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JS regex to get domain name from an email [duplicate]

How can I extract only top-level and second-level domain from a URL using regex? I want to skip all lower level domains. Any ideas?

Here's my idea,
Match anything that isn't a dot, three times, from the end of the line using the $ anchor.
The last match from the end of the string should be optional to allow for .com.au or .co.nz type of domains.
Both the last and second last matches will only match 2-3 characters, so that it doesn't confuse it with a second-level domain name.
Regex:
[^.]*\.[^.]{2,3}(?:\.[^.]{2,3})?$
Demonstration:
Regex101 Example

Updated 2019
This is an old question, and the challenge here is a lot more complicated as we start adding new vanity TLDs and more ccTLD second level domains (e.g. .co.uk, .org.uk). So much so, that a regular expression is almost guaranteed to return false positives or negatives.
The only way to reliably get the primary host is to call out to a service that knows about them, like the Public Suffix List.
There are several open-source libraries out there that you can use, like psl, or you can write your own.
Usage for psl is quite intuitive. From their docs:
var psl = require('psl');
// Parse domain without subdomain
var parsed = psl.parse('google.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'google'
console.log(parsed.domain); // 'google.com'
console.log(parsed.subdomain); // null
// Parse domain with subdomain
var parsed = psl.parse('www.google.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'google'
console.log(parsed.domain); // 'google.com'
console.log(parsed.subdomain); // 'www'
// Parse domain with nested subdomains
var parsed = psl.parse('a.b.c.d.foo.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'foo'
console.log(parsed.domain); // 'foo.com'
console.log(parsed.subdomain); // 'a.b.c.d'
Old answer
You could use this:
(\w+\.\w+)$
Without more details (a sample file, the language you're using), it's hard to discern exactly whether this will work.
Example: http://regex101.com/r/wD8eP2

Also, you can likely do that with some expression similar to,
^(?:https?:\/\/)(?:w{3}\.)?.*?([^.\r\n\/]+\.)([^.\r\n\/]+\.[^.\r\n\/]{2,6}(?:\.[^.\r\n\/]{2,6})?).*$
and add as much as capturing groups that you want to capture the components of a URL.
Demo
If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.
RegEx Circuit
jex.im visualizes regular expressions:

For anyone using JavaScript and wanting a simple way to extract the top and second level domains, I ended up doing this:
'example.aus.com'.match(/\.\w{2,3}\b/g).join('')
This matches anything with a period followed by two or three characters and then a word boundary.
Here's some example outputs:
'example.aus.com' // .aus.com
'example.austin.com' // .austin.com
'example.aus.com/howdy' // .aus.com
'example.co.uk/howdy' // .co.uk
Some people might need something a bit cleverer, but this was enough for me with my particular dataset.
Edit
I've realised there are actually quite a few second-level domains which are longer than 3 characters (and allowed). So, again for simplicity, I just removed the character counting element of my regex:
'example.aus.com'.match(/\.\w*\b/g).join('')

Since TLDs now include things with more than three-characters like .wang and .travel, here's a regex that satisfies these new TLDs:
([^.\s]+\.[^.\s]+)$
Strategy: starting at the end of the string, look for one or more characters that aren't periods or whitespace, followed by a single period, followed by one or more characters that aren't periods or whitespace.
http://regexr.com/3bmb3

With capturing groups you can achieve some magix.
For example, consider the following javascript:
let hostname = 'test.something.else.be';
let domain = hostname.replace(/^.+\.([^\.]+\.[^\.]+)$/, '$1');
document.write(domain);
This will result in a string containing 'else.com'. This is because the regex itself will match the complete string and the capturing group will be mapped to $1. So it replaces the complete string 'test.something.else.com' with '$1' which is actually 'else.com'.
The regex isn't pretty and can probably be made more dynamic with things like {3} for defining how many levels deep you want to look for subdomains, but this is just an illustration.

if you want all specific Top Level Domain name then you can write regular expression like this:
[RegularExpression("^(https?:\\/\\/)?(([\\w]+)?\\.?(\\w+\\.((za|zappos|zara|zero|zip|zippo|zm|zone|zuerich|zw))))\\/?$", ErrorMessage = "Is not a valid fully-qualified URL.")]
You can also put more domain name from this link:
https://www.icann.org/resources/pages/tlds-2012-02-25-en

The following regex matches a domain with root and tld extractions (named capture groups) from a url or domain string:
(?:\w+:\/{2})?(?<cs_domain>(?<cs_domain_sub>(?:[\w\-]+\.)*?)(?<cs_domain_root>[\w\-]+(?<cs_domain_tld>(?:\.\w{2})?(?:\.\w{2,3}|\.xn-+\w+|\.site|\.club))))\|
It's hard to say if it is perfect, but it works on all the test data sets that I have put it against including .club, .xn-1234, .co.uk, and other odd endings. And it does it in 5556 steps against 40k chars of logs, so the efficiency seems reasonable too.

