c# Conditional Regular Expression String Match

Question

I am trying to use c# Regular Expression to match a particular string of characters but I can not figure out how to do it. Any help is appreciated.

The string that I am trying to match is as follows, where A is an uppercase alpha character, X is an upper case alpha-numeric character and # is 0, 1 or 2.

AA-#-XX-X-XXX-XXXXXXX-XXXXXXXX

So any of the following would match the string above.

XY-1

MM-0-AB

MM-0-AB-1-ABC-1234567

VV-2-XX-7-CCC-ABCDEFG-12345678

Any any of the following would NOT match.

QQ-7-AA (Only 0, 1, 2 are allowed at the second level.)

QQ-2-XX-7-CC (Partial characters for that level.)

QQ-2-XX-7-CCC-ABCDEFG- (Can not end in a dash.)

QQ-2-XX-7-CCC-ABCDEFG-123456 (Partial characters for that level.)

So far (not that far really) I have as the pattern to match @"^[A-Z]{2}", but I am unsure how to match conditionally (I'm not even sure if conditionally is the proper term to use) the rest of the string, but only if it is there. Do I need to write 7 different statements for this? Seems unreasonable, but I could be wrong.

dtb · Accepted Answer · 2012-05-21 21:53:22Z

9

Have a look at the Regular Expression Language. You need the following elements:

uppercase alpha character: [A-Z]
upper case alpha-numeric character: [A-Z0-9]
0, 1 or 2: [0-2]
dash: -
match x exactly n times: x{n}
match x zero or one time: x?
define a subexpression: (...)

Examples:

two uppercase alpha characters: [A-Z]{2}
two uppercase alpha characters, followed by a dash: [A-Z]{2}-
two uppercase alpha characters, followed by a dash, followed by 0, 1 or 2: [A-Z]{2}-[0-2]
two uppercase alpha characters, followed by a dash, followed by 0, 1 or 2, but with the subexpression consisting of the dash and 0, 1 or 2 occurring zero or one time:
[A-Z]{2}(-[0-2])?
and so on...

Resulting expression:

^[A-Z]{2}(-[0-2](-[A-Z0-9]{2}(-[A-Z0-9](-[A-Z0-9]{3}(-[A-Z0-9]{7}(-[A-Z0-9]{8})?)?)?)?)?)?$

edited May 21, 2012 at 21:53

answered May 21, 2012 at 21:47

dtb

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3 Comments

Jeroen de Kort Over a year ago

I was so close myself, but you beat me to it. Good and well explained answer! +1

That Chuck Guy Over a year ago

I too was too slow. I thought there was a way to shorten the A-Z0-9 (like using "\d" for the 0-9), but I can't find it. Closest I got was "\w", but that includes too many characters.

JoeFletch Over a year ago

Thanks for the very thorough answer! I now understand the nesting of Regular Expressions!

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