Paul Eggert <yyyyyy@xxxxxxxxxxx> wrote, on Sat 24 Mar 2001:
>
> Here's an example of why Solaris 8 find's behavior is incompatible
> with the current POSIX standard:
>
> find / -prune -exec echo {} + - ';'
>
> POSIX requires this to print "/ + -" but Solaris 8 find prints an
> error diagnostic instead.
It was this very issue that prompted me to start the discussion. I was
contemplating filing a POSIX.2 interp request asking whether the SVR4
use of "+" is a valid extension. But when I started to think more
about it, it seemed like the problem was really that there is a gap in
the standard, and that standardizing the SVR4 behaviour would be a
neat way of fixing both the question mark over its legality and the
problem with the standard. (Then I realised that GNU's -print0 is an
alternative solution to the same problem...)
> Admittedly this is a contrived example but
> I can see the possibility of real scripts running into compatibility
> problems with this incompatible change to "find".
It appears that the "+" is only treated as special if it immediately
follows "{}". My guess is that it was done this way to minimise the
chances of causing compatibility problems.
> I'm not saying that
> I oppose the entire idea; it's just that the SVR4 syntax is not
> compatible with POSIX, and that is a strike against it.
The SVR4 syntax is long-established existing practice that predates
POSIX.2, so its arguable that if it is not allowed by POSIX.2 then
that is an oversight in the standard - it should have explicitly
allowed the SVR4 behaviour as an extension. Standardizing the
behaviour would neatly solve the issue.
> I still favor the GNU extension of NUL termination instead. It's more
> reliable in the presence of multiple locales and encoding errors, and
NUL termination certainly has advantages over adding backslashes,
but I don't see any advantage over internal argument aggregation
by "find".
> it's easier to explain. Perhaps that's why it is documented and the
> Solaris behavior is not.
The SVR4 behaviour is documented in Unixware man pages, so it's odd
that it isn't documented by Solaris. Here is the description from a
Unixware 2.1 man page:
-exec cmd True if the executed cmd returns a zero value as
exit status. A command argument {} is replaced
by the current path name. The end of cmd must be
punctuated by an escaped semicolon or a plus sign
(+). When a plus sign is used, cmd aggregates a
set of pathnames and executes on the set; when a
semicolon is used, cmd executes on one pathname
at a time. The reason for preferring + to a
semicolon is vastly improved performance.
It shouldn't be too hard to update the XCUd5 description of "find"
based on this.
--
Geoff Clare yyy@xxxxxxxxxxx
UniSoft Limited, London, England. yyy@xxxxxxxxxx
|