* This one time, at band camp, George Vieira said:
> Hi all,
>
> Is there a way to subtract the number of days remaining from a date so I can
> report back "125 days remaining" etc.. under linux/perl?
>
> I want to subtract it from a date which will be a special event etc..
> Is there a date to interger conversion or something?
>
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), simply 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, $day2);
It also calculates the difference between dates and times:
use Date::Calc qw(Delta_DHMS);
($days, $hours, $minutes, $seconds) =
Delta_DHMS( $year1, $month1, $day1, $hour1, $minute1, $seconds1, # earlier
$year2, $month2, $day2, $hour2, $minute2, $seconds2); # later
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
See Also
The documentation for the CPAN module Date::Calc
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