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From: Icarus Sparry on 14 Dec 2009 13:45
On Mon, 14 Dec 2009 17:28:39 +0000, Dave wrote:

> Icarus Sparry wrote:
>> On Mon, 14 Dec 2009 17:05:52 +0000, Dave wrote:
>>
>>> I have a shell script written by someone else, which starts
>>>
>>>
>>> #!/usr/bin/env bash
>>>
>>>
>>> then has the line:
>>>
>>> unset DISTUTILS_DEBUG
>>>
>>> It's a bit pointless, as DISTUTILS_DEBUG is not set in the script, but
>>> there is some code commented out, where is was obviously set at one
>>> time.

> bash-2.04$ bash --version
> GNU bash, version 2.04.0(1)-release (hppa2.0w-hp-hpux11.00) Copyright
> 1999 Free Software Foundation, Inc. bash-2.04$
>
> Is this likely to be a problem with HP-UX, or bash? The bash command is
>
> /opt/OpenSource/bin/bash
>
> so from the location, one might guess HP do not support 'bash'
>
> I appreciate a newer version of bash might not suffer this problem, but
> I'd rather sort out issues which occur with old versions of commands too
> - not everyone runs the latest. The code I am using is checked by quite
> a few people on the more common linux and OS X distributions, so most
> people will not find issues like this.

By an unhappy chance I happen to have a bash-2.04 system at hand, and it
also returns '1' if you unset a variable that is not set, so it looks to
be a bash bug.

bash 2.04 dates from March 2000.

If you remove the "set -e" that you added then there would not be an
issue. You could put a "set +e" and "set -e" pair around the "unset" as
another way to work around the issue.
From: OldSchool on 14 Dec 2009 14:31
>> Is this behavior to be expected? It does not happen under OS X, Linux or
>> Solaris, but is causing a problem on HP-UX 11.11.

>>
>>
>> Dave
>>
>>
>
> Looking at POSIX 2004,
>
> http://www.opengroup.org/onlinepubs/009695399/utilities/unset.html
>
> it says:
>
> "Unsetting a variable or function that was not previously set shall not be
> considered an error and does not cause the shell to abort."
>
> so it looks like this is a place where HP-UX is not POSIX 2004 compatible.
>

I'd be more inclined to say that the version of the bash shell installed on
the HP-UX system is not compliant. HP doesn't ship bash with HP-UX, so
somebody added it to the system in question. as Icarus noted, this is a
very old version, and it probably should be updated.

From: Stephane CHAZELAS on 14 Dec 2009 15:09
2009-12-14, 17:05(+00), Dave:
[...]
> unset DISTUTILS_DEBUG
>
> It's a bit pointless, as DISTUTILS_DEBUG is not set in the script, but there is
> some code commented out, where is was obviously set at one time.
>
> I've added
>
> set -e
[...]

That was fixed in bash-2.05b-beta1. 2.05b was released in 2002.
The latest version of bash is 4.0.35. You may want to consider
upgrading.

--
St�phane
From: Stephane CHAZELAS on 14 Dec 2009 15:16
2009-12-14, 17:20(+00), Icarus Sparry:
[...]
>> unset DISTUTILS_DEBUG
[...]
> The normal way is to use the
> ${DISTUTILS_DEBUG+yes}
> variable expansion. This will evaluate to "yes" if the variable is set,
> even if it is the zero length string, and nothing otherwise.
>
> So hopefully
> test -z "${DISUTILE_DEBUG+yes} && unset DISTUTILS_DEBUG
> will fix your problem. What version of bash are you running on your HP-UX
> machine?

The common way to make a command immune to set -e is to write
it:

unset DISTUTILS_DEBUG || : OK

Best is not to use "set -e" and add "|| exit" where relevant
(or any other corrective/alternative action, or use if/then...).
The behavior of set -e is not consistent from one shell to the
other and is hard to guess intuitively in corner (and not so
corner) cases (as in subshells, pipes, functions, compound
commands, dotted scripts...)


--
St�phane
From: Dave on 14 Dec 2009 17:01
Stephane CHAZELAS wrote:
> 2009-12-14, 17:05(+00), Dave:
> [...]
>> unset DISTUTILS_DEBUG
>>
>> It's a bit pointless, as DISTUTILS_DEBUG is not set in the script, but there is
>> some code commented out, where is was obviously set at one time.
>>
>> I've added
>>
>> set -e
> [...]
>
> That was fixed in bash-2.05b-beta1. 2.05b was released in 2002.
> The latest version of bash is 4.0.35. You may want to consider
> upgrading.
>

I could easily upgrade - in fact, there is a later version someone else built on
the machine.

But it does no harm to find out issues that arise as a result of using older
versions of software. The release of HP-UX is quite old, but it is the latest
which will work on the PA-RISC processor. The newer releases only work on Itanium.

Dave

--
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