Reverse pre-search in regular expressions __ regular expressions

These days in a regular expression to do a small program, you need to replace some of the special strings in the content. The occurrence of these strings is regular, that is, there will always be a specific content on the left, but not the right. So naturally the idea of a reverse search.

In previous applications, most of the applications were in forward search. That is, there is a specific content qualification on the right side of the lookup content, such as the following example:

var str3 = ' Cpu:intel Core2 5200; Memory:2g;os:ubuntu 9.04 '; var reg3 =/memory/:/s+ (. * (? =/;os/:))/gim; Str3.match (REG3); alert (regexp.$1);//The result is 2G.

(. * (? =/;os/:) is a typical forward lookup, only the right content is "; OS:" will be matched to.

But now to achieve the effect, the left side of the content is fixed, not to the right. However, JavaScript does not support reverse lookup. I believe that a careful friend has found that the above example has reached this goal (the previous memory/:/s+ defines the left side of the content). An example is given below:

Program purpose to remove the domain name var str in the image path = ' '; var reg1 =/(/

So is there any reverse pre-search? The answer is yes, but the reality is brutal. I looked up some information, which mentioned the reverse pre-search in the form of <= or <!. As a guide. Unfortunately, JavaScript is not supported and has been supported in a later version of Java, so the following test program (JRE1.6.0_03) is written:

Import Java.util.regex.Matcher; Import Java.util.regex.Pattern; public class Regexptest {public static void main (string[] args) {Pattern p = pattern.compile ("() <=//

The program itself should have no problems, but the results of the operation:

Exception in thread ' main ' java.util.regex.patternsyntaxexception:look-behind group does not have an obvious maximum Th near Index 27
((? <=/

I google for a long time, the end of the only result is to change the way the wording. Hope to see this article friend, if already realized this kind of effect, must leave a message hesitate enlighten.

Also, when I look at the document, I see it: the regular expression of the boot, which says "match does not store", baffled. Feel or code to the reality, write a look at:

var str2 = ' client name '; var REG2 =/(client name (?: Said)?) /; Str2.match (REG2); alert (regexp.$1); Client name alert (regexp.$2); empty string//Not used?: REG2 =/(client name (called)?) /; Str2.match (REG2); alert (regexp.$1); Client name alert (regexp.$2); Said

Agile development Theory says: Code is the best document. Gave me an excuse, hehe.