Regular Expression Exercise S1

The first in a series of exercises designed to teach you more about regular expressions, written by a guy who got partway through writing a regex book.

But first, a word about tools. It's a lot easier to use a tool to do this sort of thing than it is to write code to do it. So, I suggest one of the following:

• The Regulator. No fair to use the library if you choose this tool. Uses a bit of code I wrote to analyze regex for you.
• Regular Expression Workbench (classic) . I wrote this
• Regular Expression Workbench (updated). Version with a different UI on it.

So, S stands for simple, 1 stands for 1, so this first one is going to be pretty simple.

S1 - Match a Social Security Number

Verify that a string is a social security number of the format ddd-dd-dddd.

 

Answer and explanation to follow.

Comments

• Anonymous
  October 21, 2005
  ^d{3}-d{2}-d{4}$

• Anonymous
  October 21, 2005
  Surely you'd want the hypens to be optional or replaceable by spaces. Forcing a particlular format when enter a number like this, or a credit-card number can be a pain, unless you explictly tell the user in advance the format you want (as you have done).
  
  In any case, I'd use
  ^d{3}[-| ]?d{2}[-| ]?d{4}$

• Anonymous
  October 23, 2005
  The best tool one can have when working with regular expressions is Regex Coach. http://weitz.de/regex-coach/

• Anonymous
  October 24, 2005
  Dvae:
  Yes, but you'd want consistency in the separator use, so that it would accept "123-12-1234", "123 12 1234" or "123121234" but not "12312 1234" or "123-12 1234". Hence we'd need:
  
  ^d{3}(?<Sep>[- ]?)d{2}<Sep>d{4}$
  
  
  (as interpreted by Regex Workbench)
  
  ^ (anchor to start of string)
  Any digit
  Exactly 3 times
  Capture to <Sep>
  Any character in "- "
  ? (zero or one time)
  End Capture
  Any digit
  Exactly 2 times
  <Sep>
  Any digit
  Exactly 4 times
  $ (anchor to end of string)
  
  

• Anonymous
  October 24, 2005
  > Yes, but you'd want consistency in the separator use
  
  True, but if we wanted consistency, then we'd force them to use the properly structured format, and not allow for any variance ;-)
  
  <strike>Dvae</strike> Dave

• Anonymous
  October 27, 2005
  Why would I want to match one of those? Completely useless outside the US.

• Anonymous
  October 28, 2005
  The comment has been removed

• Anonymous
  November 06, 2005
  The comment has been removed

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