Running another ruby script from a ruby script

Question

In ruby, is it possible to specify to call another ruby script using the same ruby interpreter as the original script is being run by?

For example, if a.rb runs b.rb a couple of times, is it possible to replace

system("ruby", "b.rb", "foo", "bar")

with something like

run_ruby("b.rb", "foo", "bar")

so that if you used ruby1.9.1 a.rb on the original, ruby1.9.1 would be used on b.rb, but if you just used ruby a.rb on the original, ruby would be used on b.rb?

I'd prefer not to use shebangs, as I'd like it to be able to run on different computers, some of which don't have /usr/bin/env.

Edit: I didn't mean load or require and the like, but spawning new processes (so I can use multiple CPUs).

Answer 1

require "b.rb"

will execute the contents of b.rb (you call leave off the ".rb", and there is a search path). In your case, you would probably do something like:

a.rb:

require "b.rb";
b("Hello", "world")

b.rb:

def b(first, second)
  puts first + ", " + second
end

Note that if you use require, Ruby will only load and execute the file once (every time you call load it will be reloaded), but you can call methods defined in the file as many times as you want.

As things get more complex, you will want to move towards an object-oriented design.

EDIT: In that case, you should look into Ruby threading. A simple example is:

a.rb:

require "b";
t1 = Thread.new{b("Hello", "world");}
t2 = Thread.new{b("Hello", "galaxy");}
t1.join
t2.join

b.rb:

def b(first, second)
  10.times {
    puts first + ", " + second;
    sleep(0.1);
  }
end

Answer 2

Avdi Grimm wrote a series of articles on the Devver blog about different ways to start Ruby subprocesses last summer:

• A Dozen (or so) Ways to Start Subprocesses in Ruby: Part 1
• A Dozen (or so) Ways to Start Subprocesses in Ruby: Part 2
• A Dozen (or so) Ways to Start Subprocesses in Ruby: Part 3
• Beware of pipe duplication in subprocesses

[Note: it appears that part 4 hasn't been published yet.]

Answer 3

http://en.wikibooks.org/wiki/Ruby_Programming/Running_Multiple_Processes might help

Answer 4

The require trick is a good idea, assuming the script in question doesn't choke trying to redefine any constants you may have set, or calling methods on objects you may have runtime monkey patched to no longer honor their standard contracts.

In either case, the problem is less the approach than it is the code in the scripts themselves. Show good manners, put your constants in a namespace, and don't monkey patch the runtime desctructively.

To ensure the script in question doesn't mess with the runtime of your calling script, and to guard against the chance it might call Kernel/Process.exit() somewhere, try the following

pid=Process.fork do
    require 'script.rb'
    Process.exit
end
ignored, status = Process.waitpid2(pid, Process::WNOHANG)
puts "script.rb PID #{pid} exited, exit status: #{status.exitstatus}" 

For more advanced things like writing to its stdin stream or reading from its stdout or stderr streams, use the Open4 gem.