如何在perl中正确使用全局变量

概述我是perl的新手.我试图通过编写一些程序来理解它.在perl中确定范围让我很难过. 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="r 我是perl的新手.我试图通过编写一些程序来理解它.在perl中确定范围让我很难过.

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,我们会将这些声明为主代码和子程序的全局变量.但是,这给出了以下输出：

#~/perlscripts/dbtest.pl -c hellosUse 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 isUse 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 isDBI 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,而宁愿将它们用作全局变量.有人可以帮我确定我对范围界定的误解吗？

解决方法 调用子例程时,不会声明变量：

&ArgParser;                 # subroutine callour ($sqluser,$sqlpass);    # declaration$sqluser="root";            # assignment$sqlpass="mypassword";

为了在子例程中使用这些全局变量,将子例程放在变量声明之后.

但是,使用全局变量是一件坏事,您应该尽可能避免使用它.你可以这样做,例如：

my $sqluser = "root";my $sqlpass = "mypass";ArgParser($sqluser,$sqlpass);    # you should not use & in subroutine calls

然后在子程序内：

sub ArgParser {    my ($sqluser,$sqlpass) = @_;    ...

这样,您的变量就可以很好地封装,并且不会被意外 *** 作.

关于&符号&在子程序调用中,这在perldoc perlsub中记录：

To call subroutines:name(List);   # & is optional with parentheses.name List;    # Parentheses optional if predeclared/imported.&name(List);  # Circumvent prototypes.&name;        # Makes current @_ visible to called subroutine.

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