Can I shorten this regular expression?

Question

I have the need to check whether strings adhere to a particular ID format.

The format of the ID is as follows:

aBcDe-fghIj-KLmno-pQRsT-uVWxy

A sequence of five blocks of five letters upper case or lower case, separated by one dash.

I have the following regular expression that works:

string idFormat = "[a-zA-Z]{5}[-]{1}[a-zA-Z]{5}[-]{1}[a-zA-Z]{5}[-]{1}[a-zA-Z]{5}[-]{1}[a-zA-Z]{5}";

Note that there is no trailing dash, but the all of the blocks within the ID follow the same format. Therefore, I would like to be able to represent this sequence of four blocks with a trailing dash inside the regular expression and avoid the duplication.

I tried the following, but it doesn't work:

string idFormat = "[[a-zA-Z]{5}[-]{1}]{4}[a-zA-Z]{5}";

How do I shorten this regular expression and get rid of the duplicated parts?

What is the best way to ensure that each block does also not contain any numbers?

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Edit:

Thanks for the replies, I now understand the grouping in regular expressions.

I'm running a few tests against the regular expression, the following are relevant:

Test 1: aBcDe-fghIj-KLmno-pQRsT-uVWxy
Test 2: abcde-fghij-klmno-pqrst-uvwxy

With the following regular expression, both tests pass:

^([a-zA-Z]{5}-){4}[a-zA-Z]{5}$

With the next regular expression, test 1 fails:

^([a-z]{5}-){4}[a-z]{5}$

Several answers have said that it is OK to omit the A-Z when using a-z, but in this case it doesn't seem to be working.

Answer 1

You can try:

([a-z]{5}-){4}[a-z]{5}

and make it case insensitive.