Re: psql --help=variables lists variables that can't be set

On 2015-12-03 22:08:31 -0500, Peter Eisentraut wrote:
> psql --help=variables shows variables treated specially by psql. And it
> tells you
>
> Usage:
> psql --set=NAME=VALUE
> or \set NAME VALUE
>
> But some of the variables listed cannot usefully be set, only read, such as
>
> DBNAME the currently connected database name
> HOST the currently connected database server
> LASTOID the value of last affected OID
>
> These can be read in a script, but there is nothing useful you can do
> with them on the command line.

Well, you can display them, which actually isn't uninteresting (-c
'\echo :DBNAME'), and at least LASTOID is rather interesting for
scripting purposes.

> Also, for variables such as HISTCONTROL, IGNOREEOF, PROMPT*, they are
> more commonly set in psqlrc, not on the command line.
>
> Should we trim this list down to variables that are actually useful to
> set on the command line?

I think the increased discoverability isn't a bad thing, so I'm inclined
to not do that.

> I also have some concerns about the listed environment variables. The
> list of libpq PG* variables is incomplete, and if we're going to curate
> the list, we surely don't need to show the "not recommended" PGPASSWORD
> variable.
>
> That list probably also needs some ifdefs, since SHELL and TMPDIR don't
> work on Windows, and PSQL_HISTORY only works when readline support is built.

I don't have much an opinion about those. I think it's not too bad to
show them regardless, nor is it bad to hide them.