From: Garry Offord <droffo@...>
Date: 2007-09-21T03:32:45+09:00
Subject: Re: Interactive System calls within Ruby Script

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Zylo:

The problem is the the command pass to the system call is executed in a
sub-shell, or child process. Any changes made in that sub-shell's
environment is *not* reflected back to the parent.  So changing the
directory in the sub-shell does not affect the parent's current working
directory.

When you do two system calls, they are executed in two separate sub-shells,
neither of which affect the other or the parent.

I normally change the directory in the parent before calling system or %x{}
etc:

    here = Dir.pwd
    Dir.chdir 'your-directory here'
    begin
        puts "You are now here: #{Dir.pwd}"
        system "your command"
    rescue Errno::ENOENT => e
        Dir.chdir here
    end

Hope that helps a bit.



On 9/20/07, ZyLo <Klauer@gmail.com> wrote:
>
> I'm not sure whether this is possible or not, but I know that Ruby
> allows you to make system calls in many different ways, and I
> generally use:
>
> system "echo Hello"
>
> or something when I want to call outside of the script.  What I would
> like to know is if it is possible to make these system calls
> interactive?  For instance, I was toying with directory manipulation
> using system "cd .." system "pwd", etc., and I noticed that no matter
> what the call, Ruby will always return to the same directory on the
> system "pwd" command.
>
> I was wondering if it is possible to send multiple commands so you
> could be a bit more interactive with it?  I know there are libraries
> out there to do this for me, but I am looking at this more from the
> standpoint that I'm not planning on using this ability for directory
> manipulation.
>
> Another thing I was wondering is whether you can get output from the
> terminal on system calls.  I tried somethign like this:
>
> system "pwd"
> gets directorystring
> puts directorystring
>
> Only my script doesn't get the input at all, and hangs(expecting an
> input I assume).
>
> How can you usefully use system for calling functions if it doesn't
> remember state(directory, for instance), or allow you to get back
> terminal information?
>
>
>

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