This is my script to generate OSMs out of all of a country's POLY files.

poly_to_osm.rb

#!/usr/bin/env ruby

Dir.glob('poly/*.poly').each_slice(50) do |group|
  bp_wx = ''

  group.each do |poly_file|
    file         = File.basename(poly_file, '.poly')
    city, region = file.split('_')
    bp_wx << "--buffer bufferCapacity=50000"\
             " --bp file='poly/#{city}_#{region}.poly'"\
             " --buffer bufferCapacity=50000"\
             " --wx file='done/#{city}_#{region}.osm' "
  end

  system("time osmosis/bin/osmosis --read-pbf-fast workers=20"\
         " file='source/COUNTRY-latest.osm.pbf' --tee #{group.count}"\
         " #{bp_wx}")
end