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return substring match

I am trying to get just a part of a string with a regex
this is the string i am testing
class1 container _box _box_CEC493
the string is a series of classes applied to an element.
what i would like to get is just CEC493 which changes since the regex will be applied to a bunch of different elements (therefore string like the one above)
the regex i am using now is
/\s_box_([0-9a-zA-Z]+)/
which returns
_box_CEC493, CEC493
How can i modify it in order to get just the second value (CEC493)?
Thank you

You could probably just split the string:
var str = "class1 container _box _box_CEC493";
var match = str.split('_').pop();
alert(match);
DEMO

The standard way regexes come back is like this:
[0]: Whole result
[1]: First parentheses capture group
etc
So the standard way that people access these is with result[1]. Does that cause any issues in your case?

[updated]
instead of selecting all characters, select until an unwanted character,, and since you are selecting from a number of classes, it is possible that you have the _box_.. class alone without a space before it, so don't use space at the beginning of your regex selector.
str.match(/_box_([^\s]*)/)[1]
jsfiddle

How to get data from string using Javascript Regex

I can't post the exact data i'm trying to extract but here's a basic scenario with the same outcome. I'm grabbing the body of a page and trying to extract a bit.ly link from it. So let's say for example, this is the chunk of data where i'm trying to grab the link from.
String:
http://bit.ly/Pq8AkS</div><div class="shareUnit"><div class="-cx-PRIVATE-fbTimelineExternalShareUnit__wrapper"><div><div class="-cx-PRIVATE-fbTimelineExternalShareUnit__root -cx-PRIVATE-fbTimelineExternalShareUnit__hasImage"><a class="-cx-PRIVATE-fbTimelineExternalShareUnit__video -cx-PRIVATE-fbTimelineExternalShareUnit__image -cx-PRIVATE-fbTimelineExternalShareUnit__content" ajaxify="/ajax/flash/expand_inline.php?target_div=uikk85_59&share_id=271663136271285&max_width=403&max_height=403&context=timelineSingle" rel="async" href="#" onclick="CSS.addClass(this, "-cx-PRIVATE-fbTimelineExternalShareUnit__loading");CSS.removeClass(this, "-cx-PRIVATE-fbTimelineExternalShareUnit__video");"><i class="-cx-PRIVATE-fbTimelineExternalShareUnit__play"></i><img class="img" src="http://external.ak.fbcdn.net/safe_image.php?d=AQDoyY7_wjAyUtX2&w=155&h=114&url=http%3A%2F%2Fi1.ytimg.com%2Fvi%2FDre21lBu2zU%2Fmqdefault.jpg" alt="" /></a>
Now, I can get what i'm looking for with the following code but the link isn't always going to be exactly 6 characters long. So this causes an issue...
Body = document.getElementsByTagName("body")[0].innerHTML;
regex = /2Fbit.ly%2F(.{6})&h/g;
Matches = regex.exec(Body);
Here's what I was orginally trying but the problem I have is that it grabs too much data. It's going all the way to the last "&h" in the string above instead of stopping at the first one it hits.
Body = document.getElementsByTagName("body")[0].innerHTML;
regex = /2Fbit.ly%2F(.*)&h/g;
Matches = regex.exec(Body);
So basically the main part of the string i'm trying to focus on is "%2Fbit.ly%2FPq8AkS&h" so that I can get the "Pq8AkS" out of it. When I use the (.*) it's grabbing everything between "%2F" and the very last "&h" in the large string above.

You should not be using a regex on HTML. Use DOM functions to get the desired link object, then get the href attribute from that, then you can use a regex on just the href.
By default .* is greedy meaning that it matches the most it can match and still find a match. If you want it to be non-greedy (match the least possible), you can use this .*? instead like this:
regex = /2Fbit.ly%2F(.*?)&h/;
I also don't think you want the g flag on the regex as there should only be one match in the right URL.
If you show the rest of your HTML, we could offer advice on finding the right link object rather than trying to match the entire body HTML.
FYI, another trick for a non-greedy match is to do something like this:
regex = /2Fbit.ly%2F([^&]*)&h/;
Which matches a series of characters that are not & followed by &h which accomplishes the same goal as long as & can't be in the matched sequence.

By default + and * are greedy and match as much as possible. You need a non-greedy match for your (.+). A quick search gives the solution as
? directly following a quantifier makes the quantifier non-greedy (makes it match minimum instead of maximum of the interval defined).
So try changing your regex= line to
regex = /2Fbit.ly%2F(.*?)&h/g;
Edit: #jfriend00's answer below is more complete.

