From: ilmari@ilmari.org
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Noah Misch <noah@leadboat.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: libpq environment variables in the server
Date: Fri, 15 Mar 2019 10:06:29 +0000
Message-ID: <d8j4l845u56.fsf@dalvik.ping.uio.no> (raw)
In-Reply-To: <872a3a54-a169-acfc-322a-f6c5b8e89ece@2ndquadrant.com>
References: <33383613-690e-6f1b-d5ba-4957ff40f6ce@2ndquadrant.com>
<744962da-c27f-c992-4058-364463857ee0@2ndquadrant.com>
<20190303080620.GA1750246@rfd.leadboat.com>
<35af0500-5eea-d2f0-339e-07a457a5f6bc@2ndquadrant.com>
<20190315040053.GB2607362@rfd.leadboat.com>
<872a3a54-a169-acfc-322a-f6c5b8e89ece@2ndquadrant.com>
Peter Eisentraut <peter.eisentraut@2ndquadrant.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
--
- Twitter seems more influential [than blogs] in the 'gets reported in
the mainstream press' sense at least. - Matt McLeod
- That'd be because the content of a tweet is easier to condense down
to a mainstream media article. - Calle Dybedahl
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To: pgsql-hackers@postgresql.org
Cc: ilmari@ilmari.org, peter.eisentraut@2ndquadrant.com, noah@leadboat.com
Subject: Re: libpq environment variables in the server
In-Reply-To: <d8j4l845u56.fsf@dalvik.ping.uio.no>
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