ip_route_match.rb

#!/usr/bin/env ruby -wKU

def ip_route_match(command, regex)
  command.split("\n").select { |l| l =~ regex }.first.to_s[/([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)/] || '0.0.0.0'
end

c = '10.128.0.0/24 dev eth1  proto kernel  scope link  src 10.128.0.48
127.0.0.0/8 dev lo  scope link
default via 10.128.0.254 dev eth1'
# c = %x{/sbin/ip route list match #{ip}}
p ip_route_match(c, /^default via /) # => '10.128.0.254'
p ip_route_match(c, /via /) # => '10.128.0.254'
p ip_route_match(c, /^default crap /) # => '0.0.0.0'