Regex Love

Carole asked me for a quick way to validate some barcode formats for a client. When the barcode is scanned on the device it may only accept a format which looks like this:

1 to 5 digits + "”.” + 6 digits

In other words, at least one but no more than 5 digits followed by a “.” followed by 6 digits.

The regular expression to validate this is:

\b\d{1,5}\.\d{6}$

This breaks down like this:

\b denotes the beginning of a word

d{1,5} means at least one but no more than 5 digits

$ means end of string.

Although I studied Computer Science at university it was many moons ago and I kinda always bunked the regex party. Regular expressions just seemed too hard and it was only when I read this 30 minute tutorial a few years ago that I realized how easy and powerful regular expression were, for some reason suddenly I could grok the whole regex deal. (age?)

They are super efficient (read fast) and if you ever need to pattern match or extract data look no further.

There is a cool utility called RegexBuddy which makes the whole process even easier. Not so much for RegexBuddy’s expression breakdown’s but more for the test environment.

Here’s the C# code:

   1: // array of test strings

   2: string[] aryValues = { "1.123456", "12.123456", "123.123456", "1234.123456", "12345.123456", 

   3:                                              "123456.12345667", "1234567.12345667", "12345678.123456678" };

   4:  

   5: foreach (string s in aryValues)

   6: {

   7:  

   8:     if (Regex.IsMatch(s,@"\b\d{1,5}\.\d{6}$"))

   9:     

  10:         System.Diagnostics.Debug.WriteLine(string.Format("{0} is valid.", s));

  11:  

  12:     else

  13:  

  14:         System.Diagnostics.Debug.WriteLine(string.Format("{0} is NOT valid.", s));

  15:     

  16: }

And the results…

1.123456 is valid.

12.123456 is valid.

123.123456 is valid.

1234.123456 is valid.

12345.123456 is valid.

123456.12345667 is NOT valid.

1234567.12345667 is NOT valid.

12345678.123456678 is NOT valid.