Forum: Ruby Executing shell commands from Ruby... again.

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Kevin S. (Guest)
on 2007-03-16 22:48
I'm not only very new to Ruby, but also to server side programming in
general, so I'm having a hard time finding a good place to look for
solutions.

I've seen a number of posts regarding the execution of shell commands
from Ruby / Rails, but I can't figure out a way to call a shell process
and retain a reference to it so that I can execute successive commands.
I need to do this on a Windows machine, so a typical batch file might be
constructed like this:

  echo off
  cd path\executabledir
  <command> -S <param> <input> <output>

where anything in <> needs to be dynamically populated.  I'm able to
execute a batch file with the information hard-coded using
IO.popen("batchfile"), but I need to be able to manipulate the shell
commands before running them.

If anyone knows of any fitting resources that a newbie to this entire
concept could understand, please let me know.

Thanks.
Jan F. (Guest)
on 2007-03-16 23:00
(Received via mailing list)
Kevin S. schrieb:
> I need to do this on a Windows machine, so a typical batch file might be
> constructed like this:
>
>   echo off
>   cd path\executabledir
>   <command> -S <param> <input> <output>
>
> where anything in <> needs to be dynamically populated.
How about this:

# -- BEGIN OF EXAMPLE

# setting command, param, input, output
# ...
cmd = <<END_OF_STRING
echo off
cd path\executabledir
#{command} -S #{param} #{input} #{output}
END_OF_STRING

system(cmd)

# -- END OF EXAMPLE


regards
Jan
Alexey V. (Guest)
on 2007-03-16 23:10
(Received via mailing list)
On 3/16/07, Kevin S. <removed_email_address@domain.invalid> wrote:
>
> I can't figure out a way to call a shell process
> and retain a reference to it so that I can execute successive commands.
> I need to do this on a Windows machine,


While trivial on *nix, this task is not as easy as it should be on
Windows.
I am specifically talking about having a reference to the child process
and
doing anything with it. It involves "really close to the metal" Win32
API
calls.

For an example, have a look at the implementation of
InstikiController.startin the following file:
  http://dev.instiki.org/browser/instiki/trunk/test/...

I probably don't understand the second half of your question, because I
read
it as "how do I dynamically construct strings from variables". This is
covered in the first 100 pages of every language tutorial, so nobody
should
ever have to ask this question on the list.

Alex
Kevin S. (Guest)
on 2007-03-16 23:25
Jan F. wrote:
> How about this:
>
> # -- BEGIN OF EXAMPLE
>
> # setting command, param, input, output
> # ...
> cmd = <<END_OF_STRING
> echo off
> cd path\executabledir
> #{command} -S #{param} #{input} #{output}
> END_OF_STRING
>
> system(cmd)
>
> # -- END OF EXAMPLE

That makes perfect sense, but for some reason I'm getting this error:
: can't find string "END_OF_STRING" anywhere before EOF
: syntax error, unexpected $end, expecting tSTRING_CONTENT or
tSTRING_DBEG or tSTRING_DVAR or tSTRING_END

I'm still working on it, but this solution seems to be ideal as long as
I can get it to function properly.

Alex, you're exactly right, I certainly have no problems using variables
to construct a String. :) I was merely saying that the batch file
solution was insufficient because I can't create its content
dynamically.  Thanks for your reply, I'll check out the file you
provided.
Robert K. (Guest)
on 2007-03-16 23:35
(Received via mailing list)
On 16.03.2007 21:58, Jan F. wrote:
>
> system(cmd)
>
> # -- END OF EXAMPLE

You can even combine that:

system <<CMD
echo off
cd path
#{command} -S #{arg}
CMD

And if you need a longer running shell that executes multiple commands
you can use popen:

# IO.popen("bash", "r+") do |io|
IO.popen("cmd", "r+") do |io|
   th = Thread.new(io) do |chan|
     chan.each {|line| puts line}
   end

   # io.puts "ls -l"
   io.puts "dir"
   io.puts "exit"
   io.close_write

   th.join
end

Kind regards

  robert
Stefano C. (Guest)
on 2007-03-16 23:38
(Received via mailing list)
Alle venerdì 16 marzo 2007, Kevin S. ha scritto:
> That makes perfect sense, but for some reason I'm getting this error:
> : can't find string "END_OF_STRING" anywhere before EOF
> : syntax error, unexpected $end, expecting tSTRING_CONTENT or
>
> tSTRING_DBEG or tSTRING_DVAR or tSTRING_END

Are you sure that the second END_OF_STRING is right at the beginning of
the
line? What I mean is that the following code

cmd = <<END_OF_STRING
  text
  END_OF_STRING

will produce exactly the error message you get, because the closing
END_OF_STRING is not at the beginning of the line (there are some
whitespaces
before it). The correct form is:

cmd = <<END_OF_STRING
  text
END_OF_STRING

If you really want some spaces before the closing END_OF_STRING, you
should
use the <<- form:

cmd = <<-END_OF_STRING
  text
  END_OF_STRING

which allows spaces before the closing tag.

I hope this helps

Stefano
Kevin S. (Guest)
on 2007-03-17 00:37
Stefano C. wrote:
> Alle venerdì 16 marzo 2007, Kevin S. ha scritto:
> Are you sure that the second END_OF_STRING is right at the beginning of
> the
> line?
>
> ...
>
> If you really want some spaces before the closing END_OF_STRING, you
> should
> use the <<- form

Well, I didn't have any indenting going on, but the <<- syntax fixed the
problem anyway.  It's probably just my crappy editor.

It would seem that everything is working - the system method executes
and returns true, and if I print out the command, it's identical to what
was in my batch file, but the batch file creates the desired output, and
the system method creates nothing.

Could it be an issue of each line hitting the shell before the previous
line has completed?  I need to research Robert's IO.popen solution to
get a better grasp of what's happening there - perhaps that method is
more appropriate.

Thanks, everybody, for all your help.
Robert K. (Guest)
on 2007-03-17 11:11
(Received via mailing list)
On 16.03.2007 23:37, Kevin S. wrote:
> It would seem that everything is working - the system method executes
> and returns true, and if I print out the command, it's identical to what
> was in my batch file, but the batch file creates the desired output, and
> the system method creates nothing.

The output of system goes to stdout.  If you want to capture it the
popen method is better.

> Could it be an issue of each line hitting the shell before the previous
> line has completed?

No, normally not.  Unless of course you tell the shell to put things
into background.

 >  I need to research Robert's IO.popen solution to
> get a better grasp of what's happening there - perhaps that method is
> more appropriate.

Kind regards

  robert
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