bug#23090: true and false not POSIX

[Paul Eggert]

On 03/22/2016 09:39 AM, Ruediger Meier wrote:
> You could also let true behave like rm if POSIXLY_CORRECT is not set or
> if more than zero option given.
This misunderstands the intent of POSIXLY_CORRECT. Setting 
POSIXLY_CORRECT does not mean "remove all extensions not specified by 
POSIX". It merely means "conform to POSIX even where the default is to 
not conform".

It might be helpful to have some other environment variable that meant 
"try to be strict about supporting only behavior required by POSIX", as 
one could use that to develop shell scripts that were more portable. 
However, that would be a lot of work to implement, and it's not clear 
it's worth the hassle to develop, maintain, and document. Plus, POSIX 
does not always specify behavior, so portability wouldn't be guaranteed 
by this.