New to ruby - need assistance with rewriting a script

Hello,

I'm working on learning ruby and trying to figure out how I would take
an existing example and rewrite it in a way that suits my own usage.
What I'm looking for here isn't for someone to just give me a block of
fixed code and be like, "Oh, here you go!" since I won't actually learn
anything from that.

So, here's the script:

####
require 'rubygems'
require 'crontab-parser'

start_time = Time.parse(ARGV[0])
end_time   = Time.parse(ARGV[1])

them
cron_data = File.readlines(ARGV[2]).select {|line| line =~ /^[0-9*]/}
cron  = CrontabParser.new(cron_data.join("\n"))
(start_time..end_time).each do |timestamp|
  next unless timestamp.sec.to_i == 0
  cron.each do |cron_entry|
    if cron_entry.should_run?(timestamp)
      puts "#{timestamp}\t#{cron_entry.cmd}"
    end
  end
end
####

Again, not my code. What I want to do is like so:

1. Run this script without requiring any CLI arguments. I know the time
interval I want to search for (between 1 and 14 minutes) but I don't
want to have to type out the range of times when I execute the script.
I've seen the chronic gem and believe this is the answer I'm looking
for, but not certain of how I'd integrate that in here.

2. Scan all of the files in a directory with the exception of two (of
which I'd need to set an .excludes). Something like this (my code):

####
Dir["/var/spool/cron/*"].each do |file|
  username = file.split("/").last
  crontab = CrontabParser.new(File.read(file))

  crontab.each do |cron|
    puts "User: #{username}"
    # Do whatever
  end
end
####

This way I can get the output of:

User1
cron1
cron2

User2
Cron1
Cron2

And so on.

Can anyone offer some sort of assistance in helping me get this to where
I want it? I'm happy with any kind of relevant documentation for this
task (there's so much unrelated documentation that I end up
lost/confused), examples that are similar in what I'm trying to do, or
partial
answers that will point me in the right direction.

I know this may seem a bit unorthodox, but it's how I learn - I can't
just read a book on ruby and understand how to do everything (I've read
Chis Pine's book and it has helped a little, but not enough for me to be
able to do something like this on my own).

Thanks in advance!

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