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I'm not very good at regular expressions at all.
I've been using a lot of framework code to date, but I'm unable to find one that is able to match a URL like http://www.example.com/etcetc, but it is also is able to catch something like www.example.com/etcetc and example.com/etcetc.
For matching all kinds of URLs, the following code should work:
<?php
$regex = "((https?|ftp)://)?"; // SCHEME
$regex .= "([a-z0-9+!*(),;?&=$_.-]+(:[a-z0-9+!*(),;?&=$_.-]+)?#)?"; // User and Pass
$regex .= "([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))"; // Host or IP address
$regex .= "(:[0-9]{2,5})?"; // Port
$regex .= "(/([a-z0-9+$_%-]\.?)+)*/?"; // Path
$regex .= "(\?[a-z+&\$_.-][a-z0-9;:#&%=+/$_.-]*)?"; // GET Query
$regex .= "(#[a-z_.-][a-z0-9+$%_.-]*)?"; // Anchor
?>
Then, the correct way to check against the regex is as follows:
<?php
if(preg_match("~^$regex$~i", 'www.example.com/etcetc', $m))
var_dump($m);
if(preg_match("~^$regex$~i", 'http://www.example.com/etcetc', $m))
var_dump($m);
?>
Courtesy: Comments made by splattermania in the PHP manual: preg_match
RegEx Demo in regex101
This worked for me in all cases I had tested:
$url_pattern = '/((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]+\.([a-zA-Z0-9\&\.\/\?\:#\-_=#])*/';
Tests:
http://test.test-75.1474.stackoverflow.com/
https://www.stackoverflow.com
https://www.stackoverflow.com/
http://wwww.stackoverflow.com/
http://wwww.stackoverflow.com
http://test.test-75.1474.stackoverflow.com/
http://www.stackoverflow.com
http://www.stackoverflow.com/
stackoverflow.com/
stackoverflow.com
http://www.example.com/etcetc
www.example.com/etcetc
example.com/etcetc
user:pass#example.com/etcetc
example.com/etcetc?query=aasd
example.com/etcetc?query=aasd&dest=asds
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www/
Every valid Internet URL has at least one dot, so the above pattern will simply try to find any at least two strings chained by a dot and has valid characters that URL may have.
Try this:
/^http:\/\/|(www\.)?[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(:[0-9]{1,5})?(\/.*)?$/
It works exactly like the people want.
It takes with or with out http://, https://, and www.
You can use a question mark after a regular expression to make it conditional so you would want to use:
http:\/\/(www\.)?
That will match anything that has either http://www. or http:// (with no www.)
You could just use a replace method to remove the above, thus getting you the domain. It depends on what you need the domain for.
Try something like this:
.*([\w-]+\.)+[a-z]{2,5}(/[\w-]+)*
Use:
/(https?://)?((?:(\w+-)*\w+)\.)+(?:[a-z]{2})(\/?\w?-?=?_?\??&?)+[\.]?([a-z0-9\?=&_\-%#])?/g
It matches something.com, http(s):// or www. It does not match other [something]:// URLs though, but for my purpose that's not necessary.
The regex matches e.g.:
http://foo.co.uk/
www.regex.com/foo.html?q=bar$some=thi-ng,regex
regex.foo.com/blog
You can try this:
r"(http[s]:\/\/)?([\w-]+\.)+([a-z]{2,5})(\/+\w+)? "
Selection:
may be start with http:// or https:// (optional)
anything (word) end with dot (.)
followed by 2 to 5 character [a-z]
followed by "/[anything]" (optional)
followed by space
Try this
$url_reg = /(ftp|https?):\/\/(\w+:?\w*#)?(\S+)(:[0-9]+)?(\/([\w#!:.?+=&%#!\/-])?)?/;
I have been using the following, which works for all my test cases, as well as fixes any issues where it would trigger at the end of a sentence preceded by a full-stop (end.), or where there were single character initials, such as 'C.C. Plumbing'.
The following regex contains multiple {2,}s, which means two or more matches of the previous pattern.
((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]{2,}\.([a-zA-Z0-9\&\.\/\?\:#\-_=#]){2,}
Matches URLs such as, but not limited to:
https://example.com
http://example.com
example.com
example.com/test
example.com?value=test
Does not match non-URLs such as, but not limited to:
C.C Plumber
A full-stop at the end of a sentence.
Single characters such as a.b or x.y
Please note: Due to the above, this will not match any single character URLs, such as: a.co, but it will match if it is preceded by a URL scheme, such as: http://a.co.
I was getting so many issues getting the answer from anubhava to work due to recent PHP allowing $ in strings and the preg match wasn't working.
