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This article will explain in detail about the syntax of Flex regular expressions. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

Flex regular expression

1. Basic grammar

. Matches any single character except the newline character "\ n".

* matches zero or more occurrences of the previous Flex regular expression.

Eg:trace ("ThisBookIsGoodBoooookBoxBx." .replace (/ Bo*g, "Coo"))

ThisCookIsGoodCookCooxCoox

+ matches one or more occurrences of the previous Flex regular expression.

Eg:trace ("ThisBookIsGoodBoooookBoxBx." .replace (/ Bo+/g, "Coo"))

ThisCookIsGoodCookCooxBx

? Represents the items that appear before it, with or without.

Eg:trace ("ThisBookisGoodBook". Replace (/ G?oo/g, "Coo"))

ThisBCookisCoodBCook.

{} varies according to what is in parentheses. A single number {n} means that the previous pattern is repeated n times, such as: [Amurz] {3}; {N1 n1-n2 N2}; {name} indicates that it is replaced with a name.

Eg: {n} the items that appear before it must be repeated n times, {n,} the items that appear before it must be repeated at least n times, and the items that appear before it are repeated n to m times.

Trace ("ThisBookidgoodBoooooookBok" .replace (/ Bo {3,} k _ G, "_))

ThisBookidgood_Bok

() groups a series of Flex regular expressions. Each of "*", "+", and "{}" acts directly on the expression on its left, while "|" usually affects the expression on the left and everything on the right.

Eg: the string is grouped into a group that requires zero or more repeats of the string Go followed by A.

Trace (AGoGoIsAnameAGo'Sfather ".replace (/ A (Go) * / g," _ "))

_ Is_name_'sfather

[] matches any character in parentheses. Use "-" to indicate the range of characters. If the * * character is the suppressed symbol "^", then its meaning becomes to match the character in parentheses to aid any character, and the table antonym.

Eg1:trace ("my Book price is 45 yuan" .replace (/ [^ 0-9a-z] / g, "*"))

* ook***45*

Eg2:trace (AGoGoIsAonameAGo'Sfather ".replace (/ A [go] / g," _ "))

_ oGoIs_name_o'sfather

\ if it is followed by a lowercase letter, it is a C escape sequence, otherwise the following characters are referenced.

"..." Match the contents in quotation marks

Matches the previous expression only if the following expression is followed.

The * * character of the ^ Flex regular expression, which matches the beginning of the line; it is used for negation in square brackets, and there is no special case otherwise.

Trace ("ABAEF\ nABSD\ nABFFD" .replace (/ ^ AB/gm, "Hello"))

Hello, AEF.

Hello, SD.

Hello, FFD.

The * * character of the $Flex regular expression that matches the end of the line-there are no other special cases.

A column or column within the angle brackets at the beginning of a pattern so that that pattern applies only to the specified starting state.

In flex, this particular pattern matches the end of the file.

\ b matches a word boundary, that is, the position between the word and the space.

\ B matches non-word boundaries.

\ cx matches the control characters indicated by x.

\ d matches a numeric character. Equivalent to [0-9].

\ D matches a non-numeric character. Equivalent to [^ 0-9].

\ f matches a feed character. Equivalent to\ x0c and\ cL.

\ nmatches a newline character. Equivalent to\ x0a and\ cJ.

\ r matches a carriage return. Equivalent to\ x0d and\ cM.

\ s matches any white space characters, including spaces, tabs, page breaks, and so on. Equivalent to [\ f\ n\ r\ t\ v].

\ s matches any non-white space character. Equivalent to [^\ f\ n\ r\ t\ v].

\ t matches a tab. Equivalent to\ x09 and\ cI.

\ v matches a vertical tab. Equivalent to\ x0b and\ cK.

\ w matches any word characters that include underscores. Equivalent to'[A-Za-z0-9]'.

\ W matches any non-word characters. Equivalent to'[^ A-Za-z0-9]'.

\ xn matches n, where n is the hexadecimal escape value. The hexadecimal escape value must be a determined two-digit length.

