Re: libpq environment variables in the server

Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:

> On 2019-03-15 05:00, Noah Misch wrote:
>> I consider the following style more idiomatic:
>>
>> {
>> local %ENV;
>> delete $ENV{PGAPPNAME};
>> ...
>> }
>
> That doesn't work because the first line clears the entire environment.

The solution to that is to do 'local %ENV = %ENV;', to assign a copy of
the original to the localised variable. This doesn't work on VMS,
because its concept of environment variables is quite different from
UNIX, but PostgreSQL doesn't support that anyway.

> What does work is
>
> {
> delete local $ENV{PGAPPNAME};
> ...
> }
>
> But that is documented as new in Perl 5.12.0, so we might not be able to
> use it. It appears to work in the 5.8.9 I have lying around, so I'm
> confused.

It "works" as in it's not a syntax error, but it doesn't actually
localise the deletion. The following program:

use strict;
use warnings;
use feature 'say';

our %env = qw(foo bar baz bat);
say "original: ", join(", ", sort keys %env);
{
delete local $env{foo};
say "localised: ", join(", ", sort keys %env);
}
say "restored? ", join(", ", sort keys %env);

on 5.12 prints:

original: baz, foo
localised: baz
restored? baz, foo

while on 5.10 it prints:

original: baz, foo
localised: baz
restored? baz

BTW, https://perl.bot/ is handy for testing things like this on various
Perl versions you don't have lying around.

- ilmari
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