Confused with Regex JS pattern

ok i do have this following data in my div
<div id="mydiv">
<!--
what is your present
<code>alert("this is my present");</code>
where?
<code>alert("here at my left hand");</code>
oh thank you! i love you!! hehe
<code>alert("welcome my honey ^^");</code>
-->
</div>
well what i need to do there is to get the all the scripts inside the <code> blocks and the html codes text nodes without removing the html comments inside. well its a homework given by my professor and i can't modify that div block..
I need to use regular expressions for this and this is what i did
var block = $.trim($("div#mydiv").html()).replace("<!--","").replace("-->","");
var htmlRegex = new RegExp(""); //I don't know what to do here
var codeRegex = new RegExp("^<code(*n)</code>$","igm");
var code = codeRegex.exec(block);
var html = "";
it really doesn't work... please don't give the exact answer.. please teach me.. thank you
I need to have the following blocks for the variable code
alert("this is my present");
alert("here at my left hand");
alert("welcome my honey ^^");
and this is the blocks i need for variable html
what is your present
where?
oh thank you! i love you!! hehe
my question is what is the regex pattern to get the results above?

Parsing HTML with a regular expression is not something you should do.
I'm sure your professor thinks he/she was really clever and that there's no way to access the DOM API and can wave a banner around and justify some minor corner-case for using regex to parse the DOM and that sometimes it's okay.
Well, no, it isn't. If you have complex code in there, what happens? Your regex breaks, and perhaps becomes a security exploit if this is ever in production.
So, here:
http://jsfiddle.net/zfp6D/
Walk the dom, get the nodeType 8 (comment) text value out of the node.
Invoke the HTML parser (that thing that browsers use to parse HTML, rather than regex, why you wouldn't use the HTML parser to parse HTML is totally beyond me, it's like saying "Yeah, I could nail in this nail with a hammer, but I think I'm going to just stomp on the nail with my foot until it goes in").
Find all the CODE elements in the newly parsed HTML.
Log them to console, or whatever you want to do with them.

First of all, you should be aware that because HTML is not a regular language, you cannot do generic parsing using regular expressions that will work for all valid inputs (generic nesting in particular cannot be expressed with regular expressions). Many parsers do use regular expressions to match individual tokens, but other algorithms need to be built around them
However, for a fixed input such as this, it's just a case of working through the structure you have (though it's still often easier to use different parsing methods than just regular expressions).
First lets get all the code:
var code = '', match = [];
var regex = new RegExp("<code>(.*?)</code>", "g");
while (match = regex.exec(content)) {
code += match[1] + "\n";
}
I assume content contains the content of the div that you've already extracted. Here the "g" flag says this is for "global" matching, so we can reuse the regex to find every match. The brackets indicate a capturing group, . means any character, * means repeated 0 or more times, and ? means "non-greedy" (see what happens without it to see what it does).
Now we can do a similar thing to get all the other bits, but this time the regex is slightly more complicated:
new RegExp("(<!--|</code>)(.*?)(-->|<code>)", "g")
Here | means "or". So this matches all the bits that start with either "start comment" or "end code" and end with "end comment" or "start code". Note also that we now have 3 sets of brackets, so the part we want to extract is match[2] (the second set).

You're doing a lot of unnecessary stuff. .html() gives you the inner contents as a string. You should be able to use regEx to grab exactly what you need from there. Also, try to stick with regEx literals (e.g. /^regexstring$/). You have to escape escape characters using new RegExp which gets really messy. You generally only want to use new RegExp when you need to put a string var into a regEx.
The match function of strings accepts regEx and returns a collection of every match when you add the global flag (e.g. /^regexstring$/g <-- note the 'g'). I would do something like this:
var block = $('#mydiv').html(), //you can set multiple vars in one statement w/commas
matches = block.match(/<code>[^<]*<\/code>/g);
//[^<]* <-- 0 or more characters that aren't '<' - google 'negative character class'
matches.join('_') //lazy way of avoiding a loop - join into a string with a safe character
.replace(/<\/*code>/g,'') //\/* 0 or more forward slashes
.split('_');//return the matches string back to array
//Now do what you want with matches. Eval (ew) or append in a script tag (ew).
//You have no control over the 'ew'. I just prefer data to scripts in strings

match text between two html custom tags but not other custom tags

I have something like the following;-
<--customMarker>Test1<--/customMarker>
<--customMarker key='myKEY'>Test2<--/customMarker>
<--customMarker>Test3 <--customInnerMarker>Test4<--/customInnerMarker> <--/customMarker>
I need to be able to replace text between the customMarker tags, I tried the following;-
str.replace(/<--customMarker>(.*?)<--\/customMarker>/g, 'item Replaced')
which works ok. I would like to also ignore custom inner tags and not match or replace them with text.
Also I need a separate expression to extract the value of the attribute key='myKEY' from the tag with Text2.
Many thanks
EDIT
actually I am trying to find things between comment tags but the comment tags were not displaying correctly so I had to remove the '!'. There's a unique situation that required comment tags... in anycase if anyone knows enough regex to help, it would be great. thank u.

