UNIX for Beginners Questions & Answers

Yes, /usr/bin/perl -> perl5 should be everywhere. But do not expect certain perl modules!

When I was working at Sun, you could set PATH to include various *bin directories in various different orders to get an environment that met the requirements of several standards including (but not limited to) SVID3, XPG3, XPG4, XPG5, SUSv1, SUSv2, each of the revisions of the POSIX.1 and POSIX.2 standards (and most of the other POSIX standards except for POSIX.3), and also some versions of BSD and UNIX System V.

I make no claims about what has happened to that guaranteed backwards compatibility between releases since Oracle bought out Sun. (It may still work, I just don't know.)

If you don't consider shell and awk to be programming languages, the POSIX standards do still provide the C programming language. The current version of the POSIX standards are built on top of the 1999 ISO C Standard. The next revision of the POSIX standards will be built on top of the 2011 or 2017 C standard (depending on whether the Austin Group or the ISO C committee gets their next revision ready first. At one time there were POSIX working groups working on Ada and C++ bindings to POSIX.1, but those groups are no longer active. The Austin Group does still work closely with both the ISO C and ISO C++ working groups and although there is no C++ compiler specified in the POSIX.2 standard, the ISO C++ standard libraries are intended to be fully compatible with the POSIX.1 standards.

I was once offered up as a sacrificial lamb to attend some meetings helping to define standards for the Linux operating system. I was immediately deemed to be an enemy of everything that committee wanted to do. I believed that standards were created to help users write portable code; everyone else in the room thought standards were written to constrain operating systems development. Where the SVID, XPG, SUS, and POSIX standard specified requirements that conforming operating systems had to supply; the LSB (Linux Standards Base) went a different way. The LSB defined the names of some functions that the Linux operating system had to supply, but only gave very brief descriptions of what those functions did. The definition of how those functions behaved is defined by the source code for the Linux operating system; not by any document that an applications programmer could use to determine how to write a portable application that would run on any Linux system. If you write an application that conforms to the LSB and it works on one Linux system today, there is no guarantee that it will work on any Linux operating system tomorrow.

That was twenty-five years ago. Today, some Linux vendors actively participate in the Austin Group and try to mostly comply with POSIX requirements. (Note mostly; not completely. No Linux vendor has gotten a POSIX or UNIX certification demonstrating that their implementation passes the verification suites testing conformance to the POSIX standards nor the Single UNIX Specifications yet.)

Note that all of the above is my own biased opinion. Other people may well have different opinions.

Thanks all for the participation.

I hope I did not make my statements in the way they are the truth, but just did show them as my own preferences(e. g. the statement that "Shell scripting is now programming language") . Others may have other preferences. (@Bakunin: I'm sure you have a great script library of portable scripts he can use when he needs them in any environment).

In overall my views have not changed. Portability may be an important goal in writing scripts. But one does not get it for free. And it's not cheap, because it impacts other objectives one might have in programming, which may be...
But one can do easy things to keep portability and need not to break it lightly (Using BRE instead of ERE,...).

Despite being a bit interested in standardization, I was only reading news about that topic here and there. Thanks for the details Don. I gave up on that 20 years ago. Linux is absolutely great in terms of standardization like every distribution has it's own standard. (See xkcd: Standards). Just kidding. The linux folks are not even able to get together in which file the hostname of the system should reside. In the end the decision was made by using systemd which had it at the fixed location /etc/hostname.

In all my time it has never come to a common way e. g. to configure persistent networking. There are about 50 different ways to do it.

I do not know that. But I assume, you know what you are speaking of. The question for me is, what is needed as a runtime which is needed as a base - as a compatibility layer. I think it's not that good to have 100 GB of every possible and well working programming language installed in every system. I would rather like to have that base not too fat.