From: ara.t.howard@...
Date: 2006-03-05T01:00:43+09:00
Subject: Re: Intercepting STDERR

On Sat, 4 Mar 2006, Phrogz wrote:

> Thanks so much, Ara. That's almost perfect, except that the exitstatus
> seems to be eaten. No matter what happens, I get a clean 0 exitstatus.
> For example:
>
> require 'open3'
>
> `lua xxx`
> #=> lua: cannot open xxx: No such file or directory
>
> p $?.exitstatus
> #=> 1
>
> output, errors = '', ''
> p Open3::popen3( "lua xxx" ){ |i,o,e|
> 	i.close
> 	o.each { |line| output << line }
> 	e.each { |line| errors << line }
> 	$?.exitstatus
> }
> #=> 0
>
>
> I can mostly infer the failure based on whether or not messages came to
> stderr, but it'd be nice to know for sure.
>
>

right you are.  if you check out ruby-1.8.4/lib/open3.rb you'll see :

...
     pid = fork{
       # child
       fork{
 	# grandchild
         ...
         ...
         ...
       }
       exit!(0)        # check this out
     }
...

so you'll never see an error.  my open 4 package fixes this - i actually just
made a release a few weeks ago to support throwing and exception when the exec
fails.  here's an example (it's on rubyforge):

     harp:~ > cat a.rb
     IO::popen("gem install open4 -r -y"){|pipe| pipe.read} and puts "installed open4..."
     require "rubygems"
     require "open4"

     def spawn cmd, opts = {}
       getopt = lambda{|o,*d| opts[o] || opts[o.to_s] || opts[o.to_s.intern] || d.shift}
       stdin = getopt["stdin"] || getopt[0, ""]
       stdout = getopt["stdout"] || getopt[1, ""]
       stderr = getopt["stderr"] || getopt[2, ""]

       Open4::popen4(cmd) do |cid,i,o,e|
         stdin.each{|line| i << line}
         i.close
         o.each{|line| stdout << line }
         e.each{|line| stderr << line }
       end

       [$?.exitstatus, stdout, stderr]
     end


     bt =
       lambda{|e| STDERR.puts %Q[#{ e.message } (#{ e.class })\n#{ e.backtrace.join "\n" }\n]}


     argvs =
       ["fubar"],
       ["ruby does-not-exist"],
       ["ruby", {"stdin" => "p 42"}]


     argvs.each do |argv|
       cmd, opts = argv
       puts
       puts "--- spawn( #{ cmd.inspect }, #{ opts.inspect } ) ---"
       p( spawn(*argv) ) rescue bt[$!]
       puts
       puts
     end



     harp:~ > ruby a.rb
     installed open4...

     --- spawn( "fubar", nil ) ---
     No such file or directory - fubar (Errno::ENOENT)
     /home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:75:in `exec'
     /home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:75:in `popen4'
     /home/ahoward//lib/ruby/site_ruby/1.8/open4.rb:57:in `popen4'
     a.rb:11:in `spawn'
     a.rb:36
     a.rb:32



     --- spawn( "ruby does-not-exist", nil ) ---
     [1, "", "ruby: No such file or directory -- does-not-exist (LoadError)\n"]



     --- spawn( "ruby", {"stdin"=>"p 42"} ) ---
     [0, "42\n", ""]


hth.

i'd sure like to get this in the stdlib...

-a

-- 
judge your success by what you had to give up in order to get it.
- h.h. the 14th dali lama