Re: shell

On Mon, 27 Mar 2006 13:54:09 +0100, Geoff Clare wrote:
[...]
So, how do you force a XPG4 or XPG6 "conforming environment" in
a portable way? (based on a "case `uname`"?).

There is no portable way to set up a conforming environment from
a non-conforming one. (Nor could there ever be, if you think about
it, as the standards cannot place any constraint on the behaviour
of non-conforming environments).
[...]

But Solaris is meant to be conformant, isn't it? On startup, it
doesn't provide you with a conforming environment. So there has
to be a way to switch to that environment, otherwise, the
standard is rather pointless.

With Solaris 7, according to the standards(5) man page, it looks
like you only need to make sure /usr/xpg4/bin is before the
other ones to be SUSv2 conformant? What about Solaris 10, then.

So, if I want a SUSv2 conformant toolchest to interpret my
script written in a SUSv2 conformant syntax, practically, what
should I write:

#! /bin/sh -
if [ "$$" != "$FIND_SH_ACK" ]; then
FIND_SH_ACK=$$ export FIND_SH_ACK
case `uname` in
SunOS)
PATH=/usr/xpg4/bin/sh:$PATH
export PATH
exec /usr/xpg4/bin/sh - "$0" ${1+"$@"}
;;
Linux)
export POSIXLY_CORRECT=1 _POSIX2_VERSION=199210
;;
Tru64) ???;;
*) ???;;
esac
fi
unset FIND_SH_ACK

?

As far as the standard is concerned, the behaviour is undefined.
Utilities are only required to behave as described in the standard
if they are executed in a "conforming environment" (which includes
which environment variables are set among other things).
The suggested method (not yet implemented) in the link you
refered to:

env -i $(getconf V6_ENV) $(getconf PATH) command

(I suppose they mean
env -i -- $(getconf V6_ENV) "PATH=$(getconf PATH)" command

Environment variable names can't begin with dash, so the "--" is
unnecessary. You are right about PATH.

On which system can't environment variable names begin with "-"?

I agree it's very unlikely that getconf will return a variable
whose name doesn't only consist of uppercase
letters, digits, and the '_' (cf
http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html)
but the "--" can't harm there anyway.

Doesn't seem to work. First, there are issues with the current
value of IFS and globbing, and the second getconf will not be
run in a "conforming environment", so PATH may not be correct,
and it clears my environment, that's not what I want.

This is not a way of setting up a conforming environment, it is
a way of ensuring that enough of a current conforming environment
is inherited by commands started with "env -i" for them also to
be executing in a conforming environment.
[...]

OK, thanks.

--
Stephane
.