Regex validation: valid matches not found

Question

Hi
I'm trying to use a regex to validate the format (not the content!) of email addresses. The best regex if found for this so far is
^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$which I've tested using http://regexlib.com/RETester.aspx
Strings which produce matches using this tester fail validation when I use the same pattern as an item-level validation on an Apex page.
I know that there are some different regex dialects out there, so maybe that's the problem...
Can anybody help out with an explanation - or even a fix :) ?
Many thanks
john

Answer 1

The problem seems to be a missing "*" metacharacter. I've put a small test case together:
WITH t AS (SELECT '[email protected]' email
             FROM dual
            UNION
           SELECT '[email protected]'
             FROM dual
SELECT t.email
     , REGEXP_SUBSTR(t.email, '^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$') orig_check
     , REGEXP_SUBSTR(t.email, '^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z]*[-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$') new_check
  FROM t
  ;        I'm going to deal with inet specific values (IP4 addresses, emails, URLs) in the second part of my regex introduction.
C.