Specific regex in C# .NET

Question

I need to build a regular expression which should apply for the following:

(Valid for 1 - 4 Blocks (seperated with "/") which contain exactly 4 characters that are HEX numbers)

Valid example 1: 3F00 / FA41 / FA12 / B12F
Valid example 2: 4F0T
Valid example 3: FFFF / FF21

Invalid example 1: 34BF /
Invalid example 2: 45FB2
Invalid example 3: 4B5S / BD45 BA56
Invalid example 4: FF02/B200
...

I just can't figure it out. Here's what I have for now:

1: ([0-9A-F]{4})( \/ \1){1,3}|[0-9A-F]{4}
2: [0-9A-F]{4} \/ [0-9A-F]{4} \/ [0-9A-F]{4} \/ [0-9A-F]{4}|[0-9A-F]{4} \/ [0-9A-F]{4} \/ [0-9A-F]{4}|[0-9A-F]{4} \/ [0-9A-F]{4}|[0-9A-F]{4}

Second pretty ugly and both not working!

Do you only want to validate if a line obeys the regex pattern, or do you also want to extract the matched 4-character words? — Good Night Nerd Pride
– Good Night Nerd Pride, Commented Aug 17, 2017 at 13:56

Dmitrii Bychenko · Accepted Answer · 2017-08-17 14:01:09Z

4

I suggest

 ^[0-9A-F]{4}( \/ [0-9A-F]{4}){0,3}$

pattern:

 ^                      - string start
 [0-9A-F]{4}            - 4 hex digits
 ( \/ [0-9A-F]{4}){0,3} - up to 3 more 4 digits groups
 $                      - string end

edited Aug 17, 2017 at 14:01

answered Aug 17, 2017 at 13:58

Dmitrii Bychenko

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2 Comments

Mr. Toast Over a year ago

This allows more than 4 blocks, which would be invalid

Dmitrii Bychenko Over a year ago

@Mr. Toast: if we want up to 4 blocks; {,3} should be used instead of *

Andrew · Accepted Answer · 2017-08-17 14:03:43Z

3

This should do the trick:

^[\dA-F]{4}( \/ [\dA-F]{4}){0,3}$

It matches the first block (4 hex characters) and then optionally matches 0-3 subsequent blocks separated by /.

edited Aug 17, 2017 at 14:03

answered Aug 17, 2017 at 13:58

Andrew

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Comments

Mithrandir · Accepted Answer · 2017-08-17 14:08:19Z

1

I think this might work, if the input is given line by line:

^([0-9A-F]{4})( \/ [0-9A-F]{4}){0,3}$

edited Aug 17, 2017 at 14:08

answered Aug 17, 2017 at 13:47

Mithrandir

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2 Comments

Mr. Toast Over a year ago

Does not work if the blocks contain different characters: FFFF / FFFF = valid; 2222 / 1111 = invalid

Mithrandir Over a year ago

Remove the back reference, then it should work. Sorry forgot to remove that.

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