] indicates a range of characters is required between 0-9

{1,20} indicates that the numeric string length is valid from 1 to 20, that is, the number of occurrences of the character in [0-9] is 1 to 20 times

/^ and $/should be used to represent rules that require an exact match of the entire string, rather than just a substring in the string;

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Check login name: Only 5-20 can be entered with a letter beginning with a number, underscore and '. ' The string

/^[a-za-z]{1} ([a-za-z0-9]|[. _]) {4,19}$/

Here, It is required to be composed of uppercase and lowercase letters, numbers, or special character sets [. _]

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Verify user name: Only 1-30 strings beginning with a letter can be entered

/^[a-za-z]{1,30}$/

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Check password: Only 6-20 letters, numbers, underscores can be entered

/^ (\w) {6-20}$/

Here, \w: used to match letters, numbers, or underscore characters

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Verify the regular phone, fax number: can be "+" or the beginning of the number, can contain "-" and ""

/^[+]{0,1} (\d) {1,3}[]? ([-]? ((\d) | []) {1,12}) +$/

\d: Used to match numbers from 0 to 9;

“?” Metacharacters stipulate that their leading objects must appear consecutively 0 or one time in the target object

Can match the string such as: +123-999 999; +123-999 999; 123 999 999; +123 999999 etc.

Basic Introduction to Regular expressions