Re: support for POSIX 1003.1-2001 hosts

> From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
> Date: Mon, 11 Mar 2002 19:04:24 -0500 (EST)
>
> The patch basically takes:
>
> sort +1 -0 and changes it to
>
> and makes it:
>
> sort +1 -0 || sort -k 1,0
>
> or something like that.

Here is a bit more detail about what the patch does.

* It transforms `head -1 FOO' to `sed q FOO'.
This is portable to all hosts that I know of.
As it happens, `head -1' didn't work in Unix Version 7, but `sed q' did,
so this transformation improves portability to some ancient hosts too.

* It transforms `sort +0n -1' to `(sort -k 1,1n 2>/dev/null || sort +0n -1)',
and similarly for all other uses of `sort +FOO'. The basic idea is
to try POSIX standard syntax (standard since the first version of POSIX,
anyway, more than a dozen years ago), and to fall back on the traditional
Unix Version 7 syntax if the POSIX standard syntax is not supported.

The former transformation is perfectly safe. The latter
transformation is a bit tricky, since the first `sort' can fail for
reasons other than "I don't know what -k is", and in that case the
second `sort' will be invoked even though it should not be. I don't
think this will be a real problem in practice, but if you're worried
about it I could change the second transform to look like this:

if sort -k 1,1n /dev/null >/dev/null 2>&1
then sort -k 1,1n
else sort +0n -1
fi

I can submit a revised patch along those lines if you like.