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3.5. Difference of Two Dates
3.5.1. Problem
You need to find the number of days
between two dates or times.
3.5.2. Solution
If your dates are in Epoch seconds and fall in the range Fri
Dec 13 20:45:52 1901 to Tue Jan 19 03:14:07
2038 (inclusive), subtract one from the other and convert
the seconds to days:
$seconds = $recent - $earlier;
If you have distinct DMYMHS values or are worried about the range
limitations of Epoch seconds, use the Date::Calc module from CPAN. It
can calculate the difference between dates:
use Date::Calc qw(Delta_Days);
$days = Delta_Days( $year1, $month1, $day1, $year2, $month2, $day2);
It also calculates the difference between a pair of dates and times:
use Date::Calc qw(Delta_DHMS);
($days, $hours, $minutes, $seconds) =
Delta_DHMS( $year1, $month1, $day1, $hour1, $minute1, $seconds1, # earlier
$year2, $month2, $day2, $hour2, $minute2, $seconds2); # later
3.5.3. Discussion
One problem with Epoch seconds is how to convert the large integers
back to forms that people can read. The following example shows one
way of converting an Epoch seconds value back to its component
numbers of weeks, days, hours, minutes, and seconds:
$bree = 361535725; # 16 Jun 1981, 4:35:25
$nat = 96201950; # 18 Jan 1973, 3:45:50
$difference = $bree - $nat;
print "There were $difference seconds between Nat and Bree\n";
There were 265333775 seconds between Nat and Bree
$seconds = $difference % 60;
$difference = ($difference - $seconds) / 60;
$minutes = $difference % 60;
$difference = ($difference - $minutes) / 60;
$hours = $difference % 24;
$difference = ($difference - $hours) / 24;
$days = $difference % 7;
$weeks = ($difference - $days) / 7;
print "($weeks weeks, $days days, $hours:$minutes:$seconds)\n";
(438 weeks, 4 days, 23:49:35)
Date::Calc''s
functions can ease these calculations. The
Delta_Days function returns the number of days
between two dates. It takes the two dates as a list: year, month,
day. The dates are given chronologically—earliest first.
use Date::Calc qw(Delta_Days);
@bree = (1981, 6, 16); # 16 Jun 1981
@nat = (1973, 1, 18); # 18 Jan 1973
$difference = Delta_Days(@nat, @bree);
print "There were $difference days between Nat and Bree\n";
There were 3071 days between Nat and Bree
The
Delta_DHMS function returns a four-element list
corresponding to the number of days, hours, minutes, and seconds
between the two dates you give it.
use Date::Calc qw(Delta_DHMS);
@bree = (1981, 6, 16, 4, 35, 25); # 16 Jun 1981, 4:35:25
@nat = (1973, 1, 18, 3, 45, 50); # 18 Jan 1973, 3:45:50
@diff = Delta_DHMS(@nat, @bree);
print "Bree came $diff[0] days, $diff[1]:$diff[2]:$diff[3] after Nat\n";
Bree came 3071 days, 0:49:35 after Nat
3.5.4. See Also
The documentation for the CPAN module Date::Calc
