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I need to create a regex that identify a string if that is a url with my criteria but i got stuck in identifying the domain name...

the criteria for domain name is

  1. only [a-z][0-9], . and -
  2. first char must be [a-z]
  3. before and after . or - must be [a-z]
  4. min length 1 char

and the domain region is

  1. only [a-z] and .
  2. first char must be .
  3. min length 3 char

format should be www.<domain name>.<domain region>

here what i got..

www.[a-z]([a-z0-9\.\-]{1,}[a-z][\.\-])+[^\.+\-].[a-z+\.]{2,}[^\.]$

this is for the domain name 

[a-z]([a-z0-9\.\-]{1,}[a-z][\.\-])+[^\.+\-]

this is for the domain region

.[a-z+\.]{2,}[^\.]$

this will be www.sample.com.sg

  • www..sample.com will be rejected because of .sample
  • www.sample..com will be rejected because of sample.
  • www.sample.com.sg. will be rejected because of .com.sg.
  • www.sampl3.sample.com will be rejected because of sampl3. rules numb 3.
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  • here is a start: www\.[a-z]([.-][a-z]|[a-z0-9])+ Commented Sep 24, 2012 at 13:45
  • are you sure about rule 3? What is wrong with all-4-one.com? Commented Sep 24, 2012 at 13:46
  • thx.. 4 ur fast response.. but at the end of domain name, it can't be a '.' or '-'.. how can i validate that? err.. i don't think this is a great criteria for identifying a url, but i got a assignment and this is the criteria my lecturer give.. so thats why..ahahahhaa..xD Commented Sep 24, 2012 at 13:48
  • it is only a start. It should take you up to the TLD - but not with your extra rule about only letters around hyphens. Commented Sep 24, 2012 at 14:16
  • hahaha.. yes.. that's true.. with this extra rules this can't be TLD..@_@ Commented Sep 24, 2012 at 14:21

3 Answers 3

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Reinvent not

Things like this have been done so many times, it's better to leverage the existing code than to relearn all the URL rules and spec requirements.

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yes.. that's will be a great way to identify the url in easier way..but i have to go with the regex.. so thx for answering..:D
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Try this one out: ^[a-zA-Z0-9-.]+.(com|org|net|mil|edu|COM|ORG|NET|MIL|EDU)$ I haven't pretested it, so few regulations may be necessary

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3 Comments

hmm.. i've seen that code before.. but i have to go with that criteria i described above..anyway thanks for answering..:D
com/org etc fails to match anything outside the US; .eu, .co.uk, .it. It will even fail with common things like .me, bit.ly etc.
yes.. and that's only for the domain name that u mentioned (com|org|net|mil|edu|COM|ORG|NET|MIL|EDU).. other than that will fail
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EDIT:

www\.(([a-z][a-z0-9]*)?[a-z][\.\-])*([a-z][a-z0-9]*)?[a-z]\.[a-z]{2,}$

Crazy long so maybe there's better ones but...

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6 Comments

Yeah i missed the that the domain name must start with [a-z] but was it more than that? I'll edit the regExp.
Missed the [a-z] before and after [\.\-] part to
ahahha... yes.. and the last of domain name cannot be a . or -.. and there cant be numbers before . and -..@_@
what if it's like this [a-z]([a-z]+[0-9]*[a-z]+|[\.\-])+
i dont really get what ? means??.. @@
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