Unsetting a variable that was not previously set

Unsetting a variable that was not previously set

[Vincent Lefevre]

zsh should return an exit status 0 when unsetting a variable that was
not previously set.

greux:~> zsh-beta -f
greux% echo $ZSH_VERSION
4.1.0-dev-7
greux% unset blah && echo OK
greux%

It should have printed 'OK'.

See
  http://www.opengroup.org/onlinepubs/007904975/utilities/unset.html

"Unsetting a variable or function that was not previously set shall
not be considered an error and does not cause the shell to abort."

The following shells print 'OK' as expected:
  * /bin/sh under Solaris
  * /bin/sh under OSF1
  * bash (under Linux)

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/> - 100%
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Work: CR INRIA - computer arithmetic / SPACES project at LORIA

Re: Unsetting a variable that was not previously set

[Peter Stephenson]

Vincent Lefevre wrote:
> zsh should return an exit status 0 when unsetting a variable that was
> not previously set.
>
> See
>   http://www.opengroup.org/onlinepubs/007904975/utilities/unset.html

I think you're probably right, but it's not completely clear.  The page
you quote explicitly says:

EXIT STATUS

     0
        All name operands were successfully unset.
    >0
        At least one name could not be unset.

Now, if it doesn't exist, it can't be unset, but I think by `unset' they
mean `rendered such that it is not set whether or not it was before',
which is your interpretation.

> "Unsetting a variable or function that was not previously set shall
> not be considered an error and does not cause the shell to abort."

It doesn't cause the shell to abort currently.  The terminology in the
introduction does suggest `error' is more or less synonymous with
`non-zero return code', but I can find no normative indication of
whether this applies to the language used for the special builtins.

Probably someone should request a clarification.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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Re: Unsetting a variable that was not previously set

[Oliver Kiddle]

Peter wrote:
> Vincent Lefevre wrote:
> > zsh should return an exit status 0 when unsetting a variable that was
> > not previously set.
> >
> > See
> >   http://www.opengroup.org/onlinepubs/007904975/utilities/unset.html
> 
> I think you're probably right, but it's not completely clear.  The page
> you quote explicitly says:

I queried Chet about this when it was changed in bash (about a year
ago) and got this response:

    I got a bug report or two, and decided that the new behavior is
    what POSIX.2 intended.  It seems to be what sh has always done.

    It's still open to debate, though.  I can be convinced otherwise.

I never made up my mind to do anything in part because ksh93 does the
same as zsh but it is probably right. Also, at the moment, it seems
that for an readonly variable, it is returning 0 which is clearly
wrong.

> Now, if it doesn't exist, it can't be unset, but I think by `unset' they
> mean `rendered such that it is not set whether or not it was before',
> which is your interpretation.

It seems a fair interpretation. Perhaps could be wise to have it
clarified though.

Oliver

Re: Unsetting a variable that was not previously set

[Vincent Lefevre]

On Fri, Apr 04, 2003 at 17:09:49 +0100, Peter Stephenson wrote:
> I think you're probably right, but it's not completely clear.  The page
> you quote explicitly says:
> 
> EXIT STATUS
> 
>      0
>         All name operands were successfully unset.
>     >0
>         At least one name could not be unset.
> 
> Now, if it doesn't exist, it can't be unset,

I don't think that a variable needs to exist in order to be unset.
I think that 'unset' is just a special status (or "value") for the
variable (a bit like 'undef' in Perl). So, we have the following
interpretation:

> but I think by `unset' they mean `rendered such that it is not set
> whether or not it was before', which is your interpretation.

and I think that this is the goal of the following sentence to make
things clear about this problem:

> > "Unsetting a variable or function that was not previously set shall
> > not be considered an error and does not cause the shell to abort."
> 
> It doesn't cause the shell to abort currently.  The terminology in the
> introduction does suggest `error' is more or less synonymous with
> `non-zero return code', but I can find no normative indication of
> whether this applies to the language used for the special builtins.

I could only find

  http://www.opengroup.org/onlinepubs/007904975/utilities/xcu_chap01.html

Under "EXIT STATUS": "Usually, utilities return zero for successful
completion and values greater than zero for various error conditions."

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/> - 100%
validated (X)HTML - Acorn Risc PC, Yellow Pig 17, Championnat International
des Jeux Mathématiques et Logiques, TETRHEX, etc.
Work: CR INRIA - computer arithmetic / SPACES project at LORIA