On Fri, Aug 17, 2012 at 02:01:25PM -0400, Bruce Momjian wrote:
> On Fri, Aug 17, 2012 at 06:55:14PM +0100, Richard Huxton wrote:
> > >Well, it'd be nice to allow substitution there ...
> > >
> > >>What we can't easily do is to allow quotes to prevent variable
> > >>substitution in these whole-line commands because we can't process the
> > >>quotes because that will remove them.
> > >
> > >... but if there is then no way to prevent it, that's absolutely
> > >unacceptable.
> >
> > If I'm understanding this correctly, \copy parsing just passes the
> > query part unaltered as part of a COPY statement back into the
> > top-level parser. Likewise with the \!shell stuff (but presumably to
> > execve).
> >
> > To handle variable-substitution correctly for \copy we'd need to
> > duplicate the full parsing for COPY. For \! we'd need something
> > which understood shell-syntax (for the various shells out there).
> > Ick.
> >
> > Or you'd need a separate variable-bracketing {{:x}} syntax that
> > could work like reverse dollar-quoting. Also Ick.
> >
> > As far as we know this has only inconvenienced one person (me) badly
> > enough to report a maybe-bug. Thanks for trying Bruce, but I fear
> > this is one itch that'll go unscratched.
> >
> > Rest assured I'm not about to storm off and replace all my
> > installations with MySQL :-)
>
> Good analysis. Basically we can't hope to fully understand COPY or
> shell quoting syntax well enough to properly replace only unquoted psql
> variable references.
>
> Therefore, unless I hear otherwise, I will just document the limitation
> and withdraw the patch.
Patch withdrawn. Seems documentation was already in place --- I
clarified \! limitations match \copy.
-- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB
http://enterprisedb.com
+ It's impossible for everything to be true. +