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This article mainly introduces what the useful regular expressions are, which can be used for reference. Interested friends can refer to them. I hope you will gain a lot after reading this article.

Regular expression, also known as regular representation, conventional representation. (English: Regular Expression, often abbreviated as regex, regexp or RE in code), a concept in computer science. Regular expressions use a single string to describe and match a series that conforms to a syntactic rule. In many text editors, regular expressions are often used to retrieve and replace text that matches a certain pattern.

I. Classification

1. "^" the same kind

"^" matches the starting position of the input string.

"$" matches the end of the input string.

"\ b" matches a word boundary, that is, the position between the word and the space. (for example: "er\ b" can match "er" in "never", but not "er" in "verb")

"\ B" as opposed to "\ b" matches non-word boundaries (for example: "er\ b" can match "er" in "verb", but not "er" in "never")

2. "*" the same kind

Asterisk (*): an asterisk indicates that the character preceding it is matched any number of times (0 or any times).

Plus sign (+): indicates that the preceding characters are matched one or more times (at least once).

Question mark (?): a question mark is also a quantifier, which means to match the previous character 0 or 1 times.

Square brackets []: brackets are used to represent a set of characters. It would be too troublesome to write in brackets one by one if there are many elements, such as 26 letters, numbers, etc., so we usually use hyphens to represent a range (for example: [AMAZ] represents a collection of lowercase letters; [a-zA-Z] represents a collection of uppercase and lowercase letters). A delimited "^" means to match any characters that are not in the collection. (for example: [^ aMuz]).

Curly braces {}: the function of curly braces is to repeat the previous character many times (for example: {N}: repeat n times; {n ·m}: repeat n times; {n,}: repeat at least n times; {, m}: repeat m times at most)

3. "\ s" the same kind

"\ w" (lowercase w) represents a letter or number, equivalent to [a-zA-Z0-9]

"\ W" (capital W) means non-alphabetic and non-numeric, as opposed to\ w and equivalent to [^ a-zA-Z0-9]

"\ s" (lowercase s) means to match an empty character, including spaces, line breaks, carriage returns, tab, which is equivalent to [\ n\ r\ t\ f]

"\ S" (capital S) matches non-space characters, as opposed to\ s, which is equivalent to [^\ n\ r\ t\ f]

"\ d" (lowercase d) represents a decimal number, which is equivalent to [0-9]

"\ D" (uppercase D) matches a non-numeric character, equivalent to [^ 0-9]

Declare a checkNum function

Function checkNum (input) {/ * indicates that it must be one or more digits * / var regex = / ^ [Amurz] {6, if (input.match (regex)) {return true;} else {return false;}}

Declare a checkEmail function

Function checkEmail (input) {var regex = / ^\ w+ ([- +.]\ w+) * @\ w+ ([-.]\ w+) *\.\ w+ ([-.]\ w+) * $/; if (input.match (regex)) {return true;} else {return false;}

4. Encapsulate a trim ()

Var my = function () {}; my.prototype = {ltrim: function (str) {return str.replace (/ (^\ s*) / g journal');}, rtrim: function (str) {return str.replace (/ (\ s) $) / g journal');}, trim: function (str) {return str.replace (/ (^\ s *) | (\ s *) / g camera') }} / * ^ begins with xx * / / *\ s for spaces * / / * means to match zero or more * / / * g means to match all * / / * (^\ s *) means to match one or more characters that begin with spaces * / / * str.replace (/ (^\ s*) / gazillion') means to replace all spaces with''

Attachment: a complete collection of commonly used regular expressions! (for example: match Chinese, match html)

Regular expression that matches Chinese characters: [u4e00-u9fa5]

Note: matching Chinese is really a headache. It's easy to have this expression.

Match double-byte characters (including Chinese characters): [^ x00-xff]

Note: can be used to calculate the length of a string (a double-byte character length meter 2 ~ ~ ASCII character counter 1)

A regular expression that matches a blank line: ns*r

Comment: can be used to delete blank lines

Regular expression that matches the HTML tag:] * >. *? |

Commentary: the version circulated on the Internet is too bad, the above one can only match part of it, and there is still nothing I can do about complex nested tags.

Regular expression that matches the leading and trailing white space characters: ^ s* | slots $

Comment: a very useful expression that can be used to delete white space characters (including spaces, tabs, page feeds, etc.) at the beginning and end of a line

Regular expression that matches the Email address: W + ([- +.] w +) * @ w + ([-.] w +) * .w + ([-.] w +) *

Comment: form validation is very useful

Regular expression that matches the URL URL: [a-zA-z] +: / / [^ s] *

Note: the function of the version circulated on the Internet is very limited, and the above version can basically meet the needs.

