On 17/08/12 18:38, Tom Lane wrote:
Bruce Momjian<br...@momjian.us>  writes:
On Fri, Oct 21, 2011 at 05:31:41PM -0400, Robert Haas wrote:
I'm not sure whether that's a bug per se, but I can see where a
behavior change might be an improvement.

I did some research on this and learned a little more about flex rules.

Turns out we can allow variable substitution in psql whole-line
commands, like \copy and \!, by sharing the variable expansion flex
rules with the code that does argument processing.

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

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 :-)

  Richard Huxton
  Archonet Ltd

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