Re: documentation around RE repetition metachars may need clarification

[Andrew J. Schorr]

Hi,

On Sun, May 21, 2023 at 09:46:50AM -0500, Ed Morton wrote:
> In the gawk manual under 
> https://www.gnu.org/software/gawk/manual/html_node/Regexp-Operator-Details.html
> we have this statement:
> 
> >In POSIX |awk| and |gawk|, the ‘*’, ‘+’, and ‘?’ operators stand
> >for themselves when there is nothing in the regexp that precedes
> >them.
> 
> while in the POSIX spec under 
> https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_03
> we have this statement:
> 
> >*+?{
> >    The <asterisk>, <plus-sign>, <question-mark>, and <left-brace>
> >    shall be special except when used in a bracket expression (see RE
> >    Bracket Expression
> >    
> > <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05>).
> >    Any of the following uses produce undefined results:
> >
> >     *
> >
> >        If these characters appear first in an ERE
> >
> 
> So the gawk manual statement says that /+foo/ in any POSIX awk will
> match the literal string "+foo" while the POSIX spec statement says
> it's undefined behavior.
> 
> Should the gawk manual be tweaked to clarify/explain what it
> currently says about POSIX awk since it apparently contradicts the
> POSIX spec?

Stupid question: when something says that the behavior is undefined, is
it not the case that a given implementation is entitled to make its
own choice about how to handle that situation? If so, why is gawk's
choosing to match "+foo" at odds with POSIX? If it's "undefined", do
you instead expect it to throw an error?

Regards,
Andy