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

[Chet Ramey]

On 10/14/23 12:03 PM, Robert Elz wrote:

> However in the case of a special built-in utility (which "." is) then
> the requirements are much stricter:
>
>    � If the command name is a special built-in utility, variable assignments
>      shall affect the current execution environment before the utility is
>      executed and remain in effect when the command completes; if an assigned
>      variable is further modified by the utility, the modifications made by
>      the utility shall persist. Unless the set -a option is on (see set),
>      it is unspecified:
>
>        -- Whether or not the variables gain the export attribute during the
>           execution of the special built-in utility
>
>        -- Whether or not export attributes gained as a result of the variable
>           assignments persist after the completion of the special built-in
>           utility
>
> That is, in the case of "VAR=val . script" (which is what the OP was doing,
> there were no functions involved) POSIX actually requires that VAR=val be
> done before the utility is invoked (and never undone) and that if the script
> modifies VAR, that modification remain after it has completed.

Special builtins are a POSIX concept, and bash conforms to POSIX when in
posix mode. It doesn't treat special builtins differently when not in
posix mode.


> Note that some of that text is new in Issue 8, to deal with making it
> clear what happens if a script does "X=Y unset X" where previously it
> might have seemed permitted for X to remain set after that command (to Y
> or whatever value it had before) - now it is (will be) clear that is not
> permitted, and X must be unset after that command completes. 

Bash doesn't do this yet in posix mode, but it will eventually.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/