From: Robert Klemme <shortcutter@...>
Date: 2011-02-03T21:01:35+09:00
Subject: Re: Bug in system()?

On Wed, Feb 2, 2011 at 5:49 PM, Anthony Wright <anthony@overnetdata.com> wrote:
> I've just hit a problem where the system() method to call an external program failed in a fairly unpredictable way, and I couldn't get any clues from within ruby to diagnose the problem, so I ended up debugging process.c to work out what the problem was.
>
> My code looks something like:
>
> system("/bin/tar --extract --directory=#{dir} --file=#{file}")
>
> if $?.exitstatus !=0
>    raise "tar unpack failed with exitstatus: #{$?.exitstatus}"
> end
>
> But it fails on the if because '$?' isn't being set by the failing system() method and so '$?' is nil.
>
> The problem ultimately boiled down to the fork() system call failing with ENOMEM (badly configured system, but that's another matter).
>
> Am I missing something here? Should there be a way to get errno from ruby, or am I missing other diagnostic information I could have used?
>
> Is there a bug in system()? Shouldn't it always set '$?' ?

You can use system's return value

irb(main):006:0> system '/bin/sh -c "exit 1"'
=> false
irb(main):007:0> system '/bin/sh -c "exit 0"'
=> true

system("/bin/tar --extract --directory=#{dir} --file=#{file}") or
raise "tar unpack failed"

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/