如何在Perl中正确使用全局变量(How to properly use Global variables in perl)

 我是perl的新手。 我试图通过编写一些程序来理解它。 perl中的范围界定让我很难。 
 
 我写了以下内容： 
 
use 5.16.3;
use strict;
use Getopt::Long;

Getopt::Long::Configure(qw(bundling no_getopt_compat));
&ArgParser;
our ($sqluser,$sqlpass);

$sqluser="root";
$sqlpass="mypassword";

sub ArgParser {
    print "Username is ".$sqluser." Password is ".$sqlpass."\n";
    my $crt='';
    my $delete='';
    GetOptions ('create|c=s' => \$crt,
        'delete|d=s' => \$delete
    );
    if ($crt) {
        &DatabaseExec("create",$crt);   
    } elsif ($delete) {
        &DatabaseExec("delete",$delete);    
    } else {
    print "No options chosen\n";
    }
}

sub DatabaseExec {
    use DBI;
    my $dbname=$_[1];
    print "Username is ".$sqluser." Password is ".$sqlpass."\n";
    my $dbh = DBI->connect("dbi:mysql:", $sqluser,$sqlpass);
    my $comand=$_[0];
    if ($_[0] eq "create") {
        my $db_com="create database ".$dbname;
        print 1 == $dbh->do($db_com) ? "Database created\n":"An error occured while creating database. Maybe it exists?\n";
        #print "Executing: ".$db_com."\n";
    } elsif ($_[0] eq "delete") {
        my $db_com="DROP DATABASE ".$dbname;
        #print "Executing: ".$db_com."\n";
        print 1 == $dbh->do($db_com) ? "Database deleted\n":"An error occured while creating database. Maybe it exists?\n";
    }
}
 
 我的理解是，我们会将这些声明声明为使用主代码和子例程的全局变量。 但是，这给出了以下输出： 
 
#~/perlscripts/dbtest.pl -c hellos
Use of uninitialized value $sqluser in concatenation (.) or string at /root/perlscripts/dbtest.pl line 20.
Use of uninitialized value $sqlpass in concatenation (.) or string at /root/perlscripts/dbtest.pl line 20.
Username is  Password is
Use of uninitialized value $sqluser in concatenation (.) or string at /root/perlscripts/dbtest.pl line 44.
Use of uninitialized value $sqlpass in concatenation (.) or string at /root/perlscripts/dbtest.pl line 44.
Username is  Password is
DBI connect('','',...) failed: Access denied for user 'root'@'localhost' (using password: NO) at /root/perlscripts/dbtest.pl line 45.
Can't call method "do" on an undefined value at /root/perlscripts/dbtest.pl line 50.
 
 我不想将这些作为参数传递给sub，而是将它们用作全局变量。 有人能帮助我确定我对范围的误解吗？ 

I am a novice to perl. I'm trying to understand it by writing some programs. Scoping in perl is giving me a hard time.
 
I wrote the following:
 
use 5.16.3;
use strict;
use Getopt::Long;

Getopt::Long::Configure(qw(bundling no_getopt_compat));
&ArgParser;
our ($sqluser,$sqlpass);

$sqluser="root";
$sqlpass="mypassword";

sub ArgParser {
    print "Username is ".$sqluser." Password is ".$sqlpass."\n";
    my $crt='';
    my $delete='';
    GetOptions ('create|c=s' => \$crt,
        'delete|d=s' => \$delete
    );
    if ($crt) {
        &DatabaseExec("create",$crt);   
    } elsif ($delete) {
        &DatabaseExec("delete",$delete);    
    } else {
    print "No options chosen\n";
    }
}

sub DatabaseExec {
    use DBI;
    my $dbname=$_[1];
    print "Username is ".$sqluser." Password is ".$sqlpass."\n";
    my $dbh = DBI->connect("dbi:mysql:", $sqluser,$sqlpass);
    my $comand=$_[0];
    if ($_[0] eq "create") {
        my $db_com="create database ".$dbname;
        print 1 == $dbh->do($db_com) ? "Database created\n":"An error occured while creating database. Maybe it exists?\n";
        #print "Executing: ".$db_com."\n";
    } elsif ($_[0] eq "delete") {
        my $db_com="DROP DATABASE ".$dbname;
        #print "Executing: ".$db_com."\n";
        print 1 == $dbh->do($db_com) ? "Database deleted\n":"An error occured while creating database. Maybe it exists?\n";
    }
}
 
It was my understanding that our would declare these as global variables for the use of the main code, and subroutines. However this gives the following output:
 
#~/perlscripts/dbtest.pl -c hellos
Use of uninitialized value $sqluser in concatenation (.) or string at /root/perlscripts/dbtest.pl line 20.
Use of uninitialized value $sqlpass in concatenation (.) or string at /root/perlscripts/dbtest.pl line 20.
Username is  Password is
Use of uninitialized value $sqluser in concatenation (.) or string at /root/perlscripts/dbtest.pl line 44.
Use of uninitialized value $sqlpass in concatenation (.) or string at /root/perlscripts/dbtest.pl line 44.
Username is  Password is
DBI connect('','',...) failed: Access denied for user 'root'@'localhost' (using password: NO) at /root/perlscripts/dbtest.pl line 45.
Can't call method "do" on an undefined value at /root/perlscripts/dbtest.pl line 50.
 
I would not like to pass these as arguments to the sub, and would rather use them as global variables. Could someone help me determine my misunderstanding of scoping?

原文：https://stackoverflow.com/questions/16035441