Re: bin/47597: local and $() don't play well with each other

[David Laight <david%l8s.co.uk@localhost>]

On Fri, Mar 01, 2013 at 04:45:19AM +0700, Robert Elz wrote:

>   | Furthermore, this means that the behavior of an
>   | external utility and the behavior of the same made as a function will be
>   | different.
> 
> Yes, it does, and this is a problem, yet it seems to be intentional in 2.9.5
> (and from people who know from the opengroup list/newsgroup seems to have been
> intended because of how existing shells were implemented).
> 
> On the other hand, this contradicts 4.20 which requires that (aside from
> using tricks) there should be no way to detect whether a command is
> implemented as a function, built-in, or utility (note the special built-ins
> are not included in this relationship).
> 
> [Tricks mean things like measuring performance, and inferring whether a
> command is built-in or a utility from how fast it runs, or knowing the
> command search rules and inserting a script with the name of the command
> being tested in a directory at the start of $PATH - if the script is executed,
> then the command is a utility, if it is not, then it would be a function
> of built-in.]

The last one is allowed for, somewhere it says that the builtin version
should only be used if the one that would be executed (after searching
$PATH) is the one in the standard place.

Netbsd's /bin/sh doesn't do that check - I don't know if any other shells do.
It would remove a big chunk of the speed benefit of running the builtin.

        David

-- 
David Laight: david%l8s.co.uk@localhost