Use of uninitialized value in concatenation (.) or string in slapd_ munin plugin - perl

Question

I'm trying to implement the slapd_ munin plugin which is written in perl which I'm pretty much clueless about. The full plugin is available here. The error I'm getting is this one:
Use of uninitialized value in concatenation (.) or string at
/etc/munin/plugins/slapd_localhost line 232, <DATA> line 275.
Line 232 is this one:
my $searchdn = $ops{$action}->{'search'} . "," . $basedn;
I tried debugging by outputing all the variables/objects as follows:
use Data::Dumper; # top of script
# [...]
print Dumper(%ops);
print "action = [$action]\n";
print "basedn = [$basedn]\n\n";
my $searchdn = $ops{$action}->{'search'} . "," . $basedn;
When I run it again here is what I obtain:
[...] # 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.
Since all the variables seem to be set, I really don't understand the error message I'm getting
Q: Can anybody advise on how debugging this script?

Answer 1

You should dump a reference to %ops, as in
print Dumper \%ops;
This will make the debug output clearer. To illustrate, consider the output of
#! /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);
Notice how you see the structure much more clearly in the latter half:
No reference:
$VAR1 = 'baz';
$VAR2 = {
'quux' => 3
};
$VAR3 = 'foo';
$VAR4 = {
'bar' => 1
};
Reference:
$VAR1 = {
'baz' => {
'quux' => 3
},
'foo' => {
'bar' => 1
}
};
You cut out a critical bit of the output. What's the value of $VAR15? Is it "localhost" or something else?
When you print $searchdn, what is its value?