X-Recipient:	archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status:	No, hits=-10.2 required=5.0 tests=AWL,BAYES_00,KHOP_PGP_SIGNED,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_DNSWL_HI,RCVD_IN_HOSTKARMA_W,SPF_HELO_PASS,TW_YG,T_RP_MATCHES_RCVD
X-Spam-Check-By:	sourceware.org
Message-ID:	<4F7C4CD2.3090005@redhat.com>
Date:	Wed, 04 Apr 2012 07:29:54 -0600
From:	Eric Blake <eblake AT redhat DOT com>
User-Agent:	Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1
MIME-Version:	1.0
To:	cygwin AT cygwin DOT com
Subject:	Re: Is this supposed to work this way?
References:	<0105D5C1E0353146B1B222348B0411A20A6536CB91 AT NIHMLBX02 DOT nih DOT gov> <602324786 DOT 20120404044708 AT mtu-net DOT ru> <4F7B9C81 DOT 4060209 AT redhat DOT com> <696106181 DOT 20120404053558 AT mtu-net DOT ru> <4F7BC6B1 DOT 8030506 AT etr-usa DOT com> <103388385 DOT 20120404130124 AT mtu-net DOT ru>
In-Reply-To:	<103388385.20120404130124@mtu-net.ru>
OpenPGP:	url=http://people.redhat.com/eblake/eblake.gpg
X-IsSubscribed:	yes
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com

--------------enigE86F55887B8901F4EA487E64
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

On 04/04/2012 03:01 AM, Andrey Repin wrote:

>=20
> Well, then, following your wisdom, I have to clog every line of my script=
 with
> "... || exit" or an equivalent.

No, you don't.  You can factor out your feature checks up front, in a
way that still works with 'set -e', rather than having to give up 'set
-e' through the entire script.  That said...

>=20
> Because even an attempt to continue execution, if any error occured, woul=
d be
> disastrous to the calling program.
> Solution is to "set -e" and have script bail out at any problem,

'set -e' is a can of worms, best avoided if you don't want surprises.
Consider:

f() { set -e; false; echo hi; }
f || echo bye

It does NOT exit on the false.  Rather, it prints 'hi' and NOT 'bye',
all while turning on set -e for the rest of your script.  And that
behavior is mandated by POSIX.  My opinion is that you are better off
coding without 'set -e' in the first place.

> but if I try
> autoconf approach and blindly run whatever I feel appropriate, hoping for=
 the
> best and preparing for worst, I won't have such option.

Give us more details of a feature you're trying to test.  I'll even get
you started with an example - suppose you want to know when to use cygpath:

if (cygpath --version) >/dev/null 2>&1; then
  my_convert() { cygpath "$1"; }
else
  my_convert() { echo "$1"; }
fi

foo "$(my_convert "$file")"

which will run cygpath on $file on cygwin, and will use $file unchanged
on other platforms.  And there you have a feature check - you checked
the feature of whether cygpath exists as an executable up front, then
the rest of your script is now OS-independent by relying on your
up-front setup based on the results of the feature check.

--=20
Eric Blake   eblake AT redhat DOT com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


--------------enigE86F55887B8901F4EA487E64
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
Comment: Public key at http://people.redhat.com/eblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iQEcBAEBCAAGBQJPfEzSAAoJEKeha0olJ0NqPXIH/1C06ywHdS9vWGtXsIDn0pQ0
i4Ma0xblxyLqy4OxX93n/ZF/lw8jNBHNrRVcKWYbQtbFrxw1jptqWhTpvQftXBO4
XpfV+W/yUUG22f9rtsviEpdN9yacI7ZAirOytTzJn+D1bLFohKXAQDt2z7ebRgnD
iifpPem0ea2YFc4FIpUBuGMZ4V4tA6rA4HNdjVXbTRgCWlg1M0jc90J7+SW6uyE+
yVxlLGe/h3EDJNj3IMZN+nDpAvBVlTUcN3p0ytB6iMlfTyO4jEhCvQjUhnsVHR97
NpC6YROQNYXk4VCRjcwrWJqlEZeD6SeNlDj+i+1Dw7V6hSYU9ZE781b3Ki1o+C4=
=t1f1
-----END PGP SIGNATURE-----

--------------enigE86F55887B8901F4EA487E64--

- Raw text -