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# Date and Time in Ruby

The Time class represents dates and times in Ruby. It is a thin layer over the system date and time functionality provided by the operating system. This class may be unable on your system to represent dates before 1970 or after 2038.

This tutorial will make you familiar with all the most wanted concepts of date and time.

## Getting Current Date and Time:

Following is the simple example to get current date and time:

    #!/usr/bin/ruby -w

    time1 = Time.new

    puts "Current Time : " + time1.inspect

    # Time.now is a synonym:
    time2 = Time.now
    puts "Current Time : " + time2.inspect

This will produce following result:

    Current Time : Mon Jun 02 12:02:39 -0700 2008
    Current Time : Mon Jun 02 12:02:39 -0700 2008

## Getting components of a Date & Time:

We can use Time object to get various components of date and time. Following is the example showing the same:

    #!/usr/bin/ruby -w

    time = Time.new

    # Components of a Time
    puts "Current Time : " + time.inspect
    puts time.year    # => Year of the date
    puts time.month   # => Month of the date (1 to 12)
    puts time.day     # => Day of the date (1 to 31 )
    puts time.wday    # => 0: Day of week: 0 is Sunday
    puts time.yday    # => 365: Day of year
    puts time.hour    # => 23: 24-hour clock
    puts time.min     # => 59
    puts time.sec     # => 59
    puts time.usec    # => 999999: microseconds
    puts time.zone    # => "UTC": timezone name

This will produce following result:

    Current Time : Mon Jun 02 12:03:08 -0700 2008
    2008
    6
    2
    1
    154
    12
    3
    8
    247476
    UTC

## Time.utc, Time.gm and Time.local Functions:

These two functions can be used to format date in standard format as follows:

    # July 8, 2008
    Time.local(2008, 7, 8)
    # July 8, 2008, 09:10am, local time
    Time.local(2008, 7, 8, 9, 10)
    # July 8, 2008, 09:10 UTC
    Time.utc(2008, 7, 8, 9, 10)
    # July 8, 2008, 09:10:11 GMT (same as UTC)
    Time.gm(2008, 7, 8, 9, 10, 11)

Following is the example to get all components in an array in the following format:

    [sec,min,hour,day,month,year,wday,yday,isdst,zone]

Try the following:

    #!/usr/bin/ruby -w

    time = Time.new

    values = t.to_a
    p values

This will generate following result:

    [26, 10, 12, 2, 6, 2008, 1, 154, false, "MST"]

This array could be passed to Time.utc or Time.local functions to get different format of dates as follows:

    #!/usr/bin/ruby -w

    time = Time.new

    values = t.to_a
    puts Time.utc(*values)

This will generate following result:

    Mon Jun 02 12:15:36 UTC 2008

Followin is the way to get time represented internally as seconds since the (platform-dependent) epoch:

    # Returns number of seconds since epoch
    time = Time.now.to_i

    # Convert number of seconds into Time object.
    Time.at(time)

    # Returns second since epoch which includes microseconds
    time = Time.now.to_f

## Timezones and daylight savings time:

You can use a Time object to get all the information related to Timezones and daylight savings as follows:

    time = Time.new

    # Here is the interpretation
    time.zone       # => "UTC": return the timezone
    time.utc_offset # => 0: UTC is 0 seconds offset from UTC
    time.zone       # => "PST" (or whatever your timezone is)
    time.isdst      # => false: If UTC does not have DST.
    time.utc?       # => true: if t is in UTC time zone
    time.localtime  # Convert to local timezone.
    time.gmtime     # Convert back to UTC.
    time.getlocal   # Return a new Time object in local zone
    time.getutc     # Return a new Time object in UTC

## Formatting Times and Dates:

There are various ways to format date and time. Here is one example showing few:

    #!/usr/bin/ruby -w
    time = Time.new

    puts time.to_s
    puts time.ctime
    puts time.localtime
    puts time.strftime("%Y-%m-%d %H:%M:%S")

This will produce following result:

    Mon Jun 02 12:35:19 -0700 2008
    Mon Jun  2 12:35:19 2008
    Mon Jun 02 12:35:19 -0700 2008
    2008-06-02 12:35:19

## Time Formatting Directives:

These directives in the following table are used with the method Time.strftime.

Directive | Description
--- | ---
%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.
%d | Day of the month (01 to 31).
%H | Hour of the day, 24-hour clock (00 to 23).
%I | Hour of the day, 12-hour clock (01 to 12).
%j | Day of the year (001 to 366).
%m | Month of the year (01 to 12).
%M | Minute of the hour (00 to 59).
%p | Meridian indicator (AM or PM).
%S | Second of the minute (00 to 60).
%U | Week number of the current year, starting with the first Sunday as the first day of the first week (00 to 53).
%W | Week number of the current year, starting with the first Monday as the first day of the first week (00 to 53).
%w | Day of the week (Sunday is 0, 0 to 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 to 99).
%Y | Year with century.
%Z | Time zone name.
%% | Literal % character.

## Time arithmetic:

You can do simple arithmetic with time as follows:

    now = Time.now     # Current time
    past = now - 10    # 10 seconds ago. Time - number => Time
    future = now + 10  # 10 seconds from now Time + number => Time
    future - now       # => 10  Time - Time => number of seconds

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