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This article will explain in detail how the basic grammar of regular expressions is. 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.

A regular expression is a text pattern that includes ordinary characters (for example, letters between an and z) and special characters (called metacharacters). The pattern describes one or more strings to match when searching for text.

1. Basic syntax of regular expressions

Two special symbols'^ 'and' $'. Their function is to indicate the beginning and end of a string, respectively. Examples are as follows:

"^ The": represents all strings starting with "The" ("There", "The cat", etc.)

"of despair$": a string that therefore ends in "of despair"

"^ abc$": a string that starts and ends with "abc"-- hehe, only "abc" itself.

"notice": represents any string that contains "notice".

Like the last example, if you don't use two special characters, you are indicating that the string you are looking for is in any part of the string being found-- you and

Don't position it at a certain top.

Others are'*','+ 'and'?' These three symbols represent the number of repetitions of a character or a sequence of characters. They mean "no or" respectively.

"more", "once or more" and "none or once". Here are a few examples:

"ab*": indicates that a string has an a followed by zero or more b. "a", "ab", "abbb",. )

"ab+": indicates that a string has an a followed by at least one b or more

"ab?": indicates that a string has an a followed by zero or a b

"a blank $": indicates that there are zero or one a followed by one or more b at the end of the string.

You can also use ranges, enclosed in curly braces, to indicate the range of repetitions.

"ab {2}": indicates that a string has an a followed by two b ("abb")

"ab {2,}": indicates that a string has an a followed by at least 2 b

"ab {3pr 5}": indicates that a string has an a followed by 3 to 5 b.

Please note that you must specify the lower limit of the range (for example: "{0jue 2}" instead of "{, 2}"). Also, you may have noticed,'*','+ 'and

'?' Equivalent to "{0,}", "{1,}" and "{0jin1}".

There is also a "OR" operation, which means "OR":

"hi hello": indicates that there is "hi" or "hello" in a string

"(baked cd) ef": indicates "bef" or "cdef"

"(a roomb) * c": indicates a string of "a" and "b" mixed strings followed by a "c"

'.' You 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 (3 characters in length)

Square brackets indicate that certain characters are allowed to appear at a specific location in a string:

"[ab]": indicates that a string has a "a" or "b" (equivalent to "a roomb")

"[a murd]": indicates that a string contains one of the lowercase'a'to'd'(equivalent to "an abcd" or "[murd]").

"^ [a-zA-Z]": represents a string that begins with a letter

"[0-9]%": a number that is preceded by a percent sign

", [a-zA-Z0-9] $": indicates that a string ends with a comma followed by a letter or number.

You can also use'^'in square brackets to indicate unwanted characters.'^ 'should be in the first place in square brackets. (for example: "% [^ a-zA-Z]%" table

There should be no letters in the two percent signs.

In order to express verbatim, you must add the transfer character'\ 'before the characters "^. $() * +? {\".

Note that no escape characters are required in square brackets.

two。 Regular expression validation controls the input character type of the text box

1. You can only enter numbers and English:

two。 You can only enter numbers:

3. You can only enter full-width:

4. Those who can only enter Chinese characters:

3. A popular illustration of the application of regular expressions

*

/ / check whether it is made up of numbers.

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

^ means that the character that starts with it matches the rule immediately following ^.

$means that the character that starts with it matches the rule immediately before $.

The content in [] is an optional character set

[0-9] indicates that the required character range is between 0-9.

{1 # 20} means that the length of the numeric string is legally 1 to 20, that is, the number of occurrence of the characters in [0-9] ranges from 1 to 20.

The paired use of / ^ and $/ should indicate a rule that requires the entire string to exactly match the definition, rather than just one substring in the string.

*

/ / check login: you can only enter 5-20 characters that start with a letter, can be numbered, "_", "." String of

/ ^ [a-zA-Z] {1} ([a-zA-Z0-9] | [. _]) {4pm 19} $/

^ [a-zA-Z] {1} indicates that the first character is required to be a letter.

