Isolating groups in regex match

Question

I have am writing a regular expression to return the version number of OpenSSH installed on a Windows machine, for our monitoring system. I have one of two strings:

version=OpenSSH_for_Windows_7.7p1, LibreSSL 2.6.4
version=OpenSSH_7.1p1 Microsoft_Win32_port_with_VS Dec 22 2015, OpenSSL 1.0.2d 9 Jul 2015

When the regex is:

\S+Windows_(\d.\d)

Then 7.7 is in group 1 and the monitoring system sees it. But when I try to cover the 7.1 string, the grouping gets messed up.

(\S+Windows_(\d.\d)|\S+OpenSSH_(\d.\d))

How can I modify that string to isolate group 3 and group 1 (for 7.1 and 7.7 respectively)?

Thanks.

Answer 1

You might consider changing the regex entirely so you only have one capture group.

Both digits you are trying to capture start with version=OpenSSH_ with some optional characters in the middle.

Therefore you can do:

version=OpenSSH_\D*(\d\.\d)

Which will capture the correct version in either case. The advantage is you do not need to know which match group to use -- the return is always group 1.

Demo

If you want to use the alteration form that you have, that can be refactored a bit as well to have a single capture group:

(?:Windows_|\S+OpenSSH_)(\d.\d)

Demo

Just know that format will have much more backtracking and may be 10x less efficient than the first form.