Find the exact Build Number of a specific Mac OS X update from the command line

New Contributor II

How do I find the System Build Number or I guess it is called just the Build Number (example 18A391 or 18G87 or 18G5033 or etc. etc.) for a specific Mac OS X updates? Not upgrade, just the regular updates. Examples: Supplemental or Security or Combo or Safari, etc. etc.

I am aware of thousands of blogs and websites that published those type of information's, but let's do a practical example:

Step #1 I download this specific dmg file (Security Update 2020-006 (Mojave)) from:

Step #2 I mount the dmg file and I extract the pkg file.

Now, I do believe that the pkg file that I just extracted from the dmg file it is some sort of xar archive file, so my question is:

using the command line, how do I unzip the xar archive file and after I unzip the archive, what specific plist file I am looking for in order to find out the exact Build Number of this specific Security Update 2020-006 update?

Thank you