From: Moritz Reiter <mreiter@...>
Date: 2006-11-25T01:20:52+09:00
Subject: Re: invoke system command from within a method

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Jan Svitok wrote:
> On 11/24/06, Moritz Reiter <mreiter@agrav.org> wrote:
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>> Moritz Reiter wrote:
>> > Hi all,
>> >
>> > I am new to Ruby and want to make a Ruby script for the network
>> > configuration of my notebook as an exercise. Now I encountered a
>> problem
>> > which is pretty strange to me:
>> >
>> > I want to invoke '/etc/init.d/networking restart' from within my Ruby
>> > program. If I create a file with the line
>> >
>> > %x{ /etc/init.d/networking restart }
>> >
>> > it works like I would expect. The networking init script gets invoked
>> > and correctly processed.
>> >
>> > But if I do something like this:
>> >
>> > -->8--
>> > class Netconf
>> >       def restart
>> >               puts %x{ /etc/init.d/networking restart }
>> >       end
>> > end
>> >
>> > netconf = Netconf.new
>> > netconf.restart
>> > --8<--
>> >
>> > I get some output from the init script but it doesn't seem to actually
>> > do anything. It does not reconfigure my eth's in oppostion to the
>> > behaviour described above if don't make the system call from within a
>> > method.
>> >
>> > I would be very glad if anyone could give me a hint or point me to some
>> > documentation to enlighten me.
>> >
>> > Best Regards,
>> >
>>
>> Okay, now I know what went wrong. I should have told you the whole
>> story: In my script I rewrite /etc/network/interfaces and then invoke
>> the init script. My fault was, that I didn't close the File handler for
>> /etc/network/interfaces before starting the init script. So the init
>> script invoked ifdown and ifup but ruby did not write the new content of
>> /etc/network/interfaces to the harddisk yet, so ifup had no useful data
>> to do its job.
>>
>> Damn, I learned my lesson: Always close your files as soon as you have
>> finisehd writing to them.
> 
> This is where the block variant of File.open comes handly - you don't
> have to close the file even in the case of exception.
> 
> File.open('blabla', 'w') do |f|
>  f.write('blabla')
> end
> 

Cool, thanks for the hint!

- --
Moritz Reiter <mreiter@agrav.org>

GPG key fingerprint:
https://luna.agrav.org/~mo/gpg/

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