Whether the matching account is legal (5-16 bytes are allowed at the beginning of the letter, and alphanumeric underscores are allowed): ^ [a-zA-Z] [a-zA-Z0-9 _] {4j 15} $

Comment: form validation is very useful

Match domestic phone number: d {3}-d {8} | d {4}-d {7}

Commentary: matching forms such as 0511-4405222 or 021-87888822

Match Tencent QQ number: [1-9] [0-9] {4,}

Commentary: Tencent QQ starts from 10000

Match the postcode of China: [1-9] d {5} (?! d)

Commentary: the postal code of China is 6 digits

Match ID: d {15} | d {18}

Commentary: Chinese ID cards are 15 or 18 digits

Match the ip address: dong.dharm.ding.d+

Note: useful when extracting ip addresses

Match specific numbers:

^ [1-9] $/ / match positive integers

^-[1-9] $/ / match negative integers

^ -? [1-9] d _ match $/ / match integer

^ [1-9] d * | 0 $/ / matches a non-negative integer (positive integer + 0)

^-[1-9] d * | 0 $/ / matches non-positive integers (negative integers + 0)

^ [1-9] dquo.d* | 0.d* [1-9] droom$ / / matches positive floating point numbers

^-([1-9] dfol.d* | 0.d* [1-9] d*) $/ / matches negative floating point numbers

^ -? ([1-9] droom.d* | 0.d* [1-9] d* | 0room.0+ | 0) $/ / match floating point number

^ [1-9] dfol.d* | 0.d* [1-9] d* | 0room.0+ | 0 $/ / match non-negative floating point number (positive floating point number + 0)

^ (- ([1-9] dfu.d* | 0.d* [1-9] d*)) | 0room.0+ | 0 $/ / matches non-positive floating point numbers (negative floating point numbers + 0)

Commentary: useful when dealing with a large amount of data, pay attention to corrections in specific applications

Match a specific string:

^ [A-Za-z] + $/ / matches a string of 26 English letters

^ [Amurz] + $/ / matches a string of 26 English letters in uppercase

^ [amurz] + $/ / matches a string of 26 lowercase letters

^ [A-Za-z0-9] + $/ / matches a string of numbers and 26 letters

^ wrist $/ / matches a string consisting of numbers, 26 letters, or underscores

You can only enter a number: "^ [0-9] * $"

Only n-digit numbers can be entered: "^ d {n} $"

You can only enter at least n digits: "^ d {n,} $"

You can only enter the number of mmurn digits: "^ d {mdirection n} $"

You can only enter zero and non-zero numbers: "^ (0 | [1-9] [0-9] *) $"

You can only enter positive real numbers with two decimal places: "^ [0-9] + (. [0-9] {2})? $"

You can only enter positive real numbers with 1-3 decimal places: "^ [0-9] + (. [0-9] {1pr 3})? $"

You can only enter a positive integer that is not zero: "^ +? [1-9] [0-9] * $"

You can only enter a negative integer that is not zero: "^-[1-9] [0-9] * $"

Only characters of length 3 can be entered: "^. {3} $"

You can only enter a string of 26 letters: "^ [A-Za-z] + $"

You can only enter a string of 26 capital letters: "^ [Amurz] + $"

You can only enter a string of 26 lowercase letters: "^ [amurz] + $"

You can only enter a string of numbers and 26 letters: "^ [A-Za-z0-9] + $"

You can only enter a string consisting of numbers, 26 letters, or an underscore: "^ wicked $"

Verify the user password: "^ [a-zA-Z] w {5pm 17} $" is in the correct format: begins with a letter and is between 6 and 18 in length

Can only contain characters, numbers, and underscores.

Verify that it contains characters such as ^% &',; =? $":" [^% &',; =? $x22] + "

You can only enter Chinese characters: "^ [u4e00-u9fa5], {0,} $"

Verify the Email address: "^ w + [- +.] w +) * @ w + ([-.] w +) * .w + ([-.] w +) * $"

Verify InternetURL: "^ http://([w-]+.)+[w-]+(/[w-./?%&=]*)?$"

Verify the phone number: "^ ((d {3pr 4}) | d {3pr 4} -)? d {7pr 8} $"

The correct format is "XXXX-XXXXXXX", "XXXX-XXXXXXXX", "XXX-XXXXXXX"

"XXX-XXXXXXXX", "XXXXXXX", "XXXXXXXX".

Verify ID number (15 or 18 digits): "^ d {15} | d {} 18 $"

Verify the 12 months of the year: "^ (0? [1-9] | 1 [0-2]) $" the correct format is: "01"-"09" and "1"12"

Verify 31 days of a month: "^ ((0? [1-9]) | (1 | 2) [0-9]) | 30 | 31) $"

The correct formats are "01", "09" and "1"31".

Regular expression that matches Chinese characters: [u4e00-u9fa5]

Match double-byte characters (including Chinese characters): [^ x00-xff]

Regular expression that matches blank lines: n [s |] * r

Regular expression that matches the HTML tag: /. * | /

Regular expression that matches leading and trailing spaces: (^ s*) | (sworn $)

Regular expression that matches the Email address: W + ([- +.] w +) * @ w + ([-.] w +) * .w + ([-.] w +) *

Regular expression that matches the URL URL: http://([w-]+.)+[w-]+(/[w-. /?% & =] *)? * /

Thank you for reading this article carefully. I hope the article "what are the useful regular expressions" shared by the editor will be helpful to everyone? at the same time, I also hope that you will support and pay attention to the industry information channel. more related knowledge is waiting for you to learn!

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