use warnings;
use strict;
use Getopt::Long;

sub help  {
    print "Available options are: \n";
    print "\t--first\n";
    print "\t--help\n";
}

BEGIN{
	# no warnings; #strangely this is not able to suppress the warning "Undefined subroutine &main::first called at.."
	GetOptions(
	  'first' => \&first,
	  'help'     => \&help,
	) or &help and die "Invalid options passed to $0\n"
}

sub first  {
  print "Processing sub first\n";
}

__END__
perl getoptcheck.pl --year --first

Unknown option: year
Undefined subroutine &main::first called at ..perl5.26.64bit/perl/lib/Getopt/Long.pm line 606.
Available options are:
        --first
        --second
        --help
Invalid options passed to getoptcheck.pl
BEGIN failed--compilation aborted at getoptcheck.pl line 20.