Unless you count things like Makefiles, I don't think I've ever written or encountered a "script" that was intended for use on multiple *nix flavors. This strikes me as a YAGNI situation: do it if it comes up, but not before.
Though sometimes you don't need to go that far to break stuff, for instance switching from Fedora to Ubuntu. I've seen many scripts fail on debian derivatives because people think using #!/bin/sh as a shebang is fine since it works on their computer where sh was in fact a symlink to bash.
But on debian based distributions /bin/sh is often dash, not bash, and dash is basically the strict POSIX subset + local, all fancy stuff like [[ ]], &>, arrays, ... will fail.
Though this is less about long options here and more about general shell scripting.
But, still, that's no reason to adopt a mindset of actively wrecking the chances of such success.
(Which is what passive ignorance amounts to, effectively).
It's not difficult to do, but it is annoying. I don't blame people for ignorance, but it'd be nice if people thought about portability.
Non-portable scripts can also bite you on Linux, where Debian, for example, will swap out the shell from bash to dash for performance. but others will not. So, even within the Linux ecosystem, you can end up with scripts that behave differently across distros.
From the bash man page, "If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible, while conforming to the POSIX standard as well." Also you should not be including bashisms if your shebang is sh and not bash. So using bash as sh shouldn't generally be a problem, if you stick to the published Shell Command Language [0], unless you hit one of the cases where the spec is a bit ambiguous and shells implement it differently [1].
[0] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V... [1] https://stackoverflow.com/questions/16069339/different-pipel...
From what I remember, it doesn't do a particularly good job.
And, again, this still bites whenever using different linux distros.
#!/bin/bash
#!/usr/bin/env bashHomebrew comes to mind, and any other piece of software that does the installation via a shell script.