Regular Expressions in javascript and php

Source: Internet
Author: User
Tags preg
Regular: varsubStrstrreplace (regstr, & 039; & 039;); returns the replaced character seek without changing the original string; if you do not need regular expressions, you can only Replace the first matched character; varsubStrstrmatch (reg); returns the matched string.

Regular Expression:

Var subStr = str. replace (reg/str, ''); returns the replaced character seek without changing the original string; if regular expressions are not used, only the first matched character can be replaced;


Var subStr = str. match (reg); returns the matched string. If no global match is specified, only match the first character, which is generally used with the regular expression;


Var bool = reg. test (str) ;==>Check whether the regular expression matches the Regular Expression in str.,

Var Int= Str. search (reg/str );Returns the first occurrence location of the reg/str to be searched.,No response found-1;Search for small strings in large strings;It can be used with the match, but global match does not work, because only the position of the first matched character is returned;


Var subStr = str. charAt (int)Returns a character at the specified position;


Var subStr = str. sbustring (start, [end]);Does not include the end bit;

Var subStr = str. substr (start, length );


Var arr = str. split ('delimiter'); The default value is comma;


Regular-compatibleStringFunction;

* *** The most important use of regular-compatible str functions and regular expressions is that Fuzzy Matching and global matching can be used. If you only search for a single string, you do not need to use regular expressions;


1 str. split (preg) ==> separates str into an Array Based on the Content matched by a regular expression. Note that if a subexpression exists, in addition to the overall regular expression, it is also separated by a subexpression, when using the split function, it is best not to use a regular expression;

Test code:


Var str = 'aabbccddaabbccdd ';

Var preg =/aa/g;

Var res = str. split (preg );

// Alert (res. constructor); // function Array;


2Str. Match (preg) =>Returns an array.;

Test code:


Var str = 'aabbccddaabbccdd ';

Var preg =/aa/g;

Var a = str. match (preg );

// Alert (a. constructor); // function Array;

// Alert (a. length); // 2;

// Alert (a); // aa, aa


3 str. search


Var str = 'aabbccddaabbccdd ';

Var preg =/aa/g;

Var res = str. search (preg );

// Alert (res. constructor); // function Number; global match does not work;

// Alert (res); // 0: The first matched position is not found.-1 is returned;


4str. replace;


Var str = 'aabbccddaabbccdd ';

Var preg =/aa/g;

Var res = str. replace (preg ,'*');

Alert (res); // * bbccdd;

// Search for aabbcc and replace bb *

Var res1 = str. replace (preg, '$1*$2 ');

Alert (res1); // aa * ccddaa * ccdd;


Regular Functions;

1 test;

VarBool = preg. test (str );

2 exec

Preg.exe c (str); // jsThe most powerful regular functions;

Demo:

Var str = 'aabbccddaabbccdd ';

Var preg =/aa (bb)/g;

Var reselect preg.exe c (str );

// Alert (res); // aabb, aa; // The returned result is an array. The res [0] of this array is the whole of the regular match, followed by a matched subexpression. When fuzzy match is performed on a string, the returned results can be used to determine the exact match;

// In js, everything is an object. The returned array contains two attributes: index and input;

// Alert (res. index); // 0 returns the offset;

// Alert (res. input); // return str for aabbccddaabbccdd;

// Var reselect preg.exe c (str );

// Var res1‑preg.exe c (str );

// Alert (res. index); // 0 // This is similar to the function mysql_fetch_assoc (res) used to obtain mysql resources in php. You can use a while statement to print all globally matched information;

// Alert (res1.index); // 8

Finally, let's try again.;Retrieve all information;


Var str = 'aabbccddaabbccdd ';

Var preg =/aa (bb)/g;


While(res=preg.exe c (str )){


For (key in res ){

Document. write (key + '=' + res [key] +'
');

}

}

0 = aabb

1 = bb

Index = 0

Input = aabbccddaabbccdd

0 = aabb

1 = bb

Index = 8

Input = aabbccddaabbccdd


Case-sensitive Regular Expressions;

I. case insensitive;

Js regular object RegExp,Includes some attributes,Such as the matching mode I m g s;

Demo var reg =/^ \S+ | \ S + $/Img; reg. source = return^ \S+ | \ S + $

Reg. Global =>Returns true.==> (Because the created reg object specifies global matching)

/^ \S+ | \ S + $/g ==>Space at the beginning and end of the row;

/^ \ S $/mg; ==> matches empty rows;


| Or note:/a | B | c/=/[abc]/;


The first usage of square brackets [] is the first usage ==> or

The second use [a-z] range => indicates one in the azimuth;

Method 3 ^ put in square brackets [^] to indicate inverse;


[\ U4e00-\ u9fa5] ==> match Chinese characters;

To match a single Chinese character, you can check the Chinese unicode hexadecimal encoding;

^Beginning of Line

$ End of line


\ B: the boundary character of the word must start or end with a space or a comma;

\ B word non-Boundary

[^]Except XXX;

.Represents any character

+Representative{1,N}Same as the preceding characters.

