在 slapd_ munin 插件中的串联 (.) 或字符串中使用未初始化的值

Question

我正在尝试实现 slapd_ munin 插件，该插件是用 perl 编写的，但我对此一无所知。 完整的插件位于此处。我得到的错误是这个：

Use of uninitialized value in concatenation (.) or string at
/etc/munin/plugins/slapd_localhost line 232, <DATA> line 275.

第 232 行是这个：

 my $searchdn = $ops{$action}->{'search'} . "," . $basedn;

我尝试通过输出所有变量/对象进行调试，如下所示：

use Data::Dumper;   # top of script
# [...]
print Dumper(%ops);
print "action = [$action]\n";
print "basedn = [$basedn]\n\n";
my $searchdn = $ops{$action}->{'search'} . "," . $basedn;

当我再次运行它时，这是我得到的：

[...] # 15 other variables belonging to $ops
$VAR16 = {
           'info' => 'The graph shows the number of Waiters',
           'search' => 'cn=Waiters',
           'desc' => 'The current number of Waiters',
           'filter' => '(|(cn=Write)(cn=Read))',
           'title' => 'Number of Waiters',
           'label2' => {
                         'read' => 'Read',
                         'write' => 'Write'
                       },
           'vlabel' => 'Waiters'
         };
action = [localhost]
action = [cn=Monitor]

Use of uninitialized value in concatenation (.) or string at /etc/munin/plugins/slapd_localhost line 237, <DATA> line 275.

由于所有变量似乎都已设置，所以我我真的不明白我收到的错误消息

问：任何人都可以建议如何调试此脚本吗？

Answer 1

您应该将引用转储到%ops，如

print Dumper \%ops;

这将使调试输出更清晰。为了说明这一点，请考虑以下输出：

#! /usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my %h = (foo => { bar => 1 }, baz => { quux => 3 });

print "No reference:\n",
      Dumper(%h),
      "\n",
      "Reference:\n",
      Dumper(\%h);

注意您如何在后半部分更清楚地看到结构：

No reference:
$VAR1 = 'baz';
$VAR2 = {
          'quux' => 3
        };
$VAR3 = 'foo';
$VAR4 = {
          'bar' => 1
        };

Reference:
$VAR1 = {
          'baz' => {
                     'quux' => 3
                   },
          'foo' => {
                     'bar' => 1
                   }
        };

您删除了输出的关键位。 $VAR15 的值是多少？是 "localhost" 还是其他？

当你打印 $searchdn 时，它的值是多少？