Re: posix command search and execution

[Chet Ramey]

On 11/7/23 5:04 PM, Mike Jonkmans wrote:

> >    | > 1d) Lists 20 fixed utility names (like alias, cd etc.) that are
> >    | >      to be invoked at his point. No PATH search yet.
> >    | >       These are the `regular builtins'.
> > In the next standard the ones listed are the intrinsic builtins,
> > and includes only those that must be builtin to work.   But
> > implementations can add more to the list.
>
> Chet mentioned that. But I find the Austin-discussion hard to read.
> It makes sense to partition the builtins in three categories with
> a separate name for each.

It depends on your requirements. If you want something that is easy to
explain to users, you want to reduce the distinction between `intrinsics'
and `regular builtins' to something as small as possible. That way the
search reduces to

special builtins*
functions
intrinsics
executables

in that order, with ways to override each one (except special builtins
in posix mode).

> >    | > 1eI) Search is successful.
> >    | > 1eIa) Check for `regular builtins' and functions
> >    | >       and invoke that regular builtin/function.
> >    | >       Q: Shouldn't this specify an ordering for builtins/functions?
> >    | The text seems to imply that you can't have both, doesn't it?
> > While I suppose you could have both, it would be very unusual.
>
> Unusuality sketch:
> - the shell provides a builtin for a standard utility
> - the distributor provides a function for the same utility in /etc/profile
>    (maybe to mitigate some security issue)
>
> Are scripts in /etc/profile considered part of the implementation?

Yes. But there's no way to make a distinction between this type of function
and any other user-supplied function, so the distinction isn't useful.


> >    | Note that this seems to require that you can only run
> >    | a builtin if it exists (or something with that name exists) in $PATH.
> > A builtin for a standard utility, yes. 

The standard doesn't explicitly make that distinction.


> I already can't find the definition of standard utilities.

The standard utilities are the ones specified in the standard.



> >    | I think the resolution to interpretation 854 addresses this. Shells
> >    | who want this ordering just declare all the builtins they implement as
> >    | `intrinsic' so they're not subject to a PATH search.
> > Yes.
>
> Can this intrinsic list be amended with any user loaded builtins?

You mean enable -f? It's up to the shell implementation. Bash treats
dynamically-loaded builtins the same as any other builtin.

--
``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/