reading_files.rb

require 'pry'
binding.pry

ruby reader.rb groucho harpo chico #Ruby load this file and pass in 3 arguments; 
ARGV #This is the argments array that you passed into the programme when you ran it; 

puts ARGV.join(', ')

if(ARGV[0] == 'groucho')
  puts "Hey there Groucho"
end

When you run rails server #Server is the argument 

touch brothers.txt 
ruby reader.rb brothers.txt
ARGV => ["brothers.txt"]
ARGF.each do {|line| puts line }

#Mention file names in ARGV then you are interate through the contents of the file with ARGF;