How to check process is running from its pid number, in Ruby

#check_ocpps_server_status.rb
PID = %x{ cat tmp/pids/http_server.pid }
# => 19006
result = %x{ ps aux | grep http_server | grep #{PID} }
# =>
# alfredo  19006  2.7  1.1 267096 45088 pts/8    Sl   13:08   0:00 ruby lib/ocpps/http_server.rb
# alfredo  19060  0.0  0.0 113544  2948 pts/8    S+   13:08   0:00 sh -c  ps aux | grep http_server | grep 19006
running = false
result.split("\n").each{|line| running = true if /http_server.rb/=~line}
puts running ? ">>>> :-) OK - OCPP SERVER RUNNING" : ">>>> :( OCPP SERVER NOT RUNNING !!!"

Note: used in Etecnic webapp