How can I calculate the number of days between two dates in Perl?

Question

Heylo,

I want to calculate (using the default Perl installation only) the number of days between two dates. The format of both the dates are like so 04-MAY-09. (DD-MMM-YY)

I couldn't find any tutorials that discussed that date format. Should I be building a custom date checker for this format? Further reading of the Date::Calc on CPAN it looks unlikely that this format is supported.

Thanks.

Answer 1

You could convert the dates into the long integer format, which is the number of seconds since the epoch (some date in 1970 I think). You then have two variables that are the dates in seconds; subtract the smaller from the larger. Now you have a time span in seconds; divide it by the number of seconds in 24 hours.

Answer 2

Time::ParseDate will handle that format just fine:

use Time::ParseDate qw(parsedate);

$d1="04-MAR-09";
$d2="06-MAR-09";

printf "%d days difference\n", (parsedate($d2) - parsedate($d1)) / (60 * 60 * 24);

Answer 3

Date::Calc has Decode_Date_EU (and US etc)

#!/usr/bin/perl
use Date::Calc qw(Delta_Days Decode_Date_EU);

($year1,$month1,$day1) = Decode_Date_EU('02-MAY-09');
($year2,$month2,$day2) = Decode_Date_EU('04-MAY-09');

print "Diff = " . Delta_Days($year1,$month1,$day1, $year2,$month2,$day2);

Answer 4

Convert the two dates to seconds and then do the math:

#!/usr/bin/perl

use strict;
use warnings;
use POSIX qw/mktime/;

{

    my %mon = (
     JAN => 0,
     FEB => 1,
     MAR => 2,
     APR => 3,
     MAY => 4,
     JUN => 5,
     JUL => 6,
     AUG => 7,
     SEP => 8,
     OCT => 9,
     NOV => 10,
     DEC => 11,
    );

    sub date_to_seconds {
     my $date = shift;
     my ($day, $month, $year) = split /-/, $date;

     $month = $mon{$month};
     if ($year < 50) { #or whatever your cutoff is
      $year += 100; #make it 20??
     }

     #return midnight on the day in question in 
     #seconds since the epoch
     return mktime 0, 0, 0, $day, $month, $year;
    }
}

my $d1 = "04-MAY-99";
my $d2 = "04-MAY-00";

my $s1 = date_to_seconds $d1;
my $s2 = date_to_seconds $d2;

my $days = int(($s2 - $s1)/(24*60*60));

print "there are $days days between $d1 and $d2\n";

Answer 5

If you care about accuracy, keep in mind that not all days have 86400 seconds. Any solution based on that assumption will not be correct for some cases.

Here's a snippet I keep around to calculate and display date/time differences a few different ways using the DateTime library. The last answer printed is the one you want, I think.

#!/usr/bin/perl -w

use strict;

use DateTime;
use DateTime::Format::Duration;

# XXX: Create your two dates here
my $d1 = DateTime->new(...);
my $d2 = DateTime->new(...);

my $dur = $d1 > $d2 ? ($d1 - $d2) : ($d2 - $d1);

my $dur_abs = $d1 > $d2 ? 
  $d1->subtract_datetime_absolute($d2) :
  $d2->subtract_datetime_absolute($d1);

my $fmt = DateTime::Format::Duration->new(pattern => 
  '%Y years, %m months, %e days, %H hours, %M minutes, %S seconds');

print $fmt->format_duration($dur), "\n";

$dur = $d1->delta_md($d2);

my $dy = int($dur->delta_months / 12);
my $dm = $dur->delta_months % 12;
print "$dy years $dm months ", $dur->delta_days, " days\n";
print $dur->delta_months, " months ", $dur->delta_days, " days\n";
print $d1->delta_days($d2)->delta_days, " days\n";