A simple Nagios plugin that makes an HTTP request and interprets a JSON response; implemented in Ruby - because why not? This is really more of a proof of concept than something super useful, so ymmv. ;)

simple-nagios-json.rb

#!/usr/bin/ruby1.9.1

# Nagios plugin that looks for some JSON or summat.

require 'json'
require 'net/http'
require 'uri'
require 'optparse'

@options = {}

# display verbose output (if being run by a human for example)
def say msg
    if @options[:verbose] == true
        puts msg
    end
end

def do_exit code
    if @options[:verbose] == true
        exit 3
    else
        exit code
    end
end

# Parse cli args
optparse = OptionParser.new do |opts|
    opts.banner = 'Usage: %s [-V] -u <URI> -n <name> -v <value>' % [$0]

    opts.on('-h', '--help', 'Help info') do
        puts opts
        do_exit(3)
    end

    @options[:uri] = nil
    opts.on('-u', '--uri URI', 'Target URI') do |uri|
        @options[:uri] = uri
    end

    @options[:name] = nil
    opts.on('-n', '--name NAME', 'Name of the variable') do |name|
        @options[:name] = name
    end

    @options[:value] = nil
    opts.on('-v', '--value VALUE', 'Value of the variable') do |value|
        @options[:value] = value
    end

    @options[:verbose] = false
    opts.on('-V', '--verbose', 'Human output') do
        @options[:verbose] = true
    end
end

# Get those args!
optparse.parse!

error_msg = []

if not @options[:uri] then
    error_msg.push('Need to specify the URI.')
end
if not @options[:name] then
    error_msg.push('Need to specify the name of the variable.')
end
if not @options[:value] then
    error_msg.push('Need to specify a value for the variable.')
end

if error_msg.count > 0 then
    puts 'Aborting for the following reason(s):'
    error_msg.each do |msg|
        puts msg
    end
    puts "$ %s --help   for more information." % [$0]
    do_exit(3)
end

uri = URI.parse(@options[:uri])

http = Net::HTTP.new(uri.host, uri.port)
request = Net::HTTP::Get.new(uri.request_uri)

response = http.request(request)

# We must get a proper response
if not response.code.to_i == 200 then
    puts 'CRIT: Received HTTP code %s instead of 200.' % [response.code]
    do_exit(2)
end

say("---\nRESPONSE: %s\n---" % [response.body])

json = JSON.parse response.body

json.each do |name,value|
    if name == @options[:name] then
        if value.to_s == @options[:value].to_s then
            puts 'OK: %s => %s' % [name, value]
            do_exit(0)
        else
            puts 'CRIT: %s => %s' % [name, value]
            do_exit(2)
        end
    end
end