Regex to match a 2-digit number (to validate Credit/Debit Card Issue number)

Question

I would like to use regex to match a string of exactly 2 characters, and both of those characters have to be between 0 and 9. The string to match against would be coming from a single-line text input field when an ASP.NET MVC view is rendered

So far, I have the regex

[0-9]{2} 

and from the following list of example string inputs

• 456
• 55 44
• 12

the following matches are returned when I apply the regex

• 45
• 55
  44
• 12

So, I have kind of half the solution....what I actually want to enforce is that the string is also exactly 2 characters long, so that from the list of strings, the only one that should be matched is

12 

I am an admitted amateur at regular expressions and am just using this to validate a card issue number on an ASP.NET MVC model as below....

[Required] [RegularExpression("[0-9]{2}")] public string IssueNumber { get; set; } 

I'm sure that what i'm asking is quite simple but I wasn't able to find any examples that limited the length as part of the matching .

Thanks, in advance.

Answer 1

You can use the start (^) and end ($) of line indicators:

^[0-9]{2}$ 

Some language also have functions that allows you to match against an entire string, where-as you were using a find function. Matching against the entire string will make your regex work as an alternative to the above. The above regex will also work, but the ^ and $ will be redundant.