Resolve IPs for a CSV with hosts on the last column

resolve_csv_hosts.rb

#! /bin/env ruby
require 'socket'

if ARGV.length != 1
  puts "# Usage: #{$0} FILNAME.csv"
  exit(-1)
end

input_filename = ARGV.first
unless File.exist? input_filename
  puts "# File: #{filename} does not exist."
  puts "# Usage: #{$0} FILNAME.csv"
  exit(-1)  
end

first_timestamp = nil
File.readlines(input_filename).each do |line|
  split_line = line.split(',')
  if split_line.length == 3 && split_line.last != nil
    first_timestamp = split_line.first unless first_timestamp
    hostname = split_line.last.chomp
    begin      
      ip_address = IPSocket.getaddress(hostname)
      split_line[2] = ip_address
      split_line[0] = split_line[0].to_f - first_timestamp.to_f
      puts split_line.join(',')
    rescue Exception => e      
      puts "Error resolving: #{hostname}: #{e}"
    end
  else
    puts "Skipping invalid line: #{line}"
  end
end