From: ara.t.howard@...
Date: 2006-02-03T04:59:16+09:00
Subject: [OT] Re: Chomping and stomping

On Fri, 3 Feb 2006, William James wrote:

> The error I get in a dos-box is The system cannot find the path specified.
>
> To produce the error you gave, I must do it this way: ruby a.rb < nul:
>
> When you post something that depends upon a particular operating system, you
> need to make that dependency clear.

indeed.  that's what specifying cat and /dev/null does in and least four ways:

   cat, the most ubiquitous of unix programs => *nix
   / as file separator                       => *nix
   /dev file system                          => *nix
   /dev/null device                          => *nix

;-)

> It is reasonable to write a program that requires input.  It is not
> reasonable to expect a program that requires input to function properly when
> you deliberately deprive it of input.

that's not what is happening.  reading from /dev/null or nul is the same as
reading from an empty file.  the key point i was illustrating, and the bug in
the program, is that is fails at eof regardless if input is given.

for example, if i run this from the shell and type 'ctrl-d' to signal end of
input (on unix)

   harp:~ > cat a.rb
   def chomper
     until (xx = gets.chomp) == 'qq'
       puts "hit me with a squirell!"
     end
     xx
   end

   puts chomper


   harp:~ > ruby a.rb
   a.rb:2:in `chomper': private method `chomp' called for nil:NilClass (NoMethodError)
           from a.rb:8


running on an empty file does the same

   harp:~ > touch empty
   harp:~ > ruby a.rb < empty
   a.rb:2:in `chomper': private method `chomp' called for nil:NilClass (NoMethodError)
           from a.rb:8


as does running with some input

   harp:~ > echo 42 > input

   harp:~ > ruby a.rb < input
   hit me with a squirell!
   a.rb:2:in `chomper': private method `chomp' called for nil:NilClass (NoMethodError)
           from a.rb:8

in fact, it cannot be made to work with any input

it's important, imho only perhaps, to show working code (best done by actually
showing a run) unless that code is noted to be un-tested.  i make efforts to do
this for all examples i post:

   http://groups.google.com/group/comp.lang.ruby/search?q=howard+cat+a.rb&start=0&scoring=d&

some probably find it anoying but i make too many mistakes otherwise.

kind regards.

-a

-- 
happiness is not something ready-made.  it comes from your own actions.
- h.h. the 14th dali lama