([a-zA-Z0-9] | [. _]) {4jue 19} represents a string of 4 to 9 bits in length starting from the second bit (because it follows the previous expression) and requires uppercase and lowercase letters, numbers, or a special character set [. _].

*

/ / verify user name: only 1-30 strings that begin with letters can be entered

/ ^ [a-zA-Z] {1pc30} $/

*

/ / check password: only 6-20 letters, numbers and underscores can be entered

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

\ w: used to match alphabetic, numeric or underscore characters

*

/ / check ordinary telephone and fax numbers: can be "+" or start with a number, and can contain "-" and "".

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

\ d: used to match numbers from 0 to 9

"?" The metacharacter states that its leading object must appear zero or once in a row in the target object.

Strings that can be matched, such as: + 123-999999; + 123-999999; + 123 999999; + 123 999999, etc.

*

/ / verify URL

/ ^ http [s] {0http 1}:\ /\ /. + $/ or / ^ http [s] {0Magne1}:\ /. {1Magne1} $/ (indicates that the length of the url string is length ("https://") + n)"

\ /: represents the character "/".

. Represents a set of all characters

+ equals {1,}, which means 1 to positive infinity.

*

/ / verify pure Chinese characters / ^ [\ u4E00 -\ u9FA5] + $/ [\ u4E00 -\ u9FA5]: estimated to be the scope of the Chinese character set. The above expressions are all tested in the following javascript to pass the regular expression: (fill in the expression between / /)

Check string:

4. Application of rule table formula

"^\ integer $" / / non-negative integer (positive integer + 0)

"^ [0-9] * [1-9] [0-9] * $" / / positive integer

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

"^-[0-9] * [1-9] [0-9] * $" / / negative integer

"^ -?\ During $" / / Integer

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

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

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

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

"^ (-?\ d +) (\.\ d +)? $" / / floating point number

"^ [A-Za-z] + $" / / A string of 26 letters

"^ [Amurz] + $" / / A string of 26 English letters in uppercase

A string of 26 lowercase letters consisting of "^ [amurz] + $" / /

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

A string of numbers, 26 letters, or underscores

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

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

/ ^ (d {2} | d {4})-(0 ([1-9] {1})) | (1 [1 | 2]))-([0-2] ([1-9] {1})) | (3 [0 | 1])) $/ year-month-day

/ ^ ((0 ([1-9] {1})) | (1 [1 | 2])) / ([0-2] ([1-9] {1})) | (3 [0 | 1])) / (d {2} | d {4}) $/ month / day / year

"^ ([wmere.] +) @ ([[0-9] {1Mague 3}. [0-9] {1pr 3}. [0-9] {1pr 3}.) | (([w -] +.)) ([a-zA-Z] {2jue 4} | [0-9] {1Mague 3}) (]?) $" / / Emil

"(dwells -)? (d {4} -? d {7} | d {3} -? d {8} | ^ d {7je 8}) (- d +)? / / phone number

"^ (d {1 1dd 2} | 1dd | 2 [0-4] d | 25 [0-5]). (d {1 IP 2} | 1dd | 2 [0-4] d | 25 [0-5]). (d {1 recorder 2} | 1dd | 2 [0-4] d | 25 [0-5]). (d {1pm 2} | 1dd | 2 [0-4] d | 25 [0-5])

