How to make specific command line programs usable by Ruby code running in Automator

There are many ways in ruby to make a system call.

I'm currently using open3 in a method like this:

def run_system_command { |system_command|
   
  stdout_str = ""
  stderr_str = ""
  status = ""
 
  Open3.popen3(system_command) do |stdin, stdout, stderr, wait_thr|
     stdin.close                
     stdout_str = stdout.read   # read stdout to string. note that this will block until the command is done!
     stderr_str = stderr.read   # read stderr to string
     status = wait_thr.value    # will block until the command finishes; returns status that responds to .success? etc
  end
 
  return stdout_str, stderr_str, status
}

It works fine when running basic system commands like tar or ls or cd etc...

But when I try to run a program like ios-deploy from an Automator 'Run Shell Script', I don't get any results:

(Assume the run_system_command method is defined in the block. Automator text fields don't expand so I couldn't show you the whole thing)

I get no output from such a call, which makes me think that making a system call in Ruby doesn't see the ios-deploy program.

Note that I've made sure that I can get output from Ruby in general by using 'Set Value of Variable' and 'Display Notification' actions in a simple "Hello World" 'Run Shell Script' action.

How can I tell ruby how to use / where to find the program?

Some kind of path adjustment? I'm not sure where to make such a change when calling Ruby in this way.

Update: I'm able to get the command to work by using the full path to the program:

/usr/local/bin/ios-deploy

Is there a way to tell Ruby/Automator where to find that program without having to explicitly use the path prefix every time?

> Is there a way to tell Ruby/Automator where to find that program without having to explicitly use the path prefix every time?

Kind of. Automator runs Ruby (as well as the other shell scripts) using an environment with PATH set to /usr/bin:/bin:/usr/sbin:/sbin, i.e. it will only search for executables in /usr/bin, /bin, /usr/sbin and /sbin.

I don't see any way to configure the environment in Automator, but at least you can modify the environment in Ruby via ENV#[]=, e.g.:

ENV['PATH'] = "/usr/local/bin:#{ENV['PATH']}"

This way, executables in /usr/local/bin will become available when running a shell command:

Open3.popen3 also accepts environment variables as an argument: (see the docs for Process.spawn)

require 'open3'

env = { 'PATH' => "/usr/local/bin:#{ENV['PATH']}" }
command = 'brew --version'

Open3.popen3(env, command) do |stdin, stdout, stderr, wait_thr|
  # ...
end