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From: Hd Pwnz0r on 31 Jul 2010 17:46
Hi.

I'm learning Ruby and I want to know how to make a script have an
argument, i.e.

ruby script.rb 3 2

So far I have this:

abort "Correct syntax is ruby [script].rb [number to exponentially
multiply by] [exponent]" unless ARGV.size == 2
var = gets.chomp
var2 = gets.chomp
puts (var.to_i ** var2)

It's a simple exponential calculator.

I get this error when trying to run it with 2 arguments (2 and 3).

exponent.rb:2:in `gets': No such file or directory - 2 (Errno::ENOENT)
from exponent.rb:2:in `gets' from exponent.rb:2:in `<main>'

Attachments:
http://www.ruby-forum.com/attachment/4895/exponent.rb

--
Posted via http://www.ruby-forum.com/.

From: Jesús Gabriel y Galán on 31 Jul 2010 19:13
On Sat, Jul 31, 2010 at 11:46 PM, Hd Pwnz0r
<human.dictionary(a)rocketmail.com> wrote:
> Hi.
>
> I'm learning Ruby and I want to know how to make a script have an
> argument, i.e.
>
> ruby script.rb 3 2
>
> So far I have this:
>
> abort "Correct syntax is ruby [script].rb [number to exponentially
> multiply by] [exponent]" unless ARGV.size == 2
> var = gets.chomp
> var2 = gets.chomp

You have the program arguments in the ARGV array, as you probably
know, since you've used it in the previous line:

var = ARGV[0].to_i
var2 = ARGV[1].to_i

(I've added the to_i, since it seems you want to use them as numbers)

> puts  (var.to_i ** var2)
>
> It's a simple exponential calculator.
>
> I get this error when trying to run it with 2 arguments (2 and 3).
>
> exponent.rb:2:in `gets': No such file or directory - 2 (Errno::ENOENT)
> from exponent.rb:2:in `gets'        from exponent.rb:2:in `<main>'

Jesus.

From: James Harrison on 1 Aug 2010 02:16

On Jul 31, 2010, at 3:46 PM 7/31/10, Hd Pwnz0r wrote:

> Hi.
>
> I'm learning Ruby and I want to know how to make a script have an
> argument, i.e.
>
> ruby script.rb 3 2
>
> So far I have this:
>
> abort "Correct syntax is ruby [script].rb [number to exponentially
> multiply by] [exponent]" unless ARGV.size == 2
> var = gets.chomp
> var2 = gets.chomp
> puts (var.to_i ** var2)
>
> It's a simple exponential calculator.
>
> I get this error when trying to run it with 2 arguments (2 and 3).
>
> exponent.rb:2:in `gets': No such file or directory - 2 (Errno::ENOENT)
> from exponent.rb:2:in `gets' from exponent.rb:2:in `<main>'
>
>

gets reads from an IO stream, not the arguments on the command line:

http://ruby-doc.org/core/classes/IO.html#M002272

The arguments on the command line are stored in the ARGV array. That's why you check ARGV's size to verify that there are only 2 arguments.

So the code should read the options out of the ARGV array, not trying to gets things. There are a couple of ways to do this. My favourite looks like:

var = ARGV.shift
var2 = ARGV.shift

A couple of more complicated ways, but more flexible ways, of getting command line arguments are optionparser and getopts. I typically use getopts, with no real rationale behind it than that I learned it that way first.




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