A typical construct is
if [[ -z $LD_LIBRARY_PATH ]]; then
export LD_LIBRARY_PATH=$MYLIB
else
LD_LIBRARY_PATH=$MYLIB:$LD_LIBRARY_PATH
fi
I could replace this with
export LD_LIBRARY_PATH=$MYLIB${LD_LIBRARY_PATH:+:}${LD_LIBRARY_PATH-}
but so far I haven't seen this construct in any script.
Using the -v <name> extension of test conditions
if [[ -v LD_LIBRARY_PATH && -z $LD_LIBRARY_PATH ]]
is not portable and more work than using
if [[ -z ${LD_LIBRARY_PATH-} ]]
An extension which I would like to see is an additional option -U which works
like -u but replaces $VAR by ${VAR-} after -n and -z in test conditions.
Best Regards
Axel PHILIPP
MTU Aero Engines AG
Von: Janis Papanagnou [mailto:[email protected]]
Gesendet: Mittwoch, 16. Oktober 2013 14:56
An: PHILIPP, Axel, Dr.
Cc: [email protected]
Betreff: RE: [ast-users] Question about the nounset option
I understand the OP considering that clumsy. And something being defined
by POSIX doesn't prevent it being clumsy or not defined in an optimal way;
sometimes even the opposite is true. But I'd rather like to abstain from such
flame-prone valuations and consider the given application.
@Axel: I'm not sure your sample is only test code. If so, you can trigger the
effecte more simply (without if condition) by /bin/ksh -uc 'echo ${TESTVAR}'.
Otherwise I'd use the less clumsy /bin/ksh -uc 'echo ${TESTVAR-"undefined"}
(without if, but still with the default value substitution).
Part of the clumsiness in your sample stems from the explicit if test and the
implicit test in ${v- }; one can be avoided.
Janis
> Date: Wed, 16 Oct 2013 14:23:57 +0200
> From: [email protected]
> To: [email protected]
> CC: [email protected]
> Subject: Re: [ast-users] Question about the nounset option
>
> On 16 October 2013 09:14, PHILIPP, Axel, Dr. <[email protected]> wrote:
> > I wonder whether it is desirable that test -n and test -z trigger the unset
> > error condition:
> >
> > /bin/ksh -uc 'if [[ -n $TESTVAR ]]; then echo $TESTVAR; else echo
> > "undefined"; fi'
> > /bin/ksh: TESTVAR: parameter not set
> >
> > I know all shells from the sh family I have tested behave this way, but I
> > would prefer a solution (additional option or env var) that the error is
> > not triggered in these test cases.
>
> You can use [[ -v TESTVAR ]] to test whether a variable does exists or
> not. This uses the variables name (TESTVAR) and not the value
> ($TESTVAR).
>
> >
> > The obvious workaround is somewhat clumsy:
> > /bin/ksh -uc 'if [[ -n ${TESTVAR-} ]]; then echo $TESTVAR; else echo
> > "undefined"; fi'
> > undefined
>
> Why is this clumsy? This is how POSIX sh was designed and everyone
> uses as designed. Why is this a problem?
>
> Lionel
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