How to install Linux compatible apropos
No, it does not have to do with macOS having a &quot;BSD apropos&quot; and Linux having a &quot;Linux apropos&quot;.
Apropos on Linux and macOS is actually the exact same program. The difference you're seeing here is that macOS comes with a rather old version of apropros. You would find the exact same program in Linux distributions from that time period (at that time it was actually a rather simple shell script).
The &quot;-r&quot; option for regular expression was introduced with man-db version 2.5.4 from 2009, of which apropros is part.
You can install a newer version of man-db (and apropos) by having HomeBrew install, and running:
brew install man-db