Re: Are single character sub-domains allowed in the envelope?

[John Peacock]

Michael Holzt wrote:
I'm still trying to decode that regexp (will have a look in the camel book
later)
Does this help?
$ perl -Mre=debug -e "qr'(?:[a-zA-Z0-9](?:[-a-zA-Z0-9]*[a-zA-Z0-9])?)';" 
       Freeing REx: `","'
Compiling REx `(?:[a-zA-Z0-9](?:[-a-zA-Z0-9]*[a-zA-Z0-9])?)'
size 39 Got 316 bytes for offset annotations.
first at 1
   1: ANYOF[0-9A-Za-z](12)
  12: CURLYX[0] {0,1}(38)
  14:   STAR(26)
  15:     ANYOF[\-0-9A-Za-z](0)
  26:   ANYOF[0-9A-Za-z](37)
  37:   WHILEM(0)
  38: NOTHING(39)
  39: END(0)
stclass `ANYOF[0-9A-Za-z]' minlen 1

How about this ?
my $subdomain = qr'
    (?:                    # group but no backreferences
      [a-zA-Z0-9]          # match a single ALPHA / DIGIT
        (?:                # group but no backreferences
            [-a-zA-Z0-9]*  # match zero or more ALPHA / DIGIT / HYPHEN
            [a-zA-Z0-9]    # followed by a single ALPHA / DIGIT
        )?                 # but only optionally match this group
    )'x;
However, now that I diagram this out, I think this is still too 
limiting.  Here is the BNF notation for the subdomain term:

#   sub-domain = Let-dig [Ldh-str]
#   Let-dig = ALPHA / DIGIT
#   Ldh-str = *( ALPHA / DIGIT / "-" ) Let-dig
so we have to match
        u.domain.edu
        u-u.domain.edu
        university-something.domain.edu
which I don't think that regex manages.  Isn't this better?
my $subdomain = qr'
    (?:                    # group but no backreferences
      [a-zA-Z0-9]          # match a single ALPHA / DIGIT
        (?:                # group but no backreferences
          -(?=[a-zA-Z0-9]) # match HYPHEN when followed by ALPHA / DIGIT
        )?                 # but only optionally match this group
      [a-zA-Z0-9]*         # followed by a zero or more ALPHA / DIGIT
    )'x;
Right???
John