%a - abbreviated weekday name
%A - full weekday name
%b - abbreviated month name
%B - full month name
%c - date and time in the form Mon Apr 15 13:25:31 1996
%d - day of the month as a number ( 01-31 ).
%H - hour as a number ( 00-23 , uses 24 hour clock )
%I - hour as a number ( 00-12 , uses 12 hour clock ) (uppercase i)
%j - day of the year as a number ( 001-366 )
%m - month as a number ( 01-12 )
%M - minute as a number ( 00-59 )
%p - AM/PM designation for a 12 hour clock
%S - second as a number ( 00-59 )
%U - week number of the year ( with Sunday as the first day of the first week ) as a number ( 00-53 )
%w - weekday as a number ( 0 (Sunday) - 6 ( Saturday ) )
%W - week number of the year ( with Monday as the first day of the first week ) as a number ( 00-53 )
%x - date the form Apr 15 1996
%X - time in the form 1:32:03.
%y - year without the century ( 00-99 )
%Y - year with the century as in 1999.
%Z - current time zone ( if available )
%% - prints %.