Windows Ruby get PID from process name

Question

So I do realize a similar question has been asked Find a process ID by name but the thing is, it really returns all PIDs with their names, including the spawned children of that process. My question is how can I only get the PID of the parent process and not one of it's children?

Answer 1

The sys-proctable gem can do that, here is a minimal example for getting the PID of the ruby.exe process on the system:

require 'sys/proctable'

def get_process_id(name)
    Sys::ProcTable.ps.detect{|p| p.name == name}&.pid
end

puts get_process_id("ruby.exe")

That doesn't guarantee you will find the parent process tho, you will instead get the process with the lowest PID.

To actually find the "root process", you need to further select processes by checking if their parent process is either non-existent or a different process:

require 'sys/proctable'

def get_parent_process_id(name)
    # generate a hash mapping pid -> process info
    processes = Sys::ProcTable.ps.map{|p| [p.pid, p]}.to_h

    # find the first matching process that has either no parent or a parent
    # that doesn't match the process name we're looking for
    processes.values.each do |p| 
        next if p.name != name

        if processes[p.ppid].nil? || processes[p.ppid].name != name
            return p.pid
        end
    end

    nil
end

puts get_parent_process_id("chrome.exe")