If you need to be more specific:
/\.(?:nl|se|no|es|milru|fr|es|uk|ca|de|jp|au|us|ch|it|io|org|com|net|int|edu|mil|arpa)/
Based on http://www.seobythesea.com/2006/01/googles-most-popular-and-least-popular-top-level-domains/

RegEx match only final domain name from any email address

I want to match only parent domain name from an email address, which might or might not have a subdomain.
So far I have tried this:
new RegExp(/.+#(:?.+\..+)/);
The results:
Input: abc#subdomain.maindomain.com
Output: ["abc#subdomain.domain.com", "subdomain.maindomain.com"]
Input: abc#maindomain.com
Output: ["abc#maindomain.com", "maindomain.com"]
I am interested in the second match (the group).
My objective is that in both cases, I want the group to match and give me only maindomain.com
Note: before the down vote, please note that neither have I been able to use existing answers, nor the question matches existing ones.

One simple regex you can use to get only the last 2 parts of the domain name is
/[^.]+\.[^.]$/
It matches a sequence of non-period characters, followed by period and another sequence of non-periods, all at the end of the string. This regex doesn't ensure that this domain name happens after a "#". If you want to make a regex that also does that, you could use lazy matching with "*?":
/#.*?([^.]+\.[^.])$/
However,I think that trying to do everything at once tends to make the make regexes more complicated and hard to read. In this problem I would prefer to do things in two steps: First check that the email has an "#" in it. Then you get the part after the "#" and pass it to the simple regex, which will extract the domain name.
One advantage of separating things is that some changes are easier. For example, if you want to make sure that your email only has a single "#" in it its very easy to do in a separate step but would be tricky to achieve in the "do everything" regex.

You can use this regex:
/#(?:[^.\s]+\.)*([^.\s]+\.[^.\s]+)$/gm
Use captured group #1 for your result.
It matches # followed by 0 or more instance of non-DOT text and a DOT i.e. (?:[^.\s]+\.)*.
Using ([^.\s]+\.[^.\s]+)$ it is matching and capturing last 2 components separated by a DOT.
RegEx Demo

With the following maindomain should always return the maindomain.com bit of the string.
var pattern = new RegExp(/(?:[\.#])(\w[\w-]*\w\.\w*)$/);
var str = "abc#subdomain.maindomain.com";
var maindomain = str.match(pattern)[1];
http://codepen.io/anon/pen/RRvWkr
EDIT: tweaked to disallow domains starting with a hyphen i.e - '-yahoo.com'

Matching Second part of MIME Content Type using RegExp

I've seen a number of examples on StackOverflow to get the "second" part of a MIME content type. What I'd like is, when provided with: text/html; charset=ISO-8859-1
I'd like to return just: html
The Regex I've seen thus far has been something like:
/[^text/]*$/
But in my testing, the matched result is just "ml"
I want whatever lies after the "text/" in the string, but for whatever reason all I'm getting is the last two letters. To be clear I consulted a number of other posts including:
Get second part of a string using RegEx
Which I thought would be exactly what I want, but my tests show that regex does not work.Any help would be much appreciated.
edit to broaden up the question. I'm trying to isolate part of the Content-Type returned in the jquery object.
var regex_content = /[^text/]([^;\s]+)/
var contentType = jqXHR.getResponseHeader("Content-Type");
alert(contentType.match(regex_content));
With the regex_content that someone else provided, html,tml is returned if the content type is text/html; charset=ISO-SOMENUMBERS. I'd like to ONLY have html be matched.

Your regex should be:
^text/([^;\s]+)
and capture the first group.
And since threre is a / in your regex, use the new RegExp() constructor:
var re = new RegExp("^text/([^;\\s]+)");

The main problem with your regex is that it ignores the characters t, e, x, and / individually and matches other characters. You want to match the group that follows the / and precedes the ;, so your regex would be
/(?:[^/]*\/)([^;]*)/
This has a non-capturing group ((?:[^/]*/)) match (and ignore) the characters up to the first /, then a capturing group (([^;]*)) to match and keep the text you want before the first ;.

Matching hostname on string when it has no protocol://?

I use this js code to match a hostname from a string:
url.match(/:\/\/(www\.)?(.[^/:]+)/);
This works when the url has protocol:// at the beginning. For example:
This works fine:
var url = "http://domain.com/page";
url.match(/:\/\/(www\.)?(.[^/:]+)/);
But this doesn't:
var url = "domain.com/page";
url.match(/:\/\/(www\.)?(.[^/:]+)/);
I have tried:
url.match(/(:\/\/)?(www\.)?(.[^/:]+)/);
And that matches fine the hostname when it doesn't contain protocol://, but when it does contains it it only returns the protocol and not the hostname.
How could I match the domain when it doesn't contains it?

