How can I fix `"main::HKEY_LOCAL_MACHINE" used only once` warnings when using Perl's Win32::Registry? - perl

Question

I have a script that would get a registry key value. Here's the code.
use strict;
use warnings;
my $winRegistryStatus=0;
eval {
require Win32::Registry;
Win32::Registry->import();
};
unless($#) {
$winRegistryStatus=1;
}
my $registryPath = "Self\Random";
my $keyName = "Configure";
my $registryKeySettings;
my %registrySubKeyValues;
$main::HKEY_LOCAL_MACHINE->Open($registryPath, $registryKeySettings) || die "Cannot open $registryPath: $!";
$registryKeySettings->GetValues(\%registrySubKeyValues); # get sub keys and value -hash ref
foreach my $subKey (keys %registrySubKeyValues) {
my $_subKey = $registrySubKeyValues{$subKey};
next unless $$_subKey[0] eq $keyName;
print "Configure=" . $$_subKey[2];
}
Output
Name "main::HKEY_LOCAL_MACHINE" used only once: possible typo at ....
Configure=Yes
I could get the value of Configure but it also returns a warning which I don't know how to fix it.
Any body where am I wrong and could show me how to fix it?
Thanks.

Answer 1

The "used only once" is a warning that use warnings issues because you have used $main::HKEY_LOCAL_MACHINE only once. You are not at fault here. It is a mere hint that you might have forgotten something.
In this case, you can either ignore it, or simply deactivate that kind of warning: no warnings 'once'.
In general it is a good idea to enclose these things in a BLOCK and add a long, descriptive comment to it that explains why you are turning off that kind of warning here.
{ # Disable 'used only once' warning because the $::HKEY_...
# var was imported by Win32::Registry and is not used anywhere else.
$main::HKEY_LOCAL_MACHINE->Open($registryPath, $registryKeySettings)
|| die "Cannot open $registryPath: $!";
}
You can find more infos about warnings here.

Answer 2

This module is rather odd in that it exports symbols to the main package regardless of where it is used from.
But in your case this is what you want: your program is in main as you have no package statement, and you can omit the main:: from $HKEY_LOCAL_MACHINE.
As to your problem, the code you show doesn't raise the warning you say it does. The problem must be somewhere else. Please would you show your full code so that we can advise you better.
In the mean time please pay heed to #Sinan Ünür's advice - Win32::TieRegistry is preferable to Win32::Registry. Even the POD documentation of Win32::Registry says this:
NOTE: This module provides a very klunky interface to access the
Windows registry, and is not currently being developed actively. It
only exists for backward compatibility with old code that uses it. For
more powerful and flexible ways to access the registry, use
Win32::TieRegistry.
Update
I understand the problem having seen the update to your question and it is because you are executing the require Win32::Registry at run time. That means that $HKEY_LOCAL_MACHINE doesn't exist at compile time and so the compiler complains about it.
The fix is to declare it at compile time with
our $HKEY_LOCAL_MACHINE
at the top of the program.
By the way there is no need for the import call if all you need is this scalar.