Here is what I used:
// Regular expression
$re = '/((https?|ftp):\/\/)?([a-z0-9+!*(),;?&=.-]+(:[a-z0-9+!*(),;?&=.-]+)?#)?([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))(:[0-9]{2,5})?(\/([a-z0-9+%-]\.?)+)*\/?(\?[a-z+&$_.-][a-z0-9;:#&%=+\/.-]*)?(#[a-z_.-][a-z0-9+$%_.-]*)?/i';
// Match all
preg_match_all($re, $blob, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
// The first element of the array is the full match
This PHP Composer package URL highlight is doing a good job in PHP:
<?php
use VStelmakh\UrlHighlight\UrlHighlight;
$urlHighlight = new UrlHighlight();
$matches = $urlHighlight->getUrls($string);
?>
If it does not have to be regex, you could always use the validate filters that are in PHP.
filter_var('http://example.com', FILTER_VALIDATE_URL);
filter_var (mixed $variable [, int $filter = FILTER_DEFAULT [, mixed $options ]]);
Types of Filters
Validate Filters
Regex if you want to ensure a URL starts with HTTP/HTTPS:
https?:\/\/(www\.)?[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
If you do not require the HTTP protocol:
[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
I'm not very good at regular expressions at all.
I've been using a lot of framework code to date, but I'm unable to find one that is able to match a URL like http://www.example.com/etcetc, but it is also is able to catch something like www.example.com/etcetc and example.com/etcetc.
For matching all kinds of URLs, the following code should work:
<?php
$regex = "((https?|ftp)://)?"; // SCHEME
$regex .= "([a-z0-9+!*(),;?&=$_.-]+(:[a-z0-9+!*(),;?&=$_.-]+)?#)?"; // User and Pass
$regex .= "([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))"; // Host or IP address
$regex .= "(:[0-9]{2,5})?"; // Port
$regex .= "(/([a-z0-9+$_%-]\.?)+)*/?"; // Path
$regex .= "(\?[a-z+&\$_.-][a-z0-9;:#&%=+/$_.-]*)?"; // GET Query
$regex .= "(#[a-z_.-][a-z0-9+$%_.-]*)?"; // Anchor
?>
Then, the correct way to check against the regex is as follows:
<?php
if(preg_match("~^$regex$~i", 'www.example.com/etcetc', $m))
var_dump($m);
if(preg_match("~^$regex$~i", 'http://www.example.com/etcetc', $m))
var_dump($m);
?>
Courtesy: Comments made by splattermania in the PHP manual: preg_match
RegEx Demo in regex101
This worked for me in all cases I had tested:
$url_pattern = '/((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]+\.([a-zA-Z0-9\&\.\/\?\:#\-_=#])*/';
Tests:
http://test.test-75.1474.stackoverflow.com/
https://www.stackoverflow.com
https://www.stackoverflow.com/
http://wwww.stackoverflow.com/
http://wwww.stackoverflow.com
http://test.test-75.1474.stackoverflow.com/
http://www.stackoverflow.com
http://www.stackoverflow.com/
stackoverflow.com/
stackoverflow.com
http://www.example.com/etcetc
www.example.com/etcetc
example.com/etcetc
user:pass#example.com/etcetc
example.com/etcetc?query=aasd
example.com/etcetc?query=aasd&dest=asds
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www/
Every valid Internet URL has at least one dot, so the above pattern will simply try to find any at least two strings chained by a dot and has valid characters that URL may have.
Try this:
/^http:\/\/|(www\.)?[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(:[0-9]{1,5})?(\/.*)?$/
It works exactly like the people want.
It takes with or with out http://, https://, and www.
You can use a question mark after a regular expression to make it conditional so you would want to use:
http:\/\/(www\.)?
That will match anything that has either http://www. or http:// (with no www.)
You could just use a replace method to remove the above, thus getting you the domain. It depends on what you need the domain for.
Try something like this:
.*([\w-]+\.)+[a-z]{2,5}(/[\w-]+)*
Use:
/(https?://)?((?:(\w+-)*\w+)\.)+(?:[a-z]{2})(\/?\w?-?=?_?\??&?)+[\.]?([a-z0-9\?=&_\-%#])?/g
It matches something.com, http(s):// or www. It does not match other [something]:// URLs though, but for my purpose that's not necessary.
