Re: \dn [PATTERN] handling not quite right...

>> I haven't looked in great detail into why this is happpening, but it
>> seems as though processNamePattern() doesn't handle ?'s correctly in
>> the negative lookahead context correctly.
>
> Negative lookahead context!?  You are several sigmas beyond the subset
> of regex functionality that \d and friends are intended to support.
> Given that we're defining * and ? as shell-style wildcards, it's not
> going to be feasible to handle very much of ordinary regex usage let
> alone advanced.

I was worried you'd say as much.  I'm in a situation where I've got a
few hundred schemas floating around now and about half of them end with
_log or _shadow and I was surprised at how non-trivial it was to filter
out the _log or _shadow schemas with \dn.  I tried thinking up the psql
equiv of tcsh's fignore but had no luck (ex:  set fignore = (\~ .o
.bak)).

>> The more I think about this, a leading pipe could be used
>> to pipe the output to a utility, so that \dn | egrep -v '(log|shadow)
>> would work and would be the easiest solution.
>
> This on the other hand seems more like a potentially useful feature,
> although I'm unclear on what you expect to get sent through the pipe
> exactly --- you want column headers for instance?  What if you're using
> a nondefault display layout?

Instead of using printf(), fprintf(), fwrite(), or whatever it is that
psql(1) uses internally for displaying result sets, have it use the
following chunk of pseudo code:

if (pipe_symbol_found) {
    char buf[8192];
    size_t len = 0;
    memset(&buf, 0, sizeof(buf));

    fh = popen(..., "r+"); /* or setsocketpair() + fork() */
    fwrite(formatted_output_buffer, strlen(formatted_output_buffer), 1,
fh);

    while((len = read(fileno(fh), buf, sizeof(buf)))) {
        fwrite(buf, len, 1, stdout);
    }
} else {
    /* whatever the current code does */
}

That doesn't take into account the set option that lets you write the
output to a file, but that is trivial to handle.  To answer your
question, I'd send _everything_ through the pipe and use the pipe as a
blanket IO filter.  I haven't thought about this, but would it be
possible to hand the data off to sh(1) and have it handle the
pipe/redirection foo that way psql doesn't have to have any
pipe/redirection brains?  If so, I think that'd be slick since you
could do things like '\dn | tail -n +3 | grep -v blah' to handle your
concern about having the header sent through and a utility not wanting
it.

Too bad tee(1) doesn't support a -p option to have tee(1)'s argument
sent to sh(1) or a pipe instead of a file, then there'd be some real
interesting things that one could script.  Ex:

    \dn | tee -p 'head -n 3 >> /dev/stdout' | tail -n +3 | egrep -v
'_(log|shadow)$'

Which'd show you the header, but everything after the header would be
sent to egrep(1). I can't understand why win32 users think *NIX's CLI
can be confusing.... *grin*.

Just some thoughts.  -sc

--
Sean Chittenden