Regular expression of ^ ([0-9A-F] {2}) (- [0-9A-F] {2}) {5} $/ / MAC address

^ [- +]?\ d + (\.\ d +)? $/ / value type regular expression

5.javascript regular expression test

/ / verify whether it is composed entirely of numbers function isDigit (s) {var patrn=/ ^ [0-9] {1 patrn.exec 20} $/; if (! patrn.exec (s)) login} / / verify login name: only 5-20 logins can be entered, starting with a letter, with numbers, "_", "." The string function isRegisterUserName (s) {var patrn=/ ^ [a-zA-Z] {1} ([a-zA-Z0-9] | [. _]) {4 var patrn=/ 19} $/; if (! patrn.exec (s)) return falsereturn true} / / verify the user name: only 1-30 letters can be entered for function isTrueName (s) {var patrn=/ ^ [a-zA-Z] {1pm 30} $/ If (! patrn.exec (s)) return falsereturn true} / / check password: you can only enter 6-20 letters, numbers, and underscores function isPasswd (s) {var patrn=/ ^ (\ w) {6pm 20} $/ If (! patrn.exec (s)) return falsereturn true} / / verify ordinary telephone and fax numbers: you can start with "+" and contain "-" function isTel (s) {/ / var patrn=/ ^ [+] {0Mague 1} (\ d) {1Mague 3} []? ([-]? (\ d) {1cot 12}) + $/ Var patrn=/ ^ [+] {0jue 1} (\ d) {1JI 3} []? ([-]? ((\ d) | []) {1Jet 12}) + $/ If (! patrn.exec (s)) return falsereturn true} / / verify the mobile phone number: it must start with a number and may contain "-" function isMobil (s) {var patrn=/ ^ [+] {0jue 1} (\ d) {1prit 3} []? ([-]? (\ d) | []) {1m 12}) + $/ If (! patrn.exec (s)) return falsereturn true} / / check Postal Code function isPostalCode (s) {/ / var patrn=/ ^ [a-zA-Z0-9] {3 a-zA-Z0 12} $/; var patrn=/ ^ [a-zA-Z0-9] {3 a-zA-Z0 12} $/; if (! patrn.exec (s)) return falsereturn true} / / verify the search keyword function isSearch (s) {var patrn=/ ^ [^ `~! @ # $% ^ & * () + = |\\] [\]\ {\}: \'\,. /?] {1} [^ `~! @ $% ^ & () + = |\\] [\]\]\ {\}:;\'\,.] {0return falsereturn true 19} $/; if (! patrn.exec (s)) return falsereturn true} function isIP (s) / / by zergling {var patrn=/ ^ [0-9.] {1pm 20} $/ If (! patrn.exec (s)) return falsereturn true} / * FUNCTION: isBetween* PARAMETERS: val AS any value* lo AS Lower limit to check* hi AS Higher limit to Check* CALLS: NOTHING* RETURNS: TRUE if val is between lo and hi both inclusive Otherwise false.****/function isBetween (val, lo, hi) {if ((val)

< lo) || (val >

Hi) {return (false);} else {return (true) }} / * FUNCTION: isDate checks a valid date* PARAMETERS: theStr AS String* CALLS: isBetween IsInt* RETURNS: TRUE if theStr is a valid date otherwise false.****/function isDate (theStr) {var the1st = theStr.indexOf ('-') Var the2nd = theStr.lastIndexOf ('-'); if (the1st = = the2nd) {return (false);} else {var y = theStr.substring; var m = theStr.substring (the1st+1,the2nd); var d = theStr.substring (the2nd+1,theStr.length); var maxDays = 31 if (isInt (m) = = false | | isInt (d) = false | | isInt (y) = false) {return (false);} else if (y.length)

< 4) { return(false); }else if (!isBetween (m, 1, 12)) { return(false); }else if (m==4 || m==6 || m==9 || m==11) maxDays = 30;else if (m==2) {if (y % 4 >

0) maxDays = 28 return if (y% 100 = = 0 & & y% 400 > 0) maxDays = 28 return maxDays = 29;} if (isBetween (d, 1, maxDays) = = false) {return (false);} else {return (true) }} / * FUNCTION: isEuDate checks a valid date in British format* PARAMETERS: theStr AS String* CALLS: isBetween IsInt* RETURNS: TRUE if theStr is a valid date otherwise false.****/function isEuDate (theStr) {if (isBetween (theStr.length, 8,10) = = false) {return (false) } else {var the1st = theStr.indexOf ('/'); var the2nd = theStr.lastIndexOf ('/'); if (the1st = = the2nd) {return (false);} else {var m = theStr.substring (the1st+1,the2nd); var d = theStr.substring; var y = theStr.substring (the2nd+1,theStr.length); var maxDays = 31 if (isInt (m) = false | isInt (d) = false | | isInt (y) = = false) {return (false);} else if (y.length)

