time format in ruby
http://www.ruby-doc.org/core/classes/Time.html#M000236
1 %a - The abbreviated weekday name (``Sun'') 2 %A - The full weekday name (``Sunday'') 3 %b - The abbreviated month name (``Jan'') 4 %B - The full month name (``January'') 5 %c - The preferred local date and time representation 6 %d - Day of the month (01..31) 7 %H - Hour of the day, 24-hour clock (00..23) 8 %I - Hour of the day, 12-hour clock (01..12) 9 %j - Day of the year (001..366) 10 %m - Month of the year (01..12) 11 %M - Minute of the hour (00..59) 12 %p - Meridian indicator (``AM'' or ``PM'') 13 %S - Second of the minute (00..60) 14 %U - Week number of the current year, 15 starting with the first Sunday as the first 16 day of the first week (00..53) 17 %W - Week number of the current year, 18 starting with the first Monday as the first 19 day of the first week (00..53) 20 %w - Day of the week (Sunday is 0, 0..6) 21 %x - Preferred representation for the date alone, no time 22 %X - Preferred representation for the time alone, no date 23 %y - Year without a century (00..99) 24 %Y - Year with century 25 %Z - Time zone name 26 %% - Literal ``%'' character