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4GuysFromRolla.com : ASP FAQS : Regular Expressions


How can I use regular expressions to help validate that a user-entered value is in a proper format?

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Answer: Regular expressions are very handy for patern matching. So, if you are letting your users enter information into a form that must conform to a specific format (such as zip codes, social security numbers, phone numbers, etc.), regular expressions can provide a very easy way to ensure that a user's entry is in the proper format.

You can create a generic function that will except two parameters: a string to check and the valid regular expression. This function will return True if the string to check is valid according to the passed-in regular expression; it will return False otherwise. Below you can see this simple function:

Function CheckString(strToCheck, strRegExp)
  Dim re
  Set re = new RegExp

  re.IgnoreCase = false
  re.global = false
  re.Pattern = strRegExp

  CheckString = re.Test(strToCheck)
End Function

You can then read in a user's form field entry into a string and call this function to ensure that it is the valid format. For example, if on our form we have a text box named txtSSN that is for the user to enter her social security number, we can check to see if the user's social security is in a valid format using this function like so:

'... Assumes the CheckString function has been defined above ...

'Read in the user-entered social security number
Dim strSSN
strSSN = Request("txtSSN")

'Make sure it's in the format XXX-XX-XXXX (where each X is a digit)
If CheckString(strSSN, "^\d{3}\-\d{2}\-\d{4}$") then
  'strSSN is valid!
  'strSSN is NOT valid
End If

Pretty simple, eh? Here are some common regular expressions for checking various field types:

Phone number - valid format: (XXX) XXX-XXXX
^\(\d{3}\) \d{3}\-\d{4}$

Zip code - valid format: XXXXX or XXXXX-XXXX

For more information on regular expressions be sure to check out the Regular Expressions Article Index. Happy Programming!

FAQ posted by Scott Mitchell at 2/17/2001 11:37:03 PM to the Regular Expressions category. This FAQ has been viewed 55,747 times.

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Last computed at 9/17/2007 3:22:00 AM

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