< 4) { return(false); }else if (isBetween (m, 1, 12) == false) { return(false); }else if (m==4 || m==6 || m==9 || m==11) maxDays = 30;else if (m==2) {if (y % 4 >

0) maxDays = 28 return if (y% 100 = = 0 & & y% 400 > 0) maxDays = 28 return maxDays = 29;} if (isBetween (d, 1, maxDays) = = false) {return (false);} else {return (true) } / * * FUNCTION: Compare Date! Which is the latestbands * PARAMETERS: lessDate,moreDate AS String* CALLS: isDate,isBetween* RETURNS: TRUE if lessDateDate2) {return (false);} return (true) } / * FUNCTION isEmpty checks if the parameter is empty or null* PARAMETER str AS String* * * / function isEmpty (str) {if ((str==null) | | (str.length==0)) return true Else return (false) } / * FUNCTION: isInt* PARAMETER: theStr AS String * RETURNS: TRUE if the passed parameter is an integer Otherwise FALSE* CALLS: isDigit****/function isInt (theStr) {var flag = true If (isEmpty (theStr)) {flag=false;} else {for (var iTuno; I decLen) return (false); else if (! isInt (intPart) | |! isInt (decPart)) return (false); else if (isEmpty (decPart)) return (false); else return (true) }} / * FUNCTION: isEmail* PARAMETER: String (Email Address) * RETURNS: TRUE if the String is a valid Email address* FALSE if the passed string is not a valid Email Address* EMAIL FORMAT: AnyName@EmailServer e.g Webmaster@hotmail.com* @ sign can appear only once in the email address.****/function isEmail (theStr) {var atIndex = theStr.indexOf ('@') Var dotIndex = theStr.indexOf ('.', atIndex); var flag = true;theSub = theStr.substring (0, dotIndex+1) if ((atIndex)

< 1)||(atIndex != theStr.lastIndexOf('@'))||(dotIndex < atIndex + 2)||(theStr.length Document to open in the new windowhite ->

Height of the new windowwide-> Width of the new windowbars-> 1-Scroll bars = YES 0-Scroll Bars = NOresize-> 1-Resizable = YES 0-Resizable = NO* CALLS: NONE* RETURNS: New window instance**** * / function newWindow (doc Hite, wide, bars, resize) {var winNew= "_ blank" Var opt= "toolbar=0,location=0,directories=0,status=0,menubar=0,"; opt+= ("scrollbars=" + bars+ ","); opt+= ("resizable=" + resize+ "); opt+= (" width= "+ wide+", "); opt+= (" height= "+ hite); winHandle=window.open (doc,winNew,opt); return } / * FUNCTION: DecimalFormat* PARAMETERS: paramValue-> Field value* CALLS: NONE* RETURNS: Formated string* * / function DecimalFormat (paramValue) {var intPart = parseInt (paramValue) Var decPart = parseFloat (paramValue)-intPart;str = ""; if ((decPart = = 0) | | (decPart = = null) str + = (intPart + ".00"); else str + = (intPart + decPart); return (str);}

"^\\ integer $" / / non-negative integer (positive integer + 0)

"^ [0-9] * [1-9] [0-9] * $" / / positive integer

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

"^-[0-9] * [1-9] [0-9] * $" / / negative integer

"^ -?\\ During $" / / Integer

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

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

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

"^ (- (([0-9] +\. [0-9] * [1-9] [0-9] *) | ([0-9] * [1-9] [0-9] *. [0-9] +) | ([0-9] * [1-9] [0-9] *)) $" / / negative floating point number

"^ (-?\\ d +) (\.\\ d +)? $" / / floating point number

"^ [A-Za-z] + $" / / A string of 26 letters

"^ [Amurz] + $" / / A string of 26 English letters in uppercase

A string of 26 lowercase letters consisting of "^ [amurz] + $" / /

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

A string of numbers, 26 letters, or underscores.

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

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

This is the end of this article on "what is the basic grammar of regular expressions?". I hope the above content can be helpful to you, so that you can learn more knowledge. If you think the article is good, please share it for more people to see.

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