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 <gaze...@xmission.com>
>     Message-ID:  <e1uvsmj-00000009afv-1...@shell.xmission.com>
> 
>   | 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.

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