The naming conventions are, at least in my opinion, easily confused. The use of spaces and capitalisation can make a lot of difference.

For versions where $^O returns MacOS, see perlmacos (that's the most recent online perldoc [for 5.26.1]). Note the versions of Perl where support was dropped and then removed. See perlport (5.8.9) > PLATFORMS > Mac OS for historical information (including use of the ":" separator).

Mac versions 10.x started roughly 20 years ago. They were originally called "Mac OS X". Around version 10.10 — I don't have exact information to hand — that became "macOS". (I don't know why.) They all use the "/" separator (same as any UNIX-like system).

I have personal knowledge of versions from 10.7 "Mac OS X" to 10.12 "macOS" (I've used most but not all). To the best of my knowledge, for all of these versions, $^O has always returned darwin. 

$ perl -le 'print $^O'
darwin

[download]

Unless support for very old hardware is intended, coding for $^O returning MacOS is probably unnecessary (except, perhaps, for a warning about an unsupported operating system).

— Ken

In reply to Re^3: What's your programming style? by kcott
in thread What's your programming style? by harangzsolt33

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