periodlength.rb

stream = File.open(ARGV.shift)
blksize = stream.stat.blksize
bytes_required = 32
start = stream.read(bytes_required)
match = String.new
buffer = String.new

while stream.read(blksize, buffer)
    buffer.bytes.with_index do |byte, index|
        match.concat(byte)
        start.start_with?(match) or next match.clear
        match.eql?(start) and break begin
            puts("Sequence restarted at:")
            puts(stream.pos-blksize+index-bytes_required)
            abort(match)
        end
    end or break
end

puts("Found nothing.")