This is why i f**ing hate macOS. Developers wax poetic about 'oh its a UNIX', but NOTHING works like Linux once you dig into it. Zsh is different from bash, subtle API differences, different filesystem, esp with stuff like /dev or /proc or /etc, no systemd, some cli utils have different flags, subtle differences like this.
At least Windows is completely different and there's no expectation of compatibility, but with the mac you can start off thinking things would work, but they don't.
Some of the things you point out here are things you cannot rely on in Linux consistently, either.
You can’t rely on Systemd existing in Linux. You can’t rely on bash being the shell in Linux. Depending on the users system and distribution these tools may or may not exist.
Also the difference in some of the tools CLI flags wind up boiling down to being the BSD versions of them as opposed to the GNU versions of them. Which, again, isn’t a problem isolated to MacOS.
If you’re considering all Unixes everything you said basically still applies even if you remove MacOS from the equation. Unix isn’t just Linux.
The only practically relevant Linux environments you can't expect these things to exist are stripped down distros used for docker images, like Alpine (where you don't expect much from the system anyways) and Android (not sure about the latter, haven't used it in production in quite a while, but afair it's as non-standard as it gets).
Ubuntu has had a non-Bash system shell (dash is /bin/sh) since 6.10.
> no systemd
Without getting into objected-on-principle distributions like Devuan, tons of stripped-down and embedded linux distros besides Android and Alpine don't have systemd, e.g. DD-WRT, OpenWRT, TinyCore. Heck, launchd is more similar to systemd than SysV init was.
> /dev or /proc or /etc
Other than the parts specified by POSIX, the /dev filesystem is the wild west across tons of Linux and Unix systems, and expecting further standardization in behavior from it is a fool's errand (e.g. device name selection, device ID assignment order at boot, presence of metadata-symlinked directories like by-id, overlay/loopback devices ... all of these are highly variable even across modern, systemd-using Linux distros). I do miss /proc, though I don't miss the file descriptors it costs. /etc and XDG standards for configs are nice conventions to be sure, but a significant minority of Linux software breaks with those conventions (all-/opt install locations, anyone?).
> different filesystem,
Sure, APFS isn't ext3/4. Neither are XFS, ZFS, BTRFS, and so on. ext3/4 is a tenuous standard at best, and many businesses make a point of preferring other filesystems on Linux.
...like, I think you might have just been getting lucky and using a fairly similar set of Linux distros such that MacOS was a big switch. There are plenty of valid beefs with MacOS's divergences (don't get me started on an OS that claims certified POSIX compliance while providing a plethora of low-level system APIs documented to break in the presence of fork(2), or the not-quite-superset clusterfuck that is FSEvents vs. MacOS's not-quite-BSD-complete kqueue implementation, or the Sophie's choice of bizarre xattrs behavior vs. the historical accident that is aliases), but what you listed isn't even remotely standard Linux behavior, much less Unix behavior.
Tip: when a greyed out comment is difficult to read, click on its timestamp. That will open a view on just that comment and its replies and it will not be greyed out in that view.
That's a weird objection. Linux isn't UNIX, technically. All of the current and former UNIXes had various incompatibilities. /proc was never standardized. /dev has some standard names, but not many. Not sure what you mean about /etc, that's up to whatever's installed in userland. systemd is more or less Linux only; it's weird to blame other OSes for not having it. (The funny thing is that systemd has functionality in part inspired by macOS's launchd.) The ext* family of filesystems (and certainly stuff like btrfs) is a Linux thing; other UNIXes used different file systems.
CLI utils are an interesting thing: the BSDs have always(?) had their own, and don't use GNU coreutils (which is what Linux uses). There wasn't really much coordination over the decades, so they went in different directions. Most (all?) of them should be POSIX-compliant (possibly after setting an env var, at least in GNUs case), so if you restrict yourself to functionality specified in POSIX, you should be fine.
I don't really like macOS, but your specific criticism of it doesn't really hold water. If you're going to hate on macOS for this stuff, then you also have to hate on all the BSDs, which seems a little silly and unwarranted.
> with the mac you can start off thinking things would work, but they don't.
If you're expecting things to work on macOS just like on Linux, then your expectations were way off in the first place. If you want cross-platform compat in these areas, you'll have to stick with POSIX. Which sucks, especially since no one really implements POSIX correctly, but that's just how it is, and has always been.
Having used hp-ux, sunos, solaris, aix, plan 9, various flavors of linux and a bunch of embedded OSs, VMS, and various Windoze systems I formally welcome you to the Real World.
The Real World - it's got more stuff than you can imagine.
This is false plurality - while some bank or legacy datacenter might have these OSes in production, 99% of the time, you'll only encounter Linux in a professional server environment (or the Real World as you call it).
How does that matter, though? You're complaining that macOS is different from Linux. That's the salient point. And, duh: they're different OSes. macOS is just as different from Linux as any other OS out there is. And macOS is closer to Linux than some (like Windows).
You initially said, seemingly implying this was a "false cool thing":
> Developers wax poetic about 'oh its a UNIX'
I don't think they meant what you think they meant by that. When people said that (back in the early '00s), people were familiar with Linux, yes, but they also interacted with several other commercial UNIXes that were still in wide use at the time (like those mentioned by the GP), as well as the BSDs. Being able to treat macOS like a UNIX (or, more specifically, like a BSD) was a big step up in convenience from Mac OS Classic.
No one expected macOS to be like Linux, at least not in the ways you are talking about.
Indeed, I've been Linux-only for a bit over 10 years now, and when I have to do some work on a Windows or Mac for work, Windows with WSL feels a lot better than modern macos. You'll encounter the occasional alien thing when Windows details leak through, but for the most part it just behaves like you expect. If I had to pick a mac or windows pc for daily driver, Windows would be an easy choice now (although as coming of age in the 90s when MS was evil, it's mind-blowing to hear me say this all!)
At least Windows is completely different and there's no expectation of compatibility, but with the mac you can start off thinking things would work, but they don't.