gem install ruby-nmap ronin-scanners gems
As far as you understand how to use nmap and how basically it works, you'll find this lib is easy to use. You can do most of nmap functionality

Basic Scan

Ruby-nmap gem is a Ruby interface to nmap, the exploration tool and security / port scanner.
  • Provides a Ruby interface for running nmap.
  • Provides a Parser for enumerating nmap XML scan files.
let's see how it dose work.
require 'nmap'
scan = Nmap::Program.scan(:targets => '', :verbose => true)

SYN Scan

require 'nmap/program'
Nmap::Program.scan do |nmap|
nmap.syn_scan = true
nmap.service_scan = true
nmap.os_fingerprint = true
nmap.xml = 'scan.xml'
nmap.verbose = true
nmap.ports = [20,21,22,23,25,80,110,443,512,522,8080,1080,4444,3389]
nmap.targets = '192.168.1.*'
each option like nmap.syn_scan or nmap.xml is considered as a Task. Documentation shows the list of scan tasks/options that are supported by the lib.

Comprehensive scan

#!/usr/bin/env ruby
require 'nmap/program'
Nmap::Program.scan do |nmap|
# Target
nmap.targets = ''
# Verbosity and Debugging
nmap.verbose = true
nmap.show_reason = true
# Port Scanning Techniques:
nmap.syn_scan = true # You can use nmap.all like -A in nmap
# Service/Version Detection:
nmap.service_scan = true
nmap.os_fingerprint = true
nmap.version_all = true
# Script scanning
nmap.script = "all"
nmap.all_ports # nmap.ports = (0..65535).to_a
# Firewall/IDS Evasion and Spoofing:
nmap.decoys = ["google.com","yahoo.com","hotmail.com","facebook.com"]
nmap.spoof_mac = "00:11:22:33:44:55"
# Timing and Performance
nmap.min_parallelism = 30
nmap.max_parallelism = 130
# Scan outputs
nmap.output_all = 'rubyfu_scan'

Parsing nmap XML scan file

I made an aggressive scan on scanme.nmap.org
nmap -n -v -A scanme.nmap.org -oX scanme.nmap.org.xml
I quoted the code from official documentation (https://github.com/sophsec/ruby-nmap)
require 'nmap/xml'
Nmap::XML.new(ARGV[0]) do |xml|
xml.each_host do |host|
puts "[#{host.ip}]"
# Print: Port/Protocol port_status service_name
host.each_port do |port|
puts " #{port.number}/#{port.protocol}\t#{port.state}\t#{port.service}"
22/tcp open ssh
80/tcp open http
9929/tcp open nping-echo