In the end, I did something like the following (incase anyone else needs this. enjoy!!! But note: Word about town is that using regex with html tags is not ideal, so do your own research and make up your mind. For me, it had to be done this way, mostly bcos i wanted to, but also bcos it simplified the job in this instance);-
var retVal = str.replace(/<--customMarker>(.*?)<--\/customMarker>/g, function(token, match){
//question 1: I would like to also ignore custom inner tags and not match or replace them with text.
//answer:
var replacePattern = /<--customInnerMarker*?(.*?)<--\/customInnerMarker-->/g;
//remove inner tags from match
match = $.trim(match.replace(replacePattern, ''));
//replace and return what is left with a required value
return token.replace(match, objParams[match]);
//question 2: Also I need a separate expression to extract the value of the attribute key='myKEY' from the tag with Text2.
//answer
var attrPattern = /\w+\s*=\s*".*?"/g;
attrMatches = token.match(attrPattern);//returns a list of attributes as name/value pairs in an array
})

Can't you use <customMarker> instead? Then you can just use getElementsByTagName('customMarker') and get the inner text and child elements from it.

A regex merely matches an item. Once you have said match, it is up to you what you do with it. This is part of the problem most people have with using regular expressions, they try and combine the three different steps. The regex match is just the first step.
What you are asking for will not be possible with a single regex. You're going to need a mini state machine if you want to use regular expressions. That is, a logic wrapper around the matches such that it moves through each logical portion.
I would advise you look in the standard api for a prebuilt engine to parse html, rather than rolling your own. If you do need to do so, read the flex manual to get a basic understanding of how regular expressions work, and the state machines you build with them. The best example would be the section on matching multiline c comments.

Trying to remove trailing text

I having the following code. I want to extract the last text (hello64) from it.
<span class="qnNum" id="qn">4</span><span>.</span> hello64 ?*
I used the code below but it removes all the integers
questionText = questionText.replace(/<span\b.*?>/ig, "");
questionText=questionText.replace(/<\/span>/ig, "");
questionText = questionText.replace(/\d+/g,"");
questionText = questionText.replace("*","");
questionText = questionText.replace(". ",""); i want to remove the first integer, and need to keep the rest of the integers

It's the third line .replace(/\d+/g,"") which is replacing the integers. If you want to keep the integers, then don't replace \d+, because that matches one or more digits.
You could achieve most of that all on one line, by the way - there's no need to have multiple replaces there:
var questionText = questionText.replace(/((<span\b.*?>)|(<\/span>)|(\d+))/ig, "");
That would do the same as the first three lines of your code. (of course, you'd need to drop the |(\d+) as per the first part of the answer if you didn't want to get rid of the digits.
[EDIT]
Re your comment that you want to replace the first integer but not the subsequent ones:
The regex string to do this would depend very heavily on what the possible input looks like. The problem is that you've given us a bit of random HTML code; we don't know from that whether you're expecting it to always be in this precise format (ie a couple of spans with contents, followed by a bit at the end to keep). I'll assume that this is the case.
In this case, a much simpler regex for the whole thing would be to replace eveything within <span....</span> with blank:
var questionText = questionText.replace(/(<span\b.*?>.*?<\/span>)/ig, "");
This will eliminate the whole of the <span> tags plus their contents, but leave anything outside of them alone.
In the case of your example this would provide the desired effect, but as I say, it's hard to know if this will work for you in all cases without knowing more about your expected input.
In general it's considered difficult to parse arbitrary HTML code with regex. Regex is a contraction of "Regular Expressions", which is a way of saying that they are good at handling strings which have 'regular' syntax. Abitrary HTML is not a 'regular' syntax due to it's unlimited possible levels of nesting. What I'm trying to say here is that if you have anything more complex than the simple HTML snippets you've supplied, then you may be better off using a HTML parser to extract your data.

This will match the complete string and put the part after the last </span> till the next word boundary \b into the capturing group 1. You just need to replace then with the group 1, i.e. $1.
searched_string = string.replace(/^.*<\/span>\s*([A-Za-z0-9]+)\b.*$/, "$1");
The captured word can consist of [A-Za-z0-9]. If you want to have anything else there just add it into that group.