I run a script with the nounset (-u) option if I suspect that an unset variable
may be used. The typical way to trap such a situation is to use a construct
like 'if [[ -n $VAR ]]; then ...', but I do not want to find all those traps
when I use the -u option.
I do not believe that I am the only one who does not use ${VAR-} which means
'if VAR is unset use an empty string instead'. But I would have to change all
occurrences to be able to use the -u option for debugging purposes.
I do not want to use [[ -v TESTVAR ]] because it is a ksh93 only extension.
Mit freundlichen Gruessen / Best Regards
Axel PHILIPP
MTU Aero Engines AG
mailto:[email protected]
-----Ursprüngliche Nachricht-----
Von: Lionel Cons [mailto:[email protected]]
Gesendet: Mittwoch, 16. Oktober 2013 14:24
An: PHILIPP, Axel, Dr.
Cc: [email protected]
Betreff: 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
--
MTU Aero Engines AG
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Eberhardt
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