\ DDigital

\ D [^ 0-9] is opposite to \ d

\W[0-9a-zA-Z _] word

\W [^ 0-9a-zA-Z _] Note/[a-zA-Z _]/==/ [a-z]/ig;

\ S space

\S Characters except spaces;

\ SS matches all non-null characters


{N, m}

{N ,}

{, M}

{N}

{1 ,}=> +

{0 ,}=> *

{0, 1 }=>Appears0Time or once


Multiline Mode M(Each line of a large string is treated as a start and end. If you do not use the multiline mode, no matter how many lines there are, the positive string has only one start and one end.);

Question:

Replace the character at the end of each line #;


Single Row Mode(In php, if the regular expression match mode is set to single-line mode, that is, the (point). metacharacters represent any character, including line breaks;)--Purpose,If a line break exists between the characters to be matched,The dot metacharacters cannot be matched, resulting in no matching results.

In js, the single-line mode is not supported. You can use a pair of negative characters to replace the single-line mode;


Pre-query (assertion) ==> pre-query characters are not included in the results,


Backward pre-query (assertion) (pre-judge whether the previous value is a set value) syntax==>(? = Xxx );

Or (pre-determine whether the previous value is not a specific value) syntax => (?! Xxx );



1 // search for the root of a word ending with ing/\ B \ w +? (? = Ing \ B)/ig; // the word itself contains ing, but the returned result is the part after ing;

Var preg =/\ bwin (? = Xp \ B) xp \ B /;//To include the preference Section,Add the pre-check content after the pre-check;


2 // search for words starting with win and not win95;

Var str = 'winxp winstart win95 win2003 ';

Var preg =/\ bwin (?! 95) \ w +? \ B/ig;

Var str1 = str. match (preg );

Alert (str1); // winxp winstart win2003


3 // find the root of the word starting with "un":

VarStr = 'Happy unknown happy undo ';

Var preg =/\ B (? = Un) \ w +? \ B/gi;

Var str1 = str. match (preg );

Alert (str1); // happy known do


Forward pre-check (assertion): (js is not supported currently) php (supported );

Reverse reference subexpression:

(? : Pattern) matches pattern but does not get the matching result. That is to say, this is a non-get match and is not stored for future use;

Use \ 1, \ 2 \ 3... in the regular expression ........ \ N reference;

$1, $2 ,..... $ N reference;


Perfect getByClass

Function getByClass (oParent,ClassName){

Var aEle = oParent. getElementsByTgeName ('*');

VarAResult = [];

Var reg =/\ B + className \ B +/

Var I = 0;

For (I; I

If (reg. test (aEle [I]. className )){

AResult. push (aEle [I]);

}

}

Return aResult;

}






PhpRegular;The regular expression syntax of php is almost the same as that of js, but the regular expression functions are different.


// Php regular functions;

Replace the array with regular expressions;

1: array preg_grep (string $ pattern, array $ input [, int $ flags = 0]);

The third optional parameter $ flag has only one value, PREG_GREP_INVERT. If this parameter is specified, no matching array elements are returned (I .e., inverse );


Regular Expression matching;

2 int preg_match (string $ pattern, string $ subject [, array & $ matches])

The third optional parameter stores the matched string (one-dimensional array). It is best not to use the next two parameters. If 4th optional parameters are used, the number of digits of the array increases;

Return value. If the matching succeeds, 1 is returned. If no matching result is returned, 0 is returned;


3int preg_match_all (string $ pattern, string $ subject [, array & $ matches]);


Parameters and usage are the same as preg_match;

Return value, which matches the number of times matched; if no match is returned, 0 is returned;


4. Regular Expression replacement;

Mixed preg_replace (mixed $ pattern, mixed $ replacement, mixed $ subject [, int $ limit =-1)

This function is replaced globally by default (-1). If you do not want to replace all functions, you can specify the number of replacement times for the fourth optional parameter;


5. Regular Segmentation

Array preg_split (string $ pattern, string $ subject [, int $ limit =-1]);

This function returns an array. The fourth optional parameter specifies the maximum length of the array to be returned (this parameter can be used to segment the string randomly );


6. Escape special characters;

String preg_quote (string $ str [, string $ delimiter = NULL]);

This function adds a backslash to the special characters passed in the $ strcan parameter that have special meanings in the real world. The second optional parameter can be used to specify any character to be escaped; this function can be used with the previous regular functions to exert greater power;

Demo1:

$ Keywords = '$40 for a g3/100 ';

$ Keywords = preg_quote ($ keywords ,'/');

Echo $ keywords; // returns \40 40 for a g3 \/400


Demo2:

$ Textbody = "This book is * very * difficult to find .";

$ Word = "* very *";

$ Textbody = preg_replace ("/". preg_quote ($ word )."/",

"". $ Word ."",

$ Textbody );


Related Article

E-Commerce Solutions

Leverage the same tools powering the Alibaba Ecosystem

Learn more >

Apsara Conference 2019

The Rise of Data Intelligence, September 25th - 27th, Hangzhou, China

Learn more >

Alibaba Cloud Free Trial

Learn and experience the power of Alibaba Cloud with a free trial worth $300-1200 USD

Learn more >

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.