starttime: find the starttime of the given process

#!/usr/bin/ruby -WKu

# Find the starttime of the process pid
# http://qiita.com/isaoshimizu/items/ee555b99582f251bd295
def starttime(pid)
  run = proc {|cmd|
    out = `#{cmd}`
    raise "Failed to run: #{cmd}" if !$?.success?
    out
  }

  btime = run["sed -n 's/^btime //p' /proc/stat"].chomp.to_i
  tck = run['getconf CLK_TCK'].chomp.to_i
  start = run["cut -d ' ' -f22 /proc/#{pid}/stat"].chomp.to_f
  btime + start / tck
end

if $0 == __FILE__
  die = proc {|msg|
    $stderr.puts msg
    exit false
  }
  die['usage: starttime (pid)'] if $*.size != 1 || /\A\d+\z/ !~ (pid = $*[0])
  puts starttime(pid) rescue die[$!]
end