The regex matches e.g.:
http://foo.co.uk/
www.regex.com/foo.html?q=bar$some=thi-ng,regex
regex.foo.com/blog
You can try this:
r"(http[s]:\/\/)?([\w-]+\.)+([a-z]{2,5})(\/+\w+)? "
Selection:
may be start with http:// or https:// (optional)
anything (word) end with dot (.)
followed by 2 to 5 character [a-z]
followed by "/[anything]" (optional)
followed by space
Try this
$url_reg = /(ftp|https?):\/\/(\w+:?\w*#)?(\S+)(:[0-9]+)?(\/([\w#!:.?+=&%#!\/-])?)?/;
I have been using the following, which works for all my test cases, as well as fixes any issues where it would trigger at the end of a sentence preceded by a full-stop (end.), or where there were single character initials, such as 'C.C. Plumbing'.
The following regex contains multiple {2,}s, which means two or more matches of the previous pattern.
((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]{2,}\.([a-zA-Z0-9\&\.\/\?\:#\-_=#]){2,}
Matches URLs such as, but not limited to:
https://example.com
http://example.com
example.com
example.com/test
example.com?value=test
Does not match non-URLs such as, but not limited to:
C.C Plumber
A full-stop at the end of a sentence.
Single characters such as a.b or x.y
Please note: Due to the above, this will not match any single character URLs, such as: a.co, but it will match if it is preceded by a URL scheme, such as: http://a.co.
I was getting so many issues getting the answer from anubhava to work due to recent PHP allowing $ in strings and the preg match wasn't working.
Here is what I used:
// Regular expression
$re = '/((https?|ftp):\/\/)?([a-z0-9+!*(),;?&=.-]+(:[a-z0-9+!*(),;?&=.-]+)?#)?([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))(:[0-9]{2,5})?(\/([a-z0-9+%-]\.?)+)*\/?(\?[a-z+&$_.-][a-z0-9;:#&%=+\/.-]*)?(#[a-z_.-][a-z0-9+$%_.-]*)?/i';
// Match all
preg_match_all($re, $blob, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
// The first element of the array is the full match
This PHP Composer package URL highlight is doing a good job in PHP:
<?php
use VStelmakh\UrlHighlight\UrlHighlight;
$urlHighlight = new UrlHighlight();
$matches = $urlHighlight->getUrls($string);
?>
If it does not have to be regex, you could always use the validate filters that are in PHP.
filter_var('http://example.com', FILTER_VALIDATE_URL);
filter_var (mixed $variable [, int $filter = FILTER_DEFAULT [, mixed $options ]]);
Types of Filters
Validate Filters
Regex if you want to ensure a URL starts with HTTP/HTTPS:
https?:\/\/(www\.)?[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
If you do not require the HTTP protocol:
[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
I am looking for a way to get a valid url out of a string like:
$string = 'http://somesite.com/directory//sites/9/my_forms/3-895a3e/somefilename.jpg|:||:||:||:|19845';
My original solution was:
preg_match('#^[^:|]*#', str_replace('//', '/', $string), $modifiedPath);
But obviously its going to remove a slash from the http:// instead of the one in the middle of the string.
My expected output that I want from the original is:
http://somesite.com/directory/sites/9/my_forms/3-895a3e/somefilename.jpg
I could always break off the http part of the string first but would like a more elegant solution in the form of regex if possible. Thanks.
This will do exactly what you are asking:
<?php
$string = 'http://somesite.com/directory//sites/9/my_forms/3-895a3e/somefilename.jpg|:||:||:||:|19845';
preg_match('/^([^|]+)/', $string, $m); // get everything up to and NOT including the first pipe (|)
$string = $m[1];
$string = preg_replace('/(?<!:)\/\//', '/' ,$string); // replace all occurrences of // as long as they are not preceded by :
echo $string; // outputs: http://somesite.com/directory/sites/9/my_forms/3-895a3e/somefilename.jpg
exit;
?>
EDIT:
(?<!X) in regular expressions is the syntax for what is called a lookbehind. The X is replaced with the character(s) we are testing for.
The following expression would match every instance of double slashes (/):
\/\/
But we need to make sure that the match we are looking for is NOT preceded by the : character so we need to 'lookbehind' our match to see if the : character is there. If it is then we don't want it to be counted as a match:
(?<!:)\/\/
The ! is what says NOT to match in our lookbehind. If we changed it to (?=:)\/\/ then it would only match the double slashes that did have the : preceding them.
Here is a Quick tutorial that can explain it all better than I can lookahead and lookbehind tutorial
Assuming all your strings are in the form given, you don't need any but the simplest of regexes to do this; if you want an elegant solution, then a regex is definitely not what you need. Also, double slashes are legal in a URL, just like in a Unix path, and mean the same thing a single slash does, so you don't really need to get rid of them at all.
Why not just
$url = array_shift(preg_split('/\|/', $string));
?
