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Manual Reference Pages  -  MONITORING::PLUGIN::GETOPT (3)

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Monitoring::Plugin::Getopt - OO perl module providing standardised argument processing for Nagios plugins



  use Monitoring::Plugin::Getopt;

  # Instantiate object (usage is mandatory)
  $ng = Monitoring::Plugin::Getopt->new(
    usage => "Usage: %s -H <host> -w <warning> -c <critical>",
    version => 0.1,
    url =>,
    blurb => This plugin tests various stuff.,

  # Add argument - named parameters (spec and help are mandatory)
    spec => critical|c=i,
    help => q(Exit with CRITICAL status if fewer than INTEGER foobars are free),
    required => 1,
    default => 10,

  # Add argument - positional parameters - arg spec, help text,
  #   default value, required? (first two mandatory)
    q(Exit with WARNING status if fewer than INTEGER foobars are free),

  # Parse arguments and process standard ones (e.g. usage, help, version)

  # Access arguments using named accessors or or via the generic get()
  print $ng->opts->warning;
  print $ng->opts->get(critical);


Monitoring::Plugin::Getopt is an OO perl module providing standardised and simplified argument processing for Nagios plugins. It implements a number of standard arguments itself (--help, --version, --usage, --timeout, --verbose, and their short form counterparts), produces standardised nagios plugin help output, and allows additional arguments to be easily defined.


  # Instantiate object (usage is mandatory)
  $ng = Monitoring::Plugin::Getopt->new(
    usage => Usage: %s --hello,
    version => 0.01,

The Monitoring::Plugin::Getopt constructor accepts the following named arguments:
usage (required) Short usage message used with --usage/-? and with missing required arguments, and included in the longer --help output. Can include a ’%s’ sprintf placeholder which will be replaced with the plugin name e.g.

  usage => qq(Usage: %s -H <hostname> -p <ports> [-v]),

might be displayed as:

  $ ./check_tcp_range --usage
  Usage: check_tcp_range -H <hostname> -p <ports> [-v]

version (required) Plugin version number, included in the --version/-V output, and in the longer --help output. e.g.

  $ ./check_tcp_range --version
  check_tcp_range 0.2 []

url URL for info about this plugin, included in the --version/-V output, and in the longer --help output (see preceding ’version’ example).
blurb Short plugin description, included in the longer --help output (see below for an example).
license License text, included in the longer --help output (see below for an example). By default, this is set to the standard nagios plugins GPL license text:

  This nagios plugin is free software, and comes with ABSOLUTELY
  NO WARRANTY. It may be used, redistributed and/or modified under
  the terms of the GNU General Public Licence (see

Provide your own to replace this text in the help output.

extra Extra text to be appended at the end of the longer --help output.
plugin Plugin name. This defaults to the basename of your plugin, which is usually correct, but you can set it explicitly if not.
timeout Timeout period in seconds, overriding the standard timeout default (15 seconds).
The full --help output has the following form:

  version string

  license string


  usage string

  options list

  extra text

The ’blurb’ and ’extra text’ sections are omitted if not supplied. For example:

  $ ./check_tcp_range -h
  check_tcp_range 0.2 []

  This nagios plugin is free software, and comes with ABSOLUTELY NO WARRANTY.
  It may be used, redistributed and/or modified under the terms of the GNU
  General Public Licence (see

  This plugin tests arbitrary ranges/sets of tcp ports for a host.

  Usage: check_tcp_range -H <hostname> -p <ports> [-v]

   -h, --help
     Print detailed help screen
   -V, --version
     Print version information
   -H, --hostname=ADDRESS
     Host name or IP address
   -p, --ports=STRING
     Port numbers to check. Format: comma-separated, colons for ranges,
     no spaces e.g. 8700:8705,8710:8715,8760
   -t, --timeout=INTEGER
     Seconds before plugin times out (default: 15)
   -v, --verbose
     Show details for command-line debugging (can repeat up to 3 times)


You can define arguments for your plugin using the arg() method, which supports both named and positional arguments. In both cases the spec and help arguments are required, while the label, default, and required arguments are optional:

  # Define --hello argument (named parameters)
    spec => hello|h=s,
    help => "Hello string",
    required => 1,

  # Define --hello argument (positional parameters)
  #   Parameter order is spec, help, default, required?, label
  $ng->arg(hello|h=s, "Hello parameter (default %s)", 5, 1);

spec The spec argument (the first argument in the positional variant) is a Getopt::Long argument specification. See Getopt::Long for the details, but basically it is a series of one or more argument names for this argument (separated by ’|’), suffixed with an ’=<type>’ indicator if the argument takes a value. ’=s’ indicates a string argument; ’=i’ indicates an integer argument; appending an ’@’ indicates multiple such arguments are accepted; and so on. The following are some examples:
help The help argument is a string displayed in the --help option list output, or it can be a list (an arrayref) of such strings, for multi-line help (see below).

