slapd_ munin插件中串聯（。）或字符串中未初始化值的使用

Question

我正在嘗試使用perl編寫的slapd_ munin插件，我幾乎不知道該插件。 The full plugin is available here。我得到的錯誤是這一個：

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

232線路是這一個：

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

我通過outputing所有變量試圖調試/對象如下：

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

當我再次運行它時，我得到：

[...] # 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. 

由於所有的變量似乎設置，我真的不明白我得到的錯誤信息

問：任何人都可以建議如何調試此腳本？

Answer 1

您應該轉儲參考到%ops，如

print Dumper \%ops; 

這將使調試輸出更清晰。爲了說明這一點，考慮

#! /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); 

通知的輸出如何在下半年更清楚地看到結構：

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

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

你切出的輸出的關鍵位。 $VAR15的價值是多少？是"localhost"還是別的？

當您打印$searchdn時，它的價值是多少？