1. CIT 383: Administrative ScriptingSlide #1 CIT 383: Administrative Scripting DateTime

2. CIT 383: Administrative Scripting Topics 1.UNIX Time 2.Time Zones 3.Calendars 4.Ruby DateTime classes

3. CIT 383: Administrative Scripting UNIX Time UNIX time is seconds since the midnight, Jan 1, 1970. Most OS represent time as 32-bit signed int. Lowest time: 1901-12-13 Highest time: 2038-01-18 OS need to upgrade to 64 bits to avoid Y2038 problem.

4. CIT 383: Administrative Scripting Time Zones

5. CIT 383: Administrative Scripting UTC: Coordinated Universal Time Local time at royal observatory at Greenwich –GMT established at 1884 conference. –Prime meridian (0 degrees longitude.) International Atomic Time (TAI) –Based on atomic clock, established in 1958. –Includes leap seconds (December 31 2008 will be next) to account for lengthening of day as the Earth’s rotation slows. Time zones defined by offset from UTC.

6. CIT 383: Administrative Scripting Calendars Julian Calendar –Introduced by Julius Caesar in 46BC. –Reform of older Roman calendar system, which had leap months. –365 days, 12 months, leap day every 4 years. –Month Quintilius became July. Gregorian Calendar –Proposed by Aloysius Lilius. –Decreed by Pope Gregory XIII in 1582 (adopted by English 1752) –Dropped 10 days from Julian calendar. –Changed leap day rules Leap day every 4 years except if year is divisible by 100 except years divisible by 400 are still leap years.

7. CIT 383: Administrative Scripting Ruby DateTime classes Date Mutable date objects. Time Mutable time objects that also include date. DateTime Immutable objects with date and time.

8. CIT 383: Administrative Scripting Creating a Date object Date.today –Create Date object for current day. Date.new(year, month, day) –Create Date object based on year, month, and day. Date.parse(string) –Create Date object from date stored in string.

9. CIT 383: Administrative Scripting Creating a Time object Time.gm(year ) –Create time based on specified values. –Interpreted as GMT (UTC). Time.local(year ) –Create time based on specified values. –Interpreted as local set time zone. Time.new –Create Time object initialized to current time. Time.now –Same as Time.new.

10. CIT 383: Administrative Scripting Creating a DateTime object DateTime.new –Create Time object initialized to current time. DateTime.now –Same as Time.new. DateTime.parse(string) –Create DateTime from date stored in string

11. CIT 383: Administrative Scripting Date and Time Arithmetic Addition and substraction of constants –Increment by day (Date) or second (Time) –Decrement by day (Date) or second (Time) Subtraction of dates –Determine days between two Dates. –Determine seconds between two Times.

12. CIT 383: Administrative Scripting Ranges Sequence of values 1..10 ?a..?z Methods min max include?(num) Ranges as Intervals (1..10) === 4# true (1..10) === 99# false (1..10) === 2.718# true

13. CIT 383: Administrative Scripting Ranges and Arrays Ranges provide iterator methods –Including the each method. Ranges can be converted to Arrays –Use the to_a method. Ranges are stored efficiently –Only initial and final values are stored. –Do not convert 1..2**32 to an Array.

14. CIT 383: Administrative Scripting Date Ranges today = Date.today nextweek = today + 7 weekdates = today..nextweek weekdates.each do |date| puts date end

15. CIT 383: Administrative Scripting Waiting sleep(num) –Waits for num seconds. –Does not use any CPU during sleep. Applications –Wait before retrying an action that failed. –Periodic processes (check file every minute.)

16. CIT 383: Administrative ScriptingSlide #16 References 1.Michael Fitzgerald, Learning Ruby, O’Reilly, 2008. 2.David Flanagan and Yukihiro Matsumoto, The Ruby Programming Language, O’Reilly, 2008. 3.Hal Fulton, The Ruby Way, 2 nd edition, Addison-Wesley, 2007. 4.Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2 nd edition, Pragmatic Programmers, 2005.