Develop Reference

How would I write a Regular Expression to capture the value between Last Slash and Query String?

Problem:
Extract image file name from CDN address similar to the following:
https://cdnstorage.api.com/v0/b/my-app.com/o/photo%2FB%_2.jpeg?alt=media&token=4e32-a1a2-c48e6c91a2ba
Two-stage Solution:
I am using two regular expressions to retrieve the file name:
var postLastSlashRegEx = /[^\/]+$/,
preQueryRegEx = /^([^?]+)/;
var fileFromURL = urlString.match(postLastSlashRegEx)[0].match(preQueryRegEx)[0];
// fileFromURL = "photo%2FB%_2.jpeg"
Question:
Is there a way I can combine both regular expressions?
I've tried using capture groups, but haven't been able to produce a working solution.

From my comment
You can use a lookahead to find the "?" and use [^/] to match any non-slash characters.
/[^/]+(?=\?)/
To remove the dependency on the URL needing a "?", you can make the lookahead match a question mark or the end of line indicator (represented by $), but make sure the first glob is non-greedy.
/[^/]+?(?=\?|$)/

You don't have to use regex, you can just use split and substr.
var str = "https://cdnstorage.api.com/v0/b/my-app.com/o/photo%2FB%_2.jpeg?alt=media&token=4e32-a1a2-c48e6c91a2ba".split("?")[0];
var fileName = temp.substr(temp.lastIndexOf('/')+1);
but if regex is important to you, then:
str.match(/[^?]*\/([^?]+)/)[1]

The code using the substring method would look like the following -
var fileFromURL = urlString.substring(urlString.lastIndexOf('/') + 1, urlString.lastIndexOf('?'))

How to get youku video id from url by regex?

I need to get youku video id from url by regex, for example:
http://v.youku.com/v_show/id_XNTg3OTc3MzY4.html
I only need XNTg3OTc3MzY4 to keep in a variable.
How can I write it in function below
var youkuEmbed = "[[*supplier-video]]";
var youkuUrl = youkuEmbed.match(/http://v\.youku\.com/v_show/id_(\w+)\.html/);
I tried this but it didn't work.
Thanks!

You can use a simple regex like this:
id_(\w+)
Working demo
The idea is to match the _id and the capture all the alphanumeric strings.
MATCH 1
1. [29-42] `XNTg3OTc3MzY4`
If you go the Code Generator section you can get the code. However, you can use something like this:
var myString = 'http://v.youku.com/v_show/id_XNTg3OTc3MzY4.html';
var myRegexp = /id_(\w+)/;
var match = myRegexp.exec(myString);
alert(match[1]);
//Shows: XNTg3OTc3MzY4

You can use this regex:
http://v\.youku\.com/v_show/id_(\w+)\.html
Your match is in the first capturing group.
Here is a regex demo.

Id the id always follows id_, you could possibly split the string.
'http://v.youku.com/v_show/id_XNTg3OTc3MzY4.html'.split(/.*id_|\./)[1]
//=> 'XNTg3OTc3MzY4'
For this specific string, you could just do.
'http://youku.com/id_XNTg30Tc3MzY4.html'.split(/id_|\./)[2]
//=> 'XNTg3OTc3MzY4'

It looks like you need to escape all the slashes because that's the delimiter for the regex itself:
var youkuUrl = youkuEmbed.match(/http:\/\/v\.youku\.com\/v_show\/id_(\w+)\.html/);
Then use the first capture group, as Unihedron stated.

Matching everything after first pipe character in Javascript RegEx

I have this string:
"http://www.yahoo.com/abc/123|X|Y|Z"
I need to get everything after the first pipe with a regex. So I would want to be left with this string:
"X|Y|Z"
How do I do this in JavaScript?

Using a simpler regex /\|(.*)/
var str = "http://www.yahoo.com/abc/123|X|Y|Z";
var aryMatches = str.match(/\|(.*)/);
// aryMatches[1] will have your results
regex explaination

Converting my comment to an answer:
Shockingly, regexes are not the answer to everything.
> xkcd
Try this:
str.split("|").slice(1).join("|");
This splits your string on pipe characters, slices off the first item, then joins the rest with pipes again.

First group contains the expected characters,
^.*?\|(.*)$
DEMO

You can use this regex:
/^[^|]*\|(.*)/
And use matched group #1 for your match.

Forget the splitting and splicing, just use a substring
var str = "http://www.yahoo.com/abc/123|X|Y|Z";
str.substr(str.indexOf("|") + 1);

Is it possible to cut off the beginning of a string using regex?

I have a string which contains a path, such as
/foo/bar/baz/hello/world/bla.html
Now, I'd like to get everything from the second-last /, i.e. the result shall be
/world/bla.html
Is this possible using a regex? If so, how?
My current solution is to split the string into an array, and join its last two members again, but I'm sure that there is a better solution than this.

For example:
> '/foo/bar/baz/hello/world/bla.html'.replace(/.*(\/.*\/.*)/, "$1")
/world/bla.html

You can also do
str.split(/(?=\/)/g).slice(-2).join('')

> '/foo/bar/baz/hello/world/bla.html'.match(/(?:\/[^/]+){2}$/)[0]
"/world/bla.html"
Without regular expression:
> var s = '/foo/bar/baz/hello/world/bla.html';
> s.substr(s.lastIndexOf('/', s.lastIndexOf('/')-1))
"/world/bla.html"

I think this will work:
var str = "/foo/bar/baz/hello/world/bla.html";
alert( str.replace( /^.*?(\/[^/]*(?:\/[^/]*)?)$/, "$1") );
This will allow for there being possibly only one last part (like, "foo/bar").

You can use /(\/[^\/]*){2}$/ which selects a slash and some content twice followed by the end of the string.
See this regexplained.

Regex to get a specific query string variable in a URL

I have a URL like
server/area/controller/action/4/?param=2"
in which the server can be
http://localhost/abc
https://test.abc.com
https://abc.om
I want to get the first character after "action/" which is 4 in the above URL, with a regex. Is it possible with regex in js, or is there any way?

Use regex \d+(?=\/\?)
var url = "server/area/controller/action/4/?param=2";
var param = url.match(/\d+(?=\/\?)/);
Test code here.

Using this regex in JavaScript:
action/(.)
Allows you to access the first matching group, which will contain the first character after action/ -- see the examples at JSFiddle

This way splits the URL on the / characters and extracts the last but one element
var url = "server/area/controller/action/4/?param=2".split ('/').slice (-2,-1)[0];