ruby time format

 %a - The abbreviated weekday name (``Sun'')
  %A - The  full  weekday  name (``Sunday'')
  %b - The abbreviated month name (``Jan'')
  %B - The  full  month  name (``January'')
  %c - The preferred local date and time representation
  %C - Century (20 in 2009)
  %d - Day of the month (01..31)
  %D - Date (%m/%d/%y)
  %e - Day of the month, blank-padded ( 1..31)
  %F - Equivalent to %Y-%m-%d (the ISO 8601 date format)
  %h - Equivalent to %b
  %H - Hour of the day, 24-hour clock (00..23)
  %I - Hour of the day, 12-hour clock (01..12)
  %j - Day of the year (001..366)
  %k - hour, 24-hour clock, blank-padded ( 0..23)
  %l - hour, 12-hour clock, blank-padded ( 0..12)
  %L - Millisecond of the second (000..999)
  %m - Month of the year (01..12)
  %M - Minute of the hour (00..59)
  %n - Newline (\n)
  %N - Fractional seconds digits, default is 9 digits (nanosecond)
          %3N  millisecond (3 digits)
          %6N  microsecond (6 digits)
          %9N  nanosecond (9 digits)
  %p - Meridian indicator (``AM''  or  ``PM'')
  %P - Meridian indicator (``am''  or  ``pm'')
  %r - time, 12-hour (same as %I:%M:%S %p)
  %R - time, 24-hour (%H:%M)
  %s - Number of seconds since 1970-01-01 00:00:00 UTC.
  %S - Second of the minute (00..60)
  %t - Tab character (\t)
  %T - time, 24-hour (%H:%M:%S)
  %u - Day of the week as a decimal, Monday being 1. (1..7)
  %U - Week  number  of the current year,
          starting with the first Sunday as the first
          day of the first week (00..53)
  %v - VMS date (%e-%b-%Y)
  %V - Week number of year according to ISO 8601 (01..53)
  %W - Week  number  of the current year,
          starting with the first Monday as the first
          day of the first week (00..53)
  %w - Day of the week (Sunday is 0, 0..6)
  %x - Preferred representation for the date alone, no time
  %X - Preferred representation for the time alone, no date
  %y - Year without a century (00..99)
  %Y - Year with century
  %z - Time zone as  hour offset from UTC (e.g. +0900)
  %Z - Time zone name
  %% - Literal ``%'' character

   t = Time.now                        #=> 2007-11-19 08:37:48 -0600
   t.strftime("Printed on %m/%d/%Y")   #=> "Printed on 11/19/2007"
   t.strftime("at %I:%M%p")            #=> "at 08:37AM"