I used this function from Steven Levithan, it parses urls quite decently.
Here's how you use this function
alert(parseUri("www.domain.com/foo").host)

OK before you have a brain meltdown from #xanatos answer here is a simple regex for basic needs. The other answers are more complete and handle more cases than this regex :
(?:(?:(?:\bhttps?|ftp)://)|^)([-A-Z0-9.]+)/
Group 1 will have your host name. URL parsing is a fragile thing to do with regexes. You were on the right track. You had two regexes that worked partially. I simply combined them.
Edit : I was tired yesterday night. Here is the regex for jscript
if (subject.match(/(?:(?:(?:\bhttps?|ftp):\/\/)|^)([\-a-z0-9.]+)\//i)) {
// Successful match
} else {
// Match attempt failed
}

This
var rx = /^(?:(?:ht|f)tp(?:s?)\:\/\/|~\/|\/)?(?:\w+:\w+#)?(?:(?:[-\w]+\.)+(?:com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum|travel|[a-z]{2}))(?::[\d]{1,5})?(?:(?:(?:\/(?:[-\w~!$+|.,=]|%[a-f\d]{2})+)+|\/)+|\?|#)?(?:(?:\?(?:[-\w~!$+|.,*:]|%[a-f\d{2}])+=?(?:[-\w~!$+|.,*:=]|%[a-f\d]{2})*)(?:&(?:[-\w~!$+|.,*:]|%[a-f\d{2}])+=?(?:[-\w~!$+|.,*:=]|%[a-f\d]{2})*)*)*(?:#(?:[-\w~!$+|.,*:=]|%[a-f\d]{2})*)?$/;
should be the uber-url parsing regex :-) Taken from here http://flanders.co.nz/2009/11/08/a-good-url-regular-expression-repost/
Test here: http://jsfiddle.net/Qznzx/1/
It shows the uselessness of regexes.

This might be a bit more complex than necessary but it seems to work:
^((?:.+?:\/\/)?(?:.[^/:]+)+)$
A non-capturing group for the protocol. From the start of the string
match any number of characters until a :. There may be zero or one
protocol.
A non-capturing group for the rest of the url. This part must exist.
Group it all up in single group.

Breaking a String into Chunks based on Pattern

I have one string, that looks like this:
a[abcdefghi,2,3,jklmnopqr]
The beginning "a" is fixed and non-changing, however the content within the brackets is and can follow a pattern. It will always be an alphabetical string, possibly followed by numbers separate by commas or more strings and/or numbers.
I'd like to be able to break it into chunks of the string and any numbers that follow it until the "]" or another string is met.
Probably best explained through examples and expected ideal results:
a[abcdefghi] -> "abcdefghi"
a[abcdefghi,2] -> "abcdefghi,2"
a[abcdefghi,2,3,jklmnopqr] -> "abcdefghi,2,3" and "jklmnopqr"
a[abcdefghi,2,3,jklmnopqr,stuvwxyz] -> "abcdefghi,2,3" and "jklmnopqr" and "stuvwxyz"
a[abcdefghi,2,3,jklmnopqr,1,9,stuvwxyz] -> "abcdefghi,2,3" and "jklmnopqr,1,9" and "stuvwxyz"
a[abcdefghi,1,jklmnopqr,2,stuvwxyz,3,4] -> "abcdefghi,1" and "jklmnopqr,2" and "stuvwxyz,3,4"
Ideally a malformed string would be partially caught (but this is a nice extra):
a[2,3,jklmnopqr,1,9,stuvwxyz] -> "jklmnopqr,1,9" and "stuvwxyz"
I'm using Javascript and I realize a regex won't bring me all the way to the solution I'd like but it could be a big help. The alternative is to do a lot of manually string parsing which I can do but doesn't seem like the best answer.
Advice, tips appreciated.
UPDATE: Yes I did mean alphametcial (A-Za-z) instead of alphanumeric. Edited to reflect that. Thanks for letting me know.

You'd probably want to do this in 2 steps. First, match against:
a\[([^[\]]*)\]
and extract group 1. That'll be the stuff in the square brackets.
Next, repeatedly match against:
[a-z]+(,[0-9]+)*
That'll match things like "abcdefghi,2,3". After the first match you'll need to see if the next character is a comma and if so skip over it. (BTW: if you really meant alphanumeric rather than alphabetic like your examples, use [a-z0-9]*[a-z][a-z0-9]* instead of [a-z]+.)
Alternatively, split the string on commas and reassemble into your word with number groups.

Why wouldn't a regex bring you all the way to a solution?
The following regex works against the given data, but it makes a few assumptions (at least two alphas followed by comma separated single digits).
([a-z]{2,}(?:,\\d)*)
Example:
re = new RegExp('[a-z]{2,}(?:,\\d)*', 'g')
matches = re.exec("a[abcdefghi,2,3,jklmnopqr,1,9,stuvwxyz]")

Assuming you can easily break out the string between the brackets, something like this might be what you're after:
> re = new RegExp('[a-z]+(?:,\\d)*(?:,?)', 'gi')
> while (match = re.exec("abcdefghi,2,3,jklmnopqr,1,9,stuvwxyz")) { print(match[0]) }
abcdefghi,2,3,
jklmnopqr,1,9,
stuvwxyz
This has the advantage of working partially in your malformed case:
> while (match = re.exec("abcdefghi,2,3,jklmnopqr,1,9,stuvwxyz")) { print(match[0]) }
jklmnopqr,1,9,
stuvwxy
The first character class [a-z] can be modified if you meant for it to be truly alphanumeric.