#!/usr/bin/env ruby
# daemon_with_pidfile
#
# Daemonize, write a pidfile, and exec the remainder of the command line.
def main(pidfile, cmd)
if middle_pid = Process.fork
# outer process
# Do not exit the outer process before the middle process finishes
Process.waitpid(middle_pid)
exit $?.exitstatus
end
if final_pid = Process.fork
# middle process
open(pidfile, 'w') { |f| f.puts final_pid }
exit
end
# Standard daemon things: become session leader, ignore SIGHUP, close stdin.
Signal.trap("HUP", "IGNORE")
Process.setsid
IO.new(0).close
exec(*cmd)
end
if ARGV.count < 2
abort "Usage: #$0 pidfile command [args...]"
end
pidfile = ARGV.shift
main(pidfile, ARGV)