On Sun, Jun 29, 2025 at 21:51:52 +0700, Robert Elz wrote:
> Date: Sun, 29 Jun 2025 08:13:07 -0600
> From: Stan Marsh <[email protected]>
> Message-ID: <[email protected]>
>
> | So, is this POSIX, or just a dash-extension?
>
> It is original Bourne Shell (from 7th edition Bell Labs Unix)
> and is (or should be) supported by every Bourne-compatible shell.
>
> It definitely is in POSIX.
In fact, the colon-less forms ${var-word} and so on were the originals.
The colon variants ${var:-word} were added later, IIRC by ksh.
See <https://www.in-ulm.de/~mascheck/bourne/v7/> for a Bourne shell
man page, showing ${parameter+word} and so on.
