Regex matching recurring patterns

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?

@SeToY.. Do you want those characters to be same? Like is this allowed - ABCDS-ASDFS-23423...? — Rohit Jain
– Rohit Jain, Commented Dec 22, 2012 at 16:01
@SeToY.. Then your question is not clear about that. Please modify it. — Rohit Jain
– Rohit Jain, Commented Dec 22, 2012 at 16:03
@RohitJain I wasn't mistaken at that point. There's nothing to indicate they should be same, nor is it the usual use-case. — John Dvorak
– John Dvorak, Commented Dec 22, 2012 at 16:04

Rohit Jain · Accepted Answer · 2012-12-22 17:03:19Z

3

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.

edited Dec 22, 2012 at 17:03

answered Dec 22, 2012 at 15:56

Rohit Jain

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5 Comments

John Dvorak Over a year ago

Note the explanation is no longer relevant.

Firas Dib Over a year ago

You can use regex101.com to generate accurate explanations for your regular expressions instead :)

Rohit Jain Over a year ago

@Lindrian. Isn't mine accurate?? Anyways thanks for the link.

Firas Dib Over a year ago

@RohitJain: Sorry if I made it sound that way, it absolutely is. I just meant you could save yourself some time using that website. You can insert an expression and the text you want to match and it breaks it all down for you very nicely. Have a look here: regex101.com/r/iT7sN4 (Happy holidays and have an upvote for a good answer :))

Rohit Jain Over a year ago

@Lindrian.. Ah! No worry. No offense taken really. I knew you didn't meant that. Cheers :)

Michael · Accepted Answer · 2012-12-22 15:55:49Z

1

Untested, but I think this will work:

([A-Za-z0-9]{5}-){6}[A-Za-z0-9]

answered Dec 22, 2012 at 15:55

Michael

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3 Comments

SeToY Over a year ago

This results in having five dashes 1-----2-----3-----4-----5-----6-----

Rohit Jain Over a year ago

@JanDvorak. I inferred that from the posted example in the OP. Anyways, I have asked for clarification.

John Dvorak Over a year ago

@RohitJain As per the clarification, your inference was hasty and incorrect.

Chris Seymour · Accepted Answer · 2012-12-22 15:56:30Z

1

For your example, in general replace C to the character class you want:

^(C{5}-){6}C$

^([a-z]{5}-){6}[a-z]$        # Just letter, use case insensitive modifier 

^([a-z0-9]{5}-){6}[a-z0-9]$  # Letters and digits..

answered Dec 22, 2012 at 15:56

Chris Seymour

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Comments

Olivier Jacot-Descombes · Accepted Answer · 2012-12-22 15:59:54Z

0

Try this:

^(C{5}-){6}C$

The ^ and $ denote the begiining and end of the string repectively and make sure that no additional characters are entered.

answered Dec 22, 2012 at 15:59

Olivier Jacot-Descombes

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