Masoud, I don't believe you need to interpolate the op, you can just use
op, for example:

if op == "Q"

Hope this helps,

Anna

On Sun, Dec 2, 2012 at 4:43 PM, Masoud Ahmadi <lists / ruby-forum.com> wrote:

> puts("give me the command to execute or press Q to quit")
>       op=gets
>       if "#{op}" == "Q"
>         then
>         Kernel.exit(0)
>       else
>         value = `#{op}`
>         puts "#{value}"
>       end
>