Don’t worship at the altar of portability. There is real cost to portability, as it forces you to cater to broken implementations and to not use features that may be very useful. Also, it can be difficult to ensure compatibility with systems that you don’t test on, so true portability requires having different systems to test on.
Sometimes all those costs are necessary for the task at hand. For example, the whole point of GNU Autoconf is that it runs on a wide variety of systems.
On the other hand, many programs are for in-house or personal use and will not run on obscure systems. The cost of writing for portability simply might not be worthwhile in these situations. And that’s ok, notwithstanding some conventional wisdom of “always try to be portable.”
Sometimes all those costs are necessary for the task at hand. For example, the whole point of GNU Autoconf is that it runs on a wide variety of systems.
On the other hand, many programs are for in-house or personal use and will not run on obscure systems. The cost of writing for portability simply might not be worthwhile in these situations. And that’s ok, notwithstanding some conventional wisdom of “always try to be portable.”