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RegEx for subdomain with varying number

Using Javascript RegExp, I'm trying to match URL like the following:
http://sub.domain.com/
http://sub1.domain.com/
http://sub100.domain.com/
I tried the following regex, which isn't working - not sure what I'm doing wrong ?
^http\:\/\/sub\d*\.domain\.com\/$
EDIT: fixed copy & paste typo
Update: For some reason, document.location.href doesn't match the regex - even though examples below (also on regex101.com) do work as expected. My workaround for now - I just match any subdomain.
..any help is much appreciated!

i dont understand How you can compare a grape with a mango
here is the corrected regex :
/^http\:\/\/subs\d*\.app\.clicktale\.com\/$/.test("http://subs14.app.clicktale.com/");
run this command in your console, right now.
you will get true , if you use search then you will get 0 because the index of your match is 0

Well the sub-domains you showed have the token "sub", but your REGEX is looking for "subs".
Also, no need to escape colons.
You don't say whether you wish to test for a match or actually capture the sub-domain. I'll assume the latter:
var match = "http://foo.bar.com".match(/https?:\/\/(([^.]+)\.)?/);
alert(match[2]); //"foo"

regex replace all backward slashes before '\?'

I have a string such as
'frontend\less\defaults\layout.css?file=\foo'
I want a regex that replaces it with
'frontend/less/defaults/layout.css?file=\foo'
I tried /\\/g, but it keeps matching stuff after a \?, which I want to avoid somehow

Following will work, use a lookahead in your regexp:
var myString="path\\to\\file.php?query=\\something"
var r=(/\?/g.test(myString))?/(\\)(?=.+[\?])/ig:/\\/ig;
.replace(r,"/")

You can do this with String.replace, with a replacement function:
str.replace(/^([^?]*)/, function (_, $1) {
return $1.replace(/\\/g, '/');
});
This will work regardless of whether the query string exists or not.
Explanation
/^([^?]*)/
([^?]*) will match and capture everything before ? (if any).
I assume the URL is valid, so there is no validation done here.
(Thanks to #Pumbaa80 for the suggestion. There is no need to match the query string part if it is going to stay the same after the replacement)

Unless you know the number of \'s in advance, I doubt you can do this with a comprehensible regex. I would:
split the string in two parts: the part before the ?, and after it
use your regex on the first part
put the two strings back together.

Need help in regex pattern

i have this Regex pattern
\=[a-zA-Z\.\:\[\]_\(\)\&\$\%#\-\#\!0-9;=\?/\+\xBF\~]+[?\s+|?>]
and i have this HTML
1.esc#xyz.com
2.johnross#zys.com
3.johnross#wen.com
Here the problem is,
I need to avoid first and second as it has white space as well and it is valid attributes.
But only the third one is working as it does't has white spaces.
means nothing should be selected with the above pattern.
here is direct link to test
http://regexr.com?31r61
Please help!
Thanks,

EDIT:
If you just want to match unquoted attributes, this should work:
[<\s]+[\w]+(=[^\"][^\s>]*)
Kind of inelegant but let me know if that does what you want.
Which pattern are you trying to match? All three? And if so, which portion? The subject or the email? If you're just trying to match the subject, try using this as the pattern to match:
\=\"mailto:[^?]*\?subject=([^\"]*)\"\>
That will return a match where the group is the subject itself.

That is a wicked character class....
why don't you try something a bit more reasonable. Try this...
\=".*?(?<!\\)"
that will match anything in the parenthesis after href if that's what you're trying to get. If you're looking for more than that, this regex can easily by modified.

What's wrong with this regular expression to find URLs?

I'm working on a JavaScript to extract a URL from a Google search URL, like so:
http://www.google.com/search?client=safari&rls=en&q=thisisthepartiwanttofind.org&ie=UTF-8&oe=UTF-8
Right now, my code looks like this:
var checkForURL = /[\w\d](.org)/i;
var findTheURL = checkForURL.exec(theURL);
I've ran this through a couple regex testers and it seems to work, but in practice the string I get returned looks like this:
thisisthepartiwanttofind.org,.org
So where's that trailing ,.org coming from?
I know my pattern isn't super robust but please don't suggest better patterns to use. I'd really just like advice on what in particular I did wrong with this one. Thanks!

Remove the parentheses in the regex if you do not process the .org (unlikely since it is a literal). As per #Mark comment, add a + to match one or more characters of the class [\w\d]. Also, I would escape the dot:
var checkForURL = /[\w\d]+\.org/i;

What you're actually getting is an array of 2 results, the first being the whole match, the second - the group you defined by using parens (.org).
Compare with:
/([\w\d]+)\.org/.exec('thisistheurl.org')
→ ["thisistheurl.org", "thisistheurl"]
/[\w\d]+\.org/.exec('thisistheurl.org')
→ ["thisistheurl.org"]
/([\w\d]+)(\.org)/.exec('thisistheurl.org')
→ ["thisistheurl.org", "thisistheurl", ".org"]
The result of an .exec of a JS regex is an Array of strings, the first being the whole match and the subsequent representing groups that you defined by using parens. If there are no parens in the regex, there will only be one element in this array - the whole match.

You should escape .(DOT) in (.org) regex group or it matches any character. So your regex would become:
/[\w\d]+(\.org)/
To match the url in your example you can use something like this:
https?://([0-9a-zA-Z_.?=&\-]+/?)+
or something more accurate like this (you should choose the right regex according to your needs):
^https?://([0-9a-zA-Z_\-]+\.)+(com|org|net|WhatEverYouWant)(/[0-9a-zA-Z_\-?=&.]+)$

Regex to match part of a string

Regex fun again...
Take for example http://something.com/en/page
I want to test for an exact match on /en/ including the forward slashes, otherwise it could match 'en' from other parts of the string.
I'm sure this is easy, for someone other than me!
EDIT:
I'm using it for a string.match() in javascript

Well it really depends on what programming language will be executing the regex, but the actual regex is simply
/en/
For .Net the following code works properly:
string url = "http://something.com/en/page";
bool MatchFound = Regex.Match(url, "/en/").Success;
Here is the JavaScript version:
var url = 'http://something.com/en/page';
if (url.match(/\/en\//)) {
alert('match found');
}
else {
alert('no match');
}
DUH
Thank you to Welbog and Chris Ballance to making what should have been the most obvious point. This does not require Regular Expressions to solve. It simply is a contains statement. Regex should only be used where it is needed and that should have been my first consideration and not the last.

If you're trying to match /en/ specifically, you don't need a regular expression at all. Just use your language's equivalent of contains to test for that substring.
If you're trying to match any two-letter part of the URL between two slashes, you need an expression like this:
/../
If you want to capture the two-letter code, enclose the periods in parentheses:
/(..)/
Depending on your language, you may need to escape the slashes:
\/..\/
\/(..)\/
And if you want to make sure you match letters instead of any character (including numbers and symbols), you might want to use an expression like this instead:
/[a-z]{2}/
Which will be recognized by most regex variations.
Again, you can escape the slashes and add a capturing group this way:
\/([a-z]{2})\/
And if you don't need to escape them:
/([a-z]{2})/
This expression will match any string in the form /xy/ where x and y are letters. So it will match /en/, /fr/, /de/, etc.
In JavaScript, you'll need the escaped version: \/([a-z]{2})\/.

You may need to escape the forward-slashes...
/\/en\//

Any reason /en/ would not work?

/\/en\// or perhaps /http\w*:\/\/[^\/]*\/en\//

You don't need a regex for this:
location.pathname.substr(0, 4) === "/en/"
Of course, if you insist on using a regex, use this:
/^\/en\//.test(location.pathname)