# ./script.pl -h

USAGE : ./script.pl -t <D|W|M|S> -s [DATE]

  -t       specifies the type of period for which the information
           is retrieved
     D     scale : day
     W     scale : week
     M     scale : month
     S     scale : a few seconds

  -s       start date to retrieve data
           (format YYYYMMDD)

  -h       displays this help then stops

# ./script.pl -t D -s 20121015
period OK
date OK