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Date/Time

Another very handy and widely used object is Time, which contains date and time. It depends on operating system how this object is represented: in Unix, as you probably know well, the time is the number of seconds since 1st of January 1970. Using Ruby you do not have to worry about the dates before 1970 (they are represented by the negative integer) and after 2038.
To get the current time, use Time.now class method. You can add and substract the seconds from the time object to represent future or past:

time = Time.now
#=> 2014-06-13 21:05:19 +0200  # the default representation of time, date + time + timezone

time + 60                  # one minute later
#=> 2014-06-13 21:06:19 +0200

time - 60*60*24*365 * 50   # fifty years before (well, not exactly, because not every year is 365 days long)
#=> 1964-06-25 20:05:19 +0100


Date/Time Formatting

Default representatation of time is quite readable for humans, but sometimes you need another formatting. To format date/time with user-defined pattern, use strftime method with specified pattern, where %Y means year, %m - month, %d - day, etc. You can find exact description of the time pattern in the documentation ri Time.strftime. To extract the parts of the date/time use time.year, time.month or time.day instance methods. Finally, to convert date/time to Unix representation - the number of seconds - use to_i.
Notice that you must load additional library by require 'time' to use some methods described above.

require 'time'                 # load additional date/time helper methods
#=> true

time.year                      # returns integer with year
#=> 2014

time.iso8601                   # converts date/time to string according to iso-8601 standard
#=> "2014-06-13T21:05:19+02:00"

time.httpdate                  # httpdate represents the date/time in format used by http protocol
#=> "Fri, 13 Jun 2014 19:05:19 GMT"

time.strftime('Today is %A, %B %e, %l:%M:%S %p and %3N miliseconds')
#=> "Today is Friday, June 13,  9:05:19 PM and 775 miliseconds"

time.to_i                      # Unix number of seconds since the Big Bang
#=> 1402686319


Creating Date/Time Object

To create a new date/time instance with specified time, use constructor Time.new with year, month, day, hour, minute and second as arguments. You can ommit some parts, for example give only year, month and date, like Time.new(2014, 6, 13). You can also convert the Unix number of seconds to date/time object, using Time.at class method.

Time.new(2014, 6, 13)      # just the date, do not care about time
#=> 2014-06-13 00:00:00 +0200

Time.new(2014, 6, 13, 22)  # the same date at 22:00:00
#=> 2014-06-13 22:00:00 +0200

Time.at(1402686319)        # today
#=> 2014-06-13 21:05:19 +0200

Time.at(0)                 # at the beginning of epoch
#=> 1970-01-01 01:00:00 +0100


Parsing Date/Time from the String

It is very common in Sysadmin work to parse some logs and get the date and time from there. In Ruby there is a sophisticated class method Time.parse to parse a given string and return date/time object. It is raising an exception when it cannot pare it properly.

require 'time'                              # load time helper methods
#=> true

Time.parse('2014-06-13')                    # simple to parse
#=> 2014-06-13 00:00:00 +0200

Time.parse('2014-06-13 22:13')              # with given hour and minutes
#=> 2014-06-13 22:13:00 +0200

Time.parse('12:00')                         # when only time give, default date is today
#=> 2014-06-13 12:00:00 +0200

Time.parse('Friday, June 13, 22:13:13')     # more sophisticated parsing
#=> 2014-06-13 22:13:13 +0200

Time.parse("Fri, 13 Jun 2014 19:05:19 GMT") # http protocol standard
#=> 2014-06-13 21:05:19 +0200

Time.parse("Captain's log, stardate 41153.7. Our destination is planet Deneb IV...")
#=> 2014-06-13 04:11:53 +0200                   # but it is not parsing non-standard time correctly...