HowToWritePlugins > Perl plugins

Perl Plugins

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Using Munin::Plugin module

You shall put these lines before using Munin::Plugin functions :

  use lib $ENV{'MUNIN_LIBDIR'};
  use Munin::Plugin;

If your Munin installation predates the MUNIN_* environment variables (introduced in 1.3.3) you can put this in your plugin configuration:

      env.MUNIN_PLUGSTATE /var/lib/munin-node/plugin-state
      env.MUNIN_LIBDIR /usr/share/munin

The module exports these functions: clean_fieldname, set_state_name, save_state, restore_state, tail_open, tail_close.

Avoid hacks

There are many perl plugins with constructs like the following to get environment values :

$var = $ENV{var} || somevalue;

This is wrong and may led to unexpected results.

The right way to write this is one of the following, depending on how you interpret environment values :

$var = exists $ENV{var}  ? $ENV{var} : somevalue;
$var = defined $ENV{var} ? $ENV{var} : somevalue;

To understand why, run the following script :

#! /usr/bin/perl -w
my %X = (a => 0, b => 2, c => "", d => undef);
foreach my $i (qw(a b c d e)) {
  my $y = $X{$i} || "ok";
  printf "%s  %s\n", $i, $y;

and you'll see that the only correct results are for b and e.

The reason is that || is a boolean operator over two boolean values and nor $X{$i} nor "ok" are boolean values.

Last modified at 2018-03-13T21:52:12+01:00 Last modified on 2018-03-13T21:52:12+01:00