If you really, really care about getting rid of the double slashes in the URL, then you can follow this with
$url = preg_replace('/([^:])\/\//', '$1/', $url);
or even combine them into
$url = preg_replace('/([^:])\/\//', '$1/', array_shift(preg_split('/\|/', $string)));
although that last form gets a little bit hairy.
Since this is a quite strictly defined situation, I'd consider just one preg to be the most elegant solution.
From the top of my head:
$sanitizedURL = preg_replace('~((?<!:)/(?=/)|\\|.+)~', '', $rawURL);
Basically, what this does is look for any forward slash that IS NOT preceded by a colon (:), and IS followed bij another forward slash. It also searches for any pipe character and any character following it.
Anything found is removed from the result.
I can explain the RegEx in more detail if you like.
I'm not very good at regular expressions at all.
I've been using a lot of framework code to date, but I'm unable to find one that is able to match a URL like http://www.example.com/etcetc, but it is also is able to catch something like www.example.com/etcetc and example.com/etcetc.
For matching all kinds of URLs, the following code should work:
<?php
$regex = "((https?|ftp)://)?"; // SCHEME
$regex .= "([a-z0-9+!*(),;?&=$_.-]+(:[a-z0-9+!*(),;?&=$_.-]+)?#)?"; // User and Pass
$regex .= "([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))"; // Host or IP address
$regex .= "(:[0-9]{2,5})?"; // Port
$regex .= "(/([a-z0-9+$_%-]\.?)+)*/?"; // Path
$regex .= "(\?[a-z+&\$_.-][a-z0-9;:#&%=+/$_.-]*)?"; // GET Query
$regex .= "(#[a-z_.-][a-z0-9+$%_.-]*)?"; // Anchor
?>
Then, the correct way to check against the regex is as follows:
<?php
if(preg_match("~^$regex$~i", 'www.example.com/etcetc', $m))
var_dump($m);
if(preg_match("~^$regex$~i", 'http://www.example.com/etcetc', $m))
var_dump($m);
?>
Courtesy: Comments made by splattermania in the PHP manual: preg_match
RegEx Demo in regex101
This worked for me in all cases I had tested:
$url_pattern = '/((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]+\.([a-zA-Z0-9\&\.\/\?\:#\-_=#])*/';
Tests:
http://test.test-75.1474.stackoverflow.com/
https://www.stackoverflow.com
https://www.stackoverflow.com/
http://wwww.stackoverflow.com/
http://wwww.stackoverflow.com
http://test.test-75.1474.stackoverflow.com/
http://www.stackoverflow.com
http://www.stackoverflow.com/
stackoverflow.com/
stackoverflow.com
http://www.example.com/etcetc
www.example.com/etcetc
example.com/etcetc
user:pass#example.com/etcetc
example.com/etcetc?query=aasd
example.com/etcetc?query=aasd&dest=asds
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www
http://stackoverflow.com/questions/6427530/regular-expression-pattern-to-match-url-with-or-without-http-www/
Every valid Internet URL has at least one dot, so the above pattern will simply try to find any at least two strings chained by a dot and has valid characters that URL may have.
Try this:
/^http:\/\/|(www\.)?[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(:[0-9]{1,5})?(\/.*)?$/
It works exactly like the people want.
It takes with or with out http://, https://, and www.
You can use a question mark after a regular expression to make it conditional so you would want to use:
http:\/\/(www\.)?
That will match anything that has either http://www. or http:// (with no www.)
You could just use a replace method to remove the above, thus getting you the domain. It depends on what you need the domain for.
Try something like this:
.*([\w-]+\.)+[a-z]{2,5}(/[\w-]+)*
Use:
/(https?://)?((?:(\w+-)*\w+)\.)+(?:[a-z]{2})(\/?\w?-?=?_?\??&?)+[\.]?([a-z0-9\?=&_\-%#])?/g
It matches something.com, http(s):// or www. It does not match other [something]:// URLs though, but for my purpose that's not necessary.
The regex matches e.g.:
http://foo.co.uk/
www.regex.com/foo.html?q=bar$some=thi-ng,regex
regex.foo.com/blog
You can try this:
r"(http[s]:\/\/)?([\w-]+\.)+([a-z]{2,5})(\/+\w+)? "
Selection:
may be start with http:// or https:// (optional)
anything (word) end with dot (.)
followed by 2 to 5 character [a-z]
followed by "/[anything]" (optional)
followed by space
Try this
$url_reg = /(ftp|https?):\/\/(\w+:?\w*#)?(\S+)(:[0-9]+)?(\/([\w#!:.?+=&%#!\/-])?)?/;
I have been using the following, which works for all my test cases, as well as fixes any issues where it would trigger at the end of a sentence preceded by a full-stop (end.), or where there were single character initials, such as 'C.C. Plumbing'.