\ num matches num, where num is a positive integer. A reference to the obtained match.

\ nidentifies an octal escape value or a backward reference. If there are at least n previously acquired subexpressions, n is a backward reference. Otherwise, if n is an octal number (0-7), n is an octal escape value.

\ nm identifies an octal escape value or a backward reference. If there are at least isprecededbyatleastnm acquired subexpressions before\ nm, nm is a backward reference. If there are at least n fetches before\ nm, n is a backward reference followed by the text m. If none of the previous conditions are met, if both n and m are octal numbers (0-7),\ nm will match the octal escape value nm.

two。 Grammatical extension

Flex regular expression is a general standard. Most computer languages support Flex regular expression, including as3. Here we collect some commonly used Flex regular expression statements, so you don't have to write them yourself when you use them.

^\ positive integer / match non-negative integer + 0

^ [0-9] * [1-9] [0-9] * $/ / match positive integers

^ (-\ d +) | (0 +) $/ / matches a non-positive integer (negative integer + 0)

^-[0-9] * [1-9] [0-9] * $/ / match negative integers

^ -?\ matching integer

^\ d + (\.\ d +)? $/ / matches non-negative floating point numbers (positive floating point numbers + 0)

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

^ ((-\ d + (\.\ d +)?) | (0 + (\ .0 +)?)) $/ / match non-positive floating point numbers (negative floating point + 0)

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

^ (-?\ d +) (\.\ d +)? $/ / match floating point numbers

^ [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

^\ wrought letters / matches a string consisting of numbers, 26 letters, or an underscore

^ [\ w -] + (\ .[\ w -] +) * @ [\ w -] + (\ .[\ w -] +) + $/ / matches the email address

^ [a-zA-z] +: / / match (\ w+ (-\ w+) *) (\. (\ w+ (-\ w+) *)) * (\?)? $

^ (\ d {1pr 2} | 1\ d\ d | 2 [0-4]\ d | 25 [0-5])\. (\ d {0-4] 2} | 1\ d\ d | 2 [0-4]\ d | 25 [0-5])\. (\ d {0-4]\ d | 2 [0-4])\ d | 25 [0-5])\. (\ d {1 # 2} | 1\ d\ d | 2 [0-4]\ d | 25 [0-5]) $/ / match

/ / Flex regular expression that matches url matches Chinese characters: [\ u4e00 -\ u9fa5]

Match double-byte characters (including Chinese characters): [^\ X00 -\ xff]

Flex regular expression that matches blank lines:\ n [\ s |] *\ r

Flex regular expression that matches the HTML tag: /. * | /

Flex regular expression that matches leading and trailing spaces: (^\ s *) | (\ s _ blank $)

The Flex regular expression that matches the Email address:\ W + ([- +.]\ w +) * @\ w + ([-.]\ w +) *.\ w + ([-.]\ w +) *

Flex regular expression that matches the URL URL: ^ [a-zA-z] +: / / (\ w+ (-\ w+) *) (\. (\ w+ (-\ w+) *)) * (\?\ S*)? $

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} $

Match domestic phone number: (\ d {3}-|\ d {4} -)? (\ d {8} |\ d {7})?

Match Tencent QQ number: ^ [1-9] * [1-9] [0-9] * $

The following table is a complete list of metacharacters and their behavior in the context of Flex regular expressions:

\ Mark the next character as a special character, or a literal character, or a backward reference, or an octal escape character.

^ matches the starting position of the input string. If the Multiline property of the RegExp object is set, ^ also matches the position after'\ n'or'\ r'.

$matches the end of the input string. If the Multiline property of the RegExp object is set, $also matches the position before'\ n'or'\ r'.

* matches the previous subexpression zero or more times. + matches the previous subexpression one or more times. + is equivalent to {1,}.

? Matches the previous subexpression zero or once. ? It is equivalent to {0jue 1}. {n} n is a non-negative integer that matches a determined n times.

{n,} n is a non-negative integer that matches at least n times. {n ·m} m} m and n are non-negative integers, where n

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