Running sub-processes in Ruby

ruby-sub-processes.md

Resources:

• https://www.rubyguides.com/2018/12/ruby-system/
• https://medium.com/zendesk-engineering/running-a-child-process-in-ruby-properly-febd0a2b6ec8
• https://stackoverflow.com/questions/29845778/starting-a-process-and-killing-it-from-ruby-on-rails-app-without-leaving-zombie
• Executing and killing ruby parallel background jobs

Starting a Process and killing it

Process Ruby Doc

The child process can exit using Kernel.exit! to avoid running any at_exit functions. The parent process should use Process.wait to collect the termination statuses of its children or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.

To Be Tested

def start
  @pid = IO.popen("sleep").pid
  # @pid = fork { `sleep` }
end

def stop
  Process.kill(9, @pid)
  Process.wait(@pid)
end

Synchronous calls

From article

Method #1: The Backtick Operator

returns the output of the command

`ls`
%x|ls|

Method #2: Kernel#system

returns boolean if the command is successful

• true (command worked)
• false (command errrors out)
• nil (command not found)

system("ls")

Forks

Method #3: Kernel#fork (aka Process.fork)

This will run ls on another process & display its output

pid = fork { exec("ls") }
Process.wait(pid)

From article

Method #4: Opening a pipe

To Do

Method #5: Forking to a pipe

To Do

From article

Method #6: Open3

r = IO.popen("irb", "r+")
r.write "puts 123 + 1\n"
3.times { puts r.gets }
r.write "exit\n"

Method #7: PTY

Method #8: Shell