The help string is munged in two ways:
o First, if the help string does NOT begins with a ’-’ sign, it is prefixed by an expanded form of the spec argument. For instance, the following hello argument:

    spec => hello|h=s,
    help => "Hello string",

would be displayed in the help output as:

  -h, --hello=STRING
    Hello string

where the ’-h, --hello=STRING’ part is derived from the spec definition (by convention with short args first, then long, then label/type, if any).

o Second, if the string contains a ’%s’ it will be formatted via sprintf with the ’default’ as the argument i.e.

  sprintf($help, $default)

Multi-line help is useful in cases where an argument can be of different types and you want to make this explicit in your help output e.g.

    spec => warning|w=s,
    help => [
      Exit with WARNING status if less than BYTES bytes of disk are free,
      Exit with WARNING status if less than PERCENT of disk is free,
    label => [ BYTES, PERCENT% ],

would be displayed in the help output as:

 -w, --warning=BYTES
    Exit with WARNING status if less than BYTES bytes of disk are free
 -w, --warning=PERCENT%
    Exit with WARNING status if less than PERCENT of disk space is free

Note that in this case we’ve also specified explicit labels in another arrayref corresponding to the help one - if this had been omitted the types would have defaulted to ’STRING’, instead of ’BYTES’ and ’PERCENT%’.

label The label argument is a scalar or an arrayref (see ’Multi-line help’ description above) that overrides the standard type expansion when generating help text from the spec definition. By default, spec=i arguments are labelled as =INTEGER in the help text, and spec=s arguments are labelled as =STRING. By supplying your own label argument you can override these standard ’INTEGER’ and ’STRING’ designations.

For multi-line help, you can supply an ordered list (arrayref) of labels to match the list of help strings e.g.

  label => [ BYTES, PERCENT% ]

Any labels that are left as undef (or just omitted, if trailing) will just use the default ’INTEGER’ or ’STRING’ designations e.g.

  label => [ undef, PERCENT% ]

default The default argument is the default value to be given to this parameter if none is explicitly supplied.
required The required argument is a boolean used to indicate that this argument is mandatory (Monitoring::Plugin::Getopt will exit with your usage message and a ’Missing argument’ indicator if any required arguments are not supplied).
Note that --help lists your arguments in the order they are defined, so you should order your arg() calls accordingly.


The main parsing and processing functionality is provided by the getopts() method, which takes no arguments:

  # Parse and process arguments

This parses the command line arguments passed to your plugin using Getopt::Long and the builtin and provided argument specifications. Flags and argument values are recorded within the object, and can be accessed either using the generic get() accessor, or using named accessors corresponding to your argument names. For example:

  print $ng->get(hello);
  print $ng->hello();

  if ($ng->verbose) {
    # ...

  if ($ng->get(ports) =~ m/:/) {
    # ...

Note that where you have defined alternate argument names, the first is considered the citation form. All the builtin arguments are available using their long variant names.


The getopts() method also handles processing of the immediate builtin arguments, namely --usage, --version, --help, as well as checking all required arguments have been supplied, so you don’t have to handle those yourself. This means that your plugin will exit from the getopts() call in these cases - if you want to catch that you can run getopts() within an eval{}.

getopts() also sets up a default ALRM timeout handler so you can use an

  alarm $ng->timeout;

around any blocking operations within your plugin (which you are free to override if you want to use a custom timeout message).


Monitoring::Plugin, Getopt::Long


This code is maintained by the Monitoring Plugin Development Team: see

Gavin Carr <>


Copyright (C) 2014 by Monitoring Plugin Team Copyright (C) 2006-2014 by Nagios Plugin Development Team

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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perl v5.20.3 MONITORING::PLUGIN::GETOPT (3) 2015-04-11

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