From: Mark Wilson <mwilson13@...>
Date: 2003-08-26T05:02:05+09:00
Subject: Re: Ruby launching system apps?


On Monday, August 25, 2003, at 01:25 PM, Dan wrote:

> I have a UNIX machine and I want a ruby app that can launch UNIX 
> commands
> like awk or sed...how would I implement this?
>
> use Shell.new?

I've found that when you have a program that makes use of UNIX commands 
within various classes and methods that system and `` calls can lead to 
synchronization problems -- and that such problems can be solved by 
using the Shell#transact method.

Here's an example:

class Document

Shell.def_system_command("lynx")

   attr_reader :path

   def initialize(path)
     @path = path
   end

   def html_to_text_stdout
# the following line is needed because @path is not in the scope of the 
transact block below
     path = @path
     html_to_text = String.new
     shell = Shell.new
     shell.transact do
       html_to_text = (shell.lynx("-dump", path)).to_s
     end
     html_to_text
   end

end

I agree with Gennady that you will frequently be better off using 
native Ruby classes and methods for many things, particularly in-memory 
string manipulation, even if comparable tools are available through a 
Unix command.

Regards,

Mark