The following regex contains multiple {2,}s, which means two or more matches of the previous pattern.
((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:#\-_=#]{2,}\.([a-zA-Z0-9\&\.\/\?\:#\-_=#]){2,}
Matches URLs such as, but not limited to:
https://example.com
http://example.com
example.com
example.com/test
example.com?value=test
Does not match non-URLs such as, but not limited to:
C.C Plumber
A full-stop at the end of a sentence.
Single characters such as a.b or x.y
Please note: Due to the above, this will not match any single character URLs, such as: a.co, but it will match if it is preceded by a URL scheme, such as: http://a.co.
I was getting so many issues getting the answer from anubhava to work due to recent PHP allowing $ in strings and the preg match wasn't working.
Here is what I used:
// Regular expression
$re = '/((https?|ftp):\/\/)?([a-z0-9+!*(),;?&=.-]+(:[a-z0-9+!*(),;?&=.-]+)?#)?([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))(:[0-9]{2,5})?(\/([a-z0-9+%-]\.?)+)*\/?(\?[a-z+&$_.-][a-z0-9;:#&%=+\/.-]*)?(#[a-z_.-][a-z0-9+$%_.-]*)?/i';
// Match all
preg_match_all($re, $blob, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
// The first element of the array is the full match
This PHP Composer package URL highlight is doing a good job in PHP:
<?php
use VStelmakh\UrlHighlight\UrlHighlight;
$urlHighlight = new UrlHighlight();
$matches = $urlHighlight->getUrls($string);
?>
If it does not have to be regex, you could always use the validate filters that are in PHP.
filter_var('http://example.com', FILTER_VALIDATE_URL);
filter_var (mixed $variable [, int $filter = FILTER_DEFAULT [, mixed $options ]]);
Types of Filters
Validate Filters
Regex if you want to ensure a URL starts with HTTP/HTTPS:
https?:\/\/(www\.)?[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
If you do not require the HTTP protocol:
[-a-zA-Z0-9#:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()#:%_\+.~#?&//=]*)
I have a webapp, where people signup and get a sub domain under this app domain ( xx.app.com ) ... for each subdomain there is a db that is attached to it grammatically and have the same name as the subdomain.
what i need is the right regex that works with the subdomain and off course a db name ( mysql if it matters ), it's supposed to be lowercase & the length between 6 and 20 and the only allowed character is the " - ", also numbers are banned ...
i tried many times but it always go bad, .. some like : /([a-z-]){6,20}/
Thanks in advance :)
There might be a right regex for this, but regex isn't right for this.
Try parse_url
Edit:
I am not sure how you are using it. If you are only processing the subdomain part, the following should work and not match numbers:
^[a-z-]{6,20}$
This ensures that the subdomain has only a to z and - and between 6 and 20 times. The ^ matches the beginning of the string and $ matches the end.
The reason the earlier regex was accepting numbers or anything else too was because the match itself would have been a part of the string. Now with the ^ and $ you are ensuring that it is the entire string.
This would be a safer regex, since a subdomain cannot start with an hyphen:
^[a-z][a-z-]{5,19}$
As for the database name I believe it cannot contain an hyphen since it is the subtraction operator, so your best choice might be to either disallow hypens or replace them with underscores:
$database = str_replace('-', '_', $subdomain);
EDIT: Apparently #nikic is right, you can use hyphens as long as you backtick the database name.
Have you tried escaping the hyphen?
/([a-z\-]){6,20}/
You will need positive lookahead regex for this. Try following code:
<?php
$a = array("xx-yyy.domain.cam", "xx4yyy.domain.cam", "abcde.domain.com", "my-sub-domain.domain.org");
foreach ($a as $v) {
echo "For domain $v: ";
preg_match('/^(?:[-a-z]{6,20})(?=\.)/', $v, $m );
if (count($m) > 0)
echo( "subdomain: " . $m[0] . "\n");
else
echo "subdomain not matched\n";
}
?>
Basically match combination of lower case alphabets and hyphen - character of 6 to 20 character length before appearance of first dot . character.
- hyphen need not be escaped if used at the start in square brackets.
OUTPUT
For domain xx-yyy.domain.cam: subdomain: xx-yyy
For domain xx4yyy.domain.cam: subdomain not matched
For domain abcde.domain.com: subdomain not matched
For domain my-sub-domain.domain.org: subdomain: my-sub-domain