Okay. Care to point us all to the official standard POSIX flags documentation? Even then, you are probably going to find that there are just as many systems that your script needs to run on that are POSIX incompatible as there are systems that don't recognize the long flags.

My ultimate rule: write the code that is the most readable, because in 10, 15, 30 years, someone can easily update a script to working arguments from arguments with long words, whereas single letter arguments may have multiple different meanings on different systems. It's the same with naming conventions and code constructs: the how and the what should be obvious from the code.