Regex to match string 2 times but not 3

Question

I try to regex match string like these examples:

NetTAP IPX C-4-16

SmartTAP DP6409 Dual E1-11-16

but not these ones:

NetTAP IPX C-4-16-0

SmartTAP DP6409 Dual E1-11-16-0

SYSTEM

I've tried some solutions without success.

My idea was to search the -\d\d 2 times but not 3 times

(?!\-\d+)(\-\d+){2}$

or

[^(\-\d+)](\-\d+){2}$

Could you help me?

Answer 1

You can use

(?<!-\d+)(?:-\d+){2}$

See the regex demo . Details :

• (?<!-\d+) - a negative lookbehind that fails the match if there is a - char and one or more digits immediately to the left of the current location
• (?:-\d+){2} - two repetitions of - and one or more digits
• $ - end of string.

Answer 2

You can also match 3 times what you want to avoid, and capture 2 times what you want to keep using a capture group.

(?:-\d+){3}$|(-\d+-\d+)$

The pattern matches:

• (?:-\d+){3}$ Match 3 repetitions at the end of the string
• | Or
• (-\d+-\d+)$ capture 2 repetitions at the end of the string in group 1

Regex demo