From: Dave Thacker <dthacker@...>
Date: 2007-12-23T04:13:20+09:00
Subject: Diagnosing error in command line input

I'm working on a program (my first) that will need to read user input (a file 
name) from the command line.  While looking for examples of reading command 
line input, I stumbled across this example(1) which I've cut and pasted, to 
see how it works.  
#!/usr/bin/ruby
require 'readline'

def prompt(prompt="> ")
  input = nil
  prompt += " " unless prompt =~ /\s$/
  loop do
    input = Readline.readline(prompt, true)
    break if input.length > 0
  end
  return input
end

apples = prompt("how many apples do you have?")
pears = prompt("how many pears do you have?")
nonsense = prompt("try my input history (up/down arrow)")

printf "there are %d items in our input history\n",
       Readline::HISTORY

When I run this I get:
dthacker@buckbeak:~/learning/ruby$ ./test-cl-io.rb
how many apples do you have? 3
how many pears do you have? 7
try my input history (up/down arrow) 5
./test-cl-io.rb:18:in `printf': can't convert Object into Integer (TypeError)
        from ./test-cl-io.rb:18

I'm guessing that HISTORY is not the method I want to call.  Is that my 
problem?  Or is there a simple newbie syntax error I'm making?  
TIA   
Dave

(1)http://beaver.net/slides/ruby/10-easy-pieces.html