In the future please do reformat your data when posting. It is not helpful. If someone wanted to run a test against your sample they would have to edit it. Post the actual text as requested in the posting guidelines.

As to your pattern I don't think it matches anything. VBScript may be returning empty strings to whatever you are calling. The \w alone would have to match one character so you should not be able return an empty sting as a match. You can't use the lookahead the way you are trying to at the begining of your pattern.  Lookahead do not consume any characters.  You are trying to examine a character behind the one you want. There is a regex construct for doing this but it is not supported by VBScript. Your lookahead at the end of your pattern is the proper use.

You could just use the regex that was working for you and get the value you want out of the SubMatches.  http://regexadvice.com/blogs/mash/archive/2007/06/01/You_2700_ve-got-your-sub_2D00_matches-in-my-matches.aspx

This is where I would recommend you start:

http://www.regular-expressions.info/

It has sections on the various regex constructs as well as a section on what vbscript does and does not support.

Hey,

I have very basic problem. I want a Regex to validate a fieldvalue which should either be of 11 digits or 15 digits.

 I am using "\d{11}|\d{15}" as pattern but the problem is it gives values as "VALID" if they contain 11 or > 11 digits, gives invalid only in case where digits are less than 11.

Please help...

gur, please start a new message thread if your post is not in response to the original thread.

but, here's a pattern for you to test:

"^(\d{11}|\d{15})$"

In the future start your own post.  Don't hijack someone else's. 

Just reverse the order of your test, and add boundards. What you have simple say finds x number of consecutive digits somewhere in a string.