An example of OptionParser

opt_parser.rb

#!/usr/bin/env ruby

require 'optparse'


class LogParser
  def self.parse(log_file, index)
    data = []

    File.open(log_file).each do |line|
      t = line.split(' ')[index]
      data.push(t) if t
    end

    data.sort
  end

  def initialize(log_file, index)
    @times = []
    @times = LogParser.parse(log_file, index)

    self
  end

  def percentile(p)
    (@times.size * p / 100) - 0.5
  end
end


class Cli
  def self.run(arguments)
    options = {}

    OptionParser.new do |o|
      o.on("-fFILE", "--logfile=FILE", "Log file") { |f| options[:log_file] = f }
      o.on("-iINDEX", "--index=INDEX", "Index of the field") { |i| options[:index] = i.to_i }
    end.parse!

    puts LogParser.new(options[:log_file], options[:index]).percentile(70) if options[:log_file] && options[:index]
  rescue Exception => e
    $stderr.puts e.message
  end
end

# ::main::
Cli.run(ARGV) if __FILE__ == $0