Way back in the middle 1990s, HP added the Posix shell to the HP 3000, so customers who had Unix and MPE running in the same shop could train operators and managers with a single set of commands. Posix was a plus, making the 3000 appear more Unix-like (which seemed important at the time).
It's been said that Posix was a promise only partly fulfilled for the 3000. There was a move to make the system more inclusive, to make it possible to port Unix software onto MPE/iX. Alas, a tech roadblock called the Fork of Death stood in the way of more widespread porting.
Over the years, however, Posix has been a feature to be discovered for most 3000 managers and operators. HP intended it to be essential; the computer's operating system was renamed from MPE/XL to MPE/iX just to call attention to these added Posix, Unix-like capabilities.
MPE failed in the Posix world primarily because of the unix "fork()" concept, so critical to the very nature of all that is Unix. It is a totally alien concept to MPE. MPE was designed to easily add additional new users to an executing process, and maintain the security/integrity of each individual user. It was not designed to duplicate a current process's environment, including the local data and state, because there was no point.
As one sage developer said of the deathly fork, "Yes, MPE would fork(), but very reluctantly, and very slowly. So nothing that depended on it worked very well."
But enough history; Posix is still on the 3000 and remains a powerful interface tool, an alternative to the CI interface that HP created for the system. You can even call Posix commands from the CI, a nifty piece of engineering when it can be done. That's not always possible, though. A customer wanted to know how to "expand wildcard shells" using Posix. He tried from the CI and had this story to relate.
ls: File or directory “/BACKUPS/HARTLYNE/S*” is not found
So how do I do this? I need to be able to tell tar to archive all of the reels of a STD STORE set via a regexp. It does not work in tar, and it apparently does not in ls, so I speculate that there is something special about the innovation of Posix utilities from the CI that I am not aware of. What is it?
Jeff Vance, the 3000 CI guru while at HP, who's gone on to work in open system and open source development, said this in reply:
Wildcards on most (all) Unix systems, including Posix implementations, are done by the shell, not the individual programs or in-lined shell commands, like ls in your example. A solution is to run the shell and execute ll from within.
Greg Stigers then supplied the magic Posix shell command to do the expansion:
SH.HPBIN.SYS '-c "/bin/ls -l /BACKUPS/HARTLYNE/S*"'
In a note of thanks, the customer said that getting the answer by working with the HP 3000 community's newsgroup "is like having an entire IT department right outside my door."
An interesting footnote if you've read this far: The Posix shell for the 3000 is one part of the operating system not built by HP. The shell was licensed by HP from MKS, and Hewlett-Packard pays royalties to MKS so Posix can work inside of MPE/iX.
For now, enjoy using Posix as a way to get familiar with the commands in Unix systems. In the great majority of instances, these commands are the same.