rnagios
Ruby gem to make creating Nagios plugins easier
There are two types of checks you can perform that Nagios will process: active and NSCA checks. Active checks are run on the Nagios monitoring host and actively check services. NSCA checks are run by remote hosts and their output is sent back to the host for processing by the NSCA daemon. Active checks are "actively" run by Nagios; NSCA checks are "passively" run by other servers.
To create an active check, create logic that measures a service (such as a database, a web service, or a custom application) and returns a fully-populated ActiveStatus object. By the same token, to create an NSCA check, create logic that measures a service and returns a fully-populated NscaHostStatus or NscaServiceStatus object. (There are many gems available that can help you connect to services and parse their output; this class does not attempt to be everything to everyone.)
RNagios handles the formatting, and provides the appropriate exit code so Nagios will process it correctly. When running on UNIX/Linux, Nagios will check the exit codes along with the string in the status message to determine how to handle it. Under Windows, Nagios only cares about the strings in the status message.
RNagios allows you to use an optional configuration file in case your plugin requires access to multiple configuration parameters. If you supply a configuration file, it should be a YAML file, and it will be parsed in the check method before the measure method is called. measure() can then use the @config attribute to access configuration parameters. The configuration file is expected to be in the same directory as the plugin.