Re: Use of double parentheses

[Eric Blake]

On 07/31/2011 06:13 AM, Julien ÉLIE wrote:
> Hi all,
>
> Reading a generated "configure" file, I see:
>
> # Unset variables that we do not need and which cause bugs (e.g. in
> # pre-3.0 UWIN ksh).  But do not cause bugs in bash 2.01; the "|| exit 1"
> # suppresses any "Segmentation fault" message there.  '((' could
> # trigger a bug in pdksh 5.2.14.
> for as_var in BASH_ENV ENV MAIL MAILPATH
> do eval test x\${$as_var+set} = xset \
>    &&  ( (unset $as_var) || exit 1)>/dev/null 2>&1&&  unset $as_var || :
> done
>
>
> Wouldn't it mean that all '((' present in the "configure" script, and
> related to shell commands, should be rewritten to '( ('?

It's not a bug in pdksh - POSIX was recently reworded to allow (( to 
introduce arithmetic parsing on any shell that wants to provide it as an 
extension.  So yes, all instances of needing a double sub-shell MUST 
separate the two ( to comply with POSIX.

But unless you can point out any other instances of a double sub-shell 
in configure, I think we're okay on not tripping over this issue any 
where else.

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org