cc: [email protected]
Subject: Re: [ast-users] ksh: `typeset -r var' sets `var' to Null if it is an
exported parameter from a parent shell
--------
> I stumbled over this behavior:
>
> from another shell (tcsh in my case) call ksh after first exporting some
> parameter from tcsh, i.e. in a running tcsh do
>
> % setenv a 123
> % ksh
>
> within the called ksh one gets of course
>
> echo $a # -> 123
>
> but after
>
> typeset -r a
>
> one gets
>
> echo $a # -> Null.
>
>
> I suspect the `typeset -r a' somehow masks the exported parameter of the
> same name which is such lost forever within the running ksh?
>
> question 1: is this behavior intentional? in bash and zsh `a' maintains
> its original value, which is what I would have expected in ksh, too.
>
> question 2: what is the best way for testing whether a parameter is
> readonly? I came up with
>
> s=$(typeset -r)
> ([[ -z "$s" ]] || [[ -n "${s/@(*$'\na'|a)=*}" ]]) && typeset -r a=$a
>
> (which checks if there are any readonlys at all and if so if parameter `a'
> is actually part of them)
> in order to enforce a readonly parameter with the original value. seems to
> be correct but is probably way too complicated.
>
> thanks
> joerg
>
> ps: oberved with 93u.
>
I was able to reproduce this with ksh93u but not with ksh93u+ which should
be available shortly. Therefore, it is fixed in ksh93u+.
David Korn
[email protected]
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