From: Vincent Fourmond <vincent.fourmond@9online.fr>
Date: 2007-01-10T23:47:32+09:00
Subject: Re: Is [:alnum:] equivalent to [A-Za-z0-9]?

Jeff wrote:
> Hi,
> 
> I'm trying to creating a regex that will match a string that starts and
> ends with an alphanumeric character, and has alphanumeric characters or
> dashes in the middle.
> 
> This regex gives the expected result:
> irb(main):008:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple!"
> => nil
> irb(main):009:0> /^[:alnum:][A-Za-z0-9\-]*[A-Za-z0-9]$/ =~ "apple"
> => 0
> 
> This regex works as expected on "apple!", but returns nil on "apple":
> irb(main):010:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple!"
> => nil
> irb(main):011:0> /^[:alnum:][A-Za-z0-9\-]*[:alnum:]$/ =~ "apple"
> => nil
> 
> Can anyone explain this?

  Yes, that's a classical mistake: POSIX specifications of this kind
must be included inside other []. Try rather

/^[[:alnum:]][A-Za-z0-9\-]*[[:alnum:]]$/

  The way you wrote it just meant ':' or 'a' or 'l' or...

	Vince

-- 
Vincent Fourmond, PhD student
http://vincent.fourmond.neuf.fr/