use wmctrl and gtk-launch to bring an existing window to the front or launch the app

switch_or_launch.rb

#!/usr/bin/ruby

base_cmd = ARGV[0]
cmd_pattern = Regexp.new(base_cmd)
running = `wmctrl -lx`.lines.grep(cmd_pattern)

if running.any?
  window_id = running.first.match(/0x[0-9a-f]{8}/)[0]
  exec "wmctrl -ia #{window_id}"
else
  puts "starting: #{ARGV.join(' ')}"
  exec "gtk-launch", *ARGV
end