On Mon, Jun 10, 2019 at 8:56 AM Chet Ramey <[email protected]> wrote:
>
> On 6/10/19 11:38 AM, enh wrote:
> > the toybox project is adding a shell, and came across this issue that
> > i (Android native tools/libraries maintainer) have hit before because
> > mksh does exactly what POSIX says and bash does what POSIX probably
> > intended:
> > http://lists.landley.net/pipermail/toybox-landley.net/2019-June/010530.html
> >
> > repeated here, lightly edited and extended, because i know there are
> > plenty of shell folks here:
> >
> > I've reached the part of the posix shell stuff (section 2.9.1: simple
> > commands)
> > that specifies this behavior, and posix doesn't match bash:
> >
> > If no command name results, or if the command name is a special built-in
> > or
> > function, variable assignments shall affect the current execution
> > environment.
> > Otherwise, the variable assignments shall be exported for the execution
> > environment of the command and shall not affect the current execution
> > environment except as a side-effect of the expansions performed in step 4.
>
> This has been changed in the current published version of POSIX, which
> makes the variable persistance behavior unspecified:
>
> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_01
excellent!
> "If the command name is a function that is not a standard utility
> implemented as a function, variable assignments shall affect the current
> execution environment during the execution of the function. It is unspecified:
>
> Whether or not the variable assignments persist after the completion of
> the function
>
> Whether or not the variables gain the export attribute during the
> execution of the function
>
> Whether or not export attributes gained as a result of the variable
> assignments persist after the completion of the function (if variable
> assignments persist after the completion of the function)"
>
>
>
> >
> > A) This is not what bash does, or has ever done:
> >
> > $ hello() { echo boing=$BOING; }
> > $ BOING=123 hello
> > $ echo $BOING
>
> While this is true for bash in its default mode, bash implements the
> previously-mandated POSIX behavior in POSIX mode:
>
> $ cat x3
> set -o posix
> hello() { echo boing=$BOING; }
> BOING=123 hello
> echo after: $BOING
> $ ../bash-5.0-patched/bash x3
> boing=123
> after: 123
>
> I agree that the default bash behavior is more useful and often what is
> desired (that's why it's the default), and the next version of bash will
> probably make that the default in POSIX mode as well.
yeah, it also seems like the least surprising behavior... when i first
saw this with folks porting from bash to mksh to run on Android, i was
convinced it was a mksh bug because it didn't make any sense that
you'd get different behavior for a function than for an external
command!
> Chet
>
> --
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
> ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, UTech, CWRU [email protected] http://tiswww.cwru.edu/~chet/
