subdomain extract without regex with php

Question

is there a great way to extract subdomain with php without regex ?

why without regex ?

there are a lot of topic about this, one if them is Find out subdomain using Regular Expression in PHP

the internet says it consumes memory a lot, if there is any consideration or you think better use regex ( maybe we use a lot of function to get this solution ) please comment below too.

example

static.x.com = 'static'
helloworld.x.com = 'helloworld'
b.static.ak.x.com = 'b.static.ak'
x.com = ''
www.x.com = ''

Thanks for looking in.

Adam Ramadhan

A regex in a case like this is trivial and by no means does it consume "memory a lot" — Matteo Riva
– Matteo Riva, Commented Mar 17, 2011 at 13:55
Is this really a safe/wise data collection method? for instance: www.bbc.co.uk — horatio
– horatio, Commented Mar 17, 2011 at 14:31
horatio umm yes, thats why, im asking this. i my self use a .co.id :| — Adam Ramadhan
– Adam Ramadhan, Commented Mar 17, 2011 at 16:30

Grad van Horck · Accepted Answer · 2011-03-17 13:53:35Z

3

http://php.net/explode ?

Just split them on the dot? And do some functions?

Or if the last part (x.com) is the same everytime, do a substring on the hostname, stripping of the last part.

The only exception you'll have to make in your handling is the www.x.com (which technically is a subdomain).

$hostname = '....';
$baseHost = 'x.com';

$subdomain = substr($hostname, 0, -strlen($baseHost));
if ($subdomain === 'www') {
  $subdomain = '';
}

answered Mar 17, 2011 at 13:53

Grad van Horck

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Comments

ThiefMaster · Accepted Answer · 2011-03-17 13:53:20Z

1

Whoever told you that regexes "consume a lot" was an idiot. Simple regexes are not very cpu/memory-consuming.

However, for your purpose a regex is clearly overkill. You can explode() the string and then take as many elements from the array as you need. However, your last example is really bad. www is a perfectly valid subdomain.

answered Mar 17, 2011 at 13:53

ThiefMaster

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3 Comments

NikiC Over a year ago

+1 for calling that guy an idiot. A stupid and ignorant idiot.

Adam Ramadhan Over a year ago

wew thank you. everyone says that, or maybe there are a lot of cargo cult programmer in the world of www.

Marc B Over a year ago

regexes CAN potentially use a lot of memory, but it depends on the pattern. To say they 'always' consume is definitely wrong. But it's also wrong to say they don't ever.

Jakob Alexander Eichler · Accepted Answer · 2011-03-17 13:54:07Z

1

You can first use parse_url http://www.php.net/manual/de/function.parse-url.php and than explode with . as delimiter on the host http://www.php.net/manual/de/function.explode.php

I would not say it is quicker (just test it), but maybe this solution is better.

answered Mar 17, 2011 at 13:54

Jakob Alexander Eichler

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Comments

NikiC · Accepted Answer · 2011-03-17 14:03:44Z

0

function getSubdomain($host) {
    return implode('.', explode('.', $host, -2));
}

explode splits the string on the dot and drops the last two elements. Then implode combines these pieces again using the dot as separator.

edited Mar 17, 2011 at 14:03

answered Mar 17, 2011 at 13:58

NikiC

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1 Comment

NikiC Over a year ago

@Adam: www.bbc is the subdomain in this case. Technically speaking, this is correct.

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