Question

I want to validate input in a C# TextBox by using regular expressions. The expected input is in this format:
CCCCC-CCCCC-CCCCC-CCCCC-CCCCC-CCCCC-C

So I’ve got six elements of five separated characters and one separated character at the end.

Now my regex matches any character between five and 255 chars: .{5,255}

How do I need to modify it in order to match the format mentioned above?

Answer 1

Update: –

If you want to match any character, then you can use: –

^(?:[a-zA-Z0-9]{5}-){6}[a-zA-Z0-9]$

Explanation: –

(?:                // Non-capturing group
    [a-zA-Z0-9]{5} // Match any character or digit of length 5
    -              // Followed by a `-`
){6}               // Match the pattern 6 times (ABCD4-) -> 6 times
[a-zA-Z0-9]        // At the end match any character or digit.

---

Note: – The below regex will only match pattern like you posted: –

CCCCC-CCCCC-CCCCC-CCCCC-CCCCC-CCCCC-C

You can try this regex: –

^(?:([a-zA-Z0-9])\1{4}-){6}\1$

Explanation: –

(?:                // Non-capturing group
  (                // First capture group
    [a-zA-Z0-9]    // Match any character or digit, and capture in group 1
  )
  \1{4}            // Match the same character as in group 1 - 4 times
  -                // Followed by a `-`
){6}               // Match the pattern 6 times (CCCCC-) -> 6 times
\1                 // At the end match a single character.