Re: variable set in exec'ing shell cannot be unset by child shell

[Martin D Kealey]

On Sun, 15 Oct 2023, 03:05 Greg Wooledge, <greg@wooledge.org> wrote:

> On Sat, Oct 14, 2023 at 12:55:21PM -0400, Ti Strga wrote:
> > it's just the "[[ -v foo ]]" tests to see where along the cloning
> process we are.
>
> *Shudder*
>

Likewise, brrrr.

If the *real* goal is to overwrite a running script with a new version of
> itself, and then re-exec it, then the correct solution is to wrap the
> script in a single compound command so that it gets read and parsed up
> front, before beginning execution of the main loop.  Either wrap the whole
> thing in "{" ... "}" as Grisha suggested, or wrap the whole thing in a
> "main()" function and then call main "$@".
>

Agreed. Either way, don't forget to put "exit;" just before the closing
"}". Or write « exec main "$@" ».

(For good measure I would also make sure it's a valid posix text file with
a terminal newline, so that cat rubbish >> script can't break it.)

Personally I don't much care for the main "$@" style as it makes an extra
copy of argv for no particularly good reason, and Shell Is Not C™; but it's
better than allowing the script to blow up with parse errors after it's
started running.

-Martin

>