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comp.lang.ruby

Ruby and *NIX environment variables

Ben Zealley

7/25/2006 5:20:00 PM

'allo,

Context: I'm replacing parts of an existing collection of shell scripts
and bits of Perl with a unified Ruby system (this despite little to no
understanding of either of the first two...). In one particular case, I
have a script (values.sh) which contains instructions like

VARIABLE=VALUE

The results of which I would really like to be able to see from Ruby.
I'm told that it's setting environment variables and that the values
are visible from the calling script because it invokes values.sh with a
leading period, which causes them to share an environment - fair
enough.

The question is this: if I call values.sh from within Ruby (with a
leading period) will I be able to see the updated environment variables
after it returns, or is this behaviour specific to when one shell
script calls another? (They're ksh scripts, if that information is
helpful)

I'd test this myself, but I have no access to any *NIX boxes until I've
completed the design stage of this project... and my history is sadly
Windowsy. :(

Cheers

--
Ben
8 Answers

Logan Capaldo

7/25/2006 5:38:00 PM

0


On Jul 25, 2006, at 1:25 PM, Ben Zealley wrote:

> The question is this: if I call values.sh from within Ruby (with a
> leading period) will I be able to see the updated environment
> variables
> after it returns, or is this behaviour specific to when one shell
> script calls another? (They're ksh scripts, if that information is
> helpful)

The second one, fortunately or unfortunately as the case may be. .
<script> is the source command in ksh, it's equivalent to typing the
contents of the shell script in the original file. Theres no why for
a child process to affect it's parent's environment. OTOH if
values.sh has simple value parts you may be able to parse the script
with ruby to pull in the info.

Ara.T.Howard

7/25/2006 5:46:00 PM

0

Ben Zealley

7/25/2006 6:09:00 PM

0


>
> i do something like this
>
[snip]

Thanks very much - I shall probably use that :D

--
Ben
"Never worry about theory as long as the machinery does what it's
supposed to do."
- Robert Heinlein

Logan Capaldo

7/25/2006 6:32:00 PM

0


On Jul 25, 2006, at 1:45 PM, ara.t.howard@noaa.gov wrote:

> On Wed, 26 Jul 2006, Logan Capaldo wrote:
>
>>
>> On Jul 25, 2006, at 1:25 PM, Ben Zealley wrote:
>>
>>> The question is this: if I call values.sh from within Ruby (with a
>>> leading period) will I be able to see the updated environment
>>> variables
>>> after it returns, or is this behaviour specific to when one shell
>>> script calls another? (They're ksh scripts, if that information is
>>> helpful)
>>
>> The second one, fortunately or unfortunately as the case may be. .
>> <script>
>> is the source command in ksh, it's equivalent to typing the
>> contents of the
>> shell script in the original file. Theres no why for a child
>> process to
>> affect it's parent's environment. OTOH if values.sh has simple
>> value parts
>> you may be able to parse the script with ruby to pull in the info.
>
> i do something like this
>
> require 'session'
>
> bash = Session::Bash.new
>
> stdout, stderr = bash.execute 'ruby -r yaml -e" y ENV "'
> before = YAML.load stdout
>
> stdout, stderr = bash.execute '. values.sh'
>
> stdout, stderr = bash.execute 'ruby -r yaml -e" y ENV "'
> after = YAML.load stdout
>
> updated = after.to_a - before.to_a
>
> updated.each{|k,v| ENV[k] = v}
>
> which saves you having to parse the file and works even if it's
> horrifically
> complicated...
>
Very neat hack. Only thing I would change would be to do:

...
after = YAML.load stdout
ENV.update(after)




> -a
> --
> suffering increases your inner strength. also, the wishing for
> suffering
> makes the suffering disappear.
> - h.h. the 14th dali lama
>

Ben Zealley

7/25/2006 6:39:00 PM

0


Erm, *puts on his newbie shirt* I don't seem to have the "session"
package, maybe because this is one-click Ruby for Windows - is it
included by default with the *nix version, or do I need to get it from
somewhere? If the latter, where? I assume
http://rubyforge.org/projec... is the homepage, but there's
nothing there...

Cheers

--
Ben


ara.t.howard@noaa.gov wrote:
> On Wed, 26 Jul 2006, Logan Capaldo wrote:
>
> >
> > On Jul 25, 2006, at 1:25 PM, Ben Zealley wrote:
> >
> >> The question is this: if I call values.sh from within Ruby (with a
> >> leading period) will I be able to see the updated environment variables
> >> after it returns, or is this behaviour specific to when one shell
> >> script calls another? (They're ksh scripts, if that information is
> >> helpful)
> >
> > The second one, fortunately or unfortunately as the case may be. . <script>
> > is the source command in ksh, it's equivalent to typing the contents of the
> > shell script in the original file. Theres no why for a child process to
> > affect it's parent's environment. OTOH if values.sh has simple value parts
> > you may be able to parse the script with ruby to pull in the info.
>
> i do something like this
>
> require 'session'
>
> bash = Session::Bash.new
>
> stdout, stderr = bash.execute 'ruby -r yaml -e" y ENV "'
> before = YAML.load stdout
>
> stdout, stderr = bash.execute '. values.sh'
>
> stdout, stderr = bash.execute 'ruby -r yaml -e" y ENV "'
> after = YAML.load stdout
>
> updated = after.to_a - before.to_a
>
> updated.each{|k,v| ENV[k] = v}
>
> which saves you having to parse the file and works even if it's horrifically
> complicated...
>
> -a
> --
> suffering increases your inner strength. also, the wishing for suffering
> makes the suffering disappear.
> - h.h. the 14th dali lama

Ara.T.Howard

7/25/2006 7:02:00 PM

0

Ara.T.Howard

7/25/2006 8:58:00 PM

0

Ben Zealley

7/26/2006 7:32:00 PM

0

Well, I've bullied them into giving me access to a box, and got Ruby,
RubyGems and session installed and apparently working - by reference to
about three *nix newbie tutorials, but still, it's working :)

In the name of simplicity (my manager is unlikely to be happy with
anything as complex-looking as the second code sample you gave me,
which did work - thankyou!), I'd like to use your original example.

However, I'm getting the following error:

[root@pc2461 ~]# ruby ara.rb
ara.rb:18: warning: default `to_a' will be obsolete
ara.rb:18: warning: default `to_a' will be obsolete
ara.rb:22:in `[]=': can't convert Object into String (TypeError)
from ara.rb:22
from ara.rb:22

I've tried playing around a bit but I can't seem to get much more than
that. Although "updated" ends up as an Array it only contains one value
(which is just of type Object, and doesn't correspond to any obvious
objects like "nil"...). (I've wrapped the "real" .sh I want to capture
variables from - it sets 8) Do you have any guesses as to why that's
happened?

Thanks so much for taking the time to help me with this!

--
Ben
"Life is "trying things to see if they work"." - Ray Bradbury