[Mythvn]

A valid subdomain may contain letters, digits and many minus signs inside ( - ) but may not starts or ends with a single minus sign. Eg : a-b, cd--12... are valid subdomains but -ab, cd12- are not. Can anyone tell me how to validate a subdomain with Javascript please? Thanks

[=OTS=G-Man]

Regular expressions.

this is the expression you could use

^[^-][a-zA-Z-]+

this is untested but should work.

HTML Code:

<script language="JavaScript1.2">
function checksubdomain()
{
    var validsub=/^[^-][0-9a-zA-Z-]+/ //regular expression defining a string not starting with -'s but can contain alpha, numbers and -'s
    if (document.myform.myinput.value.search(validsub)==-1) //if match failed
        alert("Subdomains can not start with -'s")
}
</script>

<form name="myform">
<input type="text" name="myinput" size=15>
<input type="button" onClick="checksubdomain()" value="check">

</form>

Hope this helps

[=OTS=G-Man]

opps change that expression to ^[^-][0-9a-zA-Z-]+[^-]$ to block names ending with a - also

[Mythvn]

Wow that's really good. It works perfectly. Thank you very much for your help

[Mythvn]

Oops, your regex forgets domains that are shorter than 3 characters, eg : a, cd, e0.... Can you change it please?

[Nico]

^- matches anything except dashes, which includes other characters than aren't allowed in domain names.

Code:

/^[0-9a-z][0-9a-z-]{1,18}[0-9a-z]$/i

... min length 3, max length 20.

Make sure to verify this on the server side as well. Otherwise it'll only be slighlty more secure. You can use the same regex pattern as above in preg_match().

[Mythvn]

I just want to validate on the client side first to reduce http request to the server. Anyway, thanks so much for your help.

[Nico]

Well you should do both.

Most people have Javascript enabled, and this script would prevent extra HTTP requests for most. But not validating on the client side will allow your users to mess up your site.