See Date::Manip and its DateCalc() method.

Date::Manip is excellent for certain things like natural string parsing but otherwise it's not the best choice. DateTime is amazing and handles time zones, ranges, date math, and such really well but it has bit of a learning curve and it's a little slow. Date::Calc is very fast but its functions are generally low level so your code will be more verbose. There are some other date packages but they offer nothing over DateTime and Date::Calc.

Prefer DateTime if you want a wealth of date operational power. Prefer Date::Calc if you have a need for speed.

Update: been years but I want to amend it—Time::Piece has something to offer in comparison to the others: it’s core (since v5.9.5).

I need to do the time difference as $date2-$date1

I'll assume you need the difference in seconds. If you need minutes or hours, divide by 60 or by 60/60.

I've used Date::Calc for a long time with fine results. There are several functions (as well as an OOP interface for the same functions) available, depending on what you need. You'll have to do a little parsing, but then you turn the string into the seconds since the epoch (doesn't matter which one) and just subtract one from the other.

use strict;
use warnings;
use Date::Calc qw(Mktime); # Turns a date string into seconds since ep
+och

my $dt_str2="31/12/2009 6:29:26 p.m.";
my $dt_str1="31/12/2009 6:14:25 p.m.";

my ($day, $mo, $yr, $hr, $min, $sec, $mer) = 
   $dt_str1 =~ m{(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+) ([ap])};
$hr += 12 if $mer eq 'p';
die "Problem with date string $_" if $hr > 23;
          # Note element order for Date::Calc functions!
my $dt1 = Mktime($yr, $mo, $day, $hr, $min, $sec);

($day, $mo, $yr, $hr, $min, $sec, $mer) = 
   $dt_str2 =~ m{(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+) ([ap])};
$hr += 12 if $mer eq 'p';
die "Problem with date string $_" if $hr > 23;
my $dt2 = Mktime($yr, $mo, $day, $hr, $min, $sec);

print $dt2 - $dt1, "\n";
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Or you could make it into a loop if you had a lot of these to parse at once (and it's cleaner looking too).

use strict;
use warnings;
use Date::Calc qw(Mktime); # Turns a date string into seconds since ep
+och

my $dt_str2="31/12/2009 6:29:26 p.m.";
my $dt_str1="31/12/2009 6:14:25 p.m.";

my @dates_to_compare;
for ($dt_str1, $dt_str2) {
    my ($day, $mo, $yr, $hr, $min, $sec, $mer) = 
       m{(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+) ([ap])};
    $hr += 12 if $mer eq 'p';
    die "Problem with date string $_" if $hr > 23;
                            # Note element order for Date::Calc functi
+ons!
    push @dates_to_compare, Mktime($yr, $mo, $day, $hr, $min, $sec);
}
# using pop clears out the array, which is helpful when looping
print pop(@dates_to_compare) - pop(@dates_to_compare), "\n";
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I hope this helps