I have tried a couple of things

Please show what you have tried. You may be close and just need a little push. Include the code in <code>...</code> tags.

Update: You may wish to peruse Date to see if there is anything that would help.

Don't know if it's the "best" way, but I personally would use Date::Calc's Delta_Days function.

Look at Delta_Days and Delta_DHMS in the Date::Calc module. That should give you what you need.

use strict;
use warnings;
use feature qw( say );

use DateTime                   qw( );
use DateTime::Format::Strptime qw( );

my $format = DateTime::Format::Strptime->new(
   pattern   => '%d-%m-%Y',
   time_zone => 'local',
   on_error  => 'croak',
);

my $target = $format->parse_datetime('05-08-2012');
my $today = DateTime->today( time_zone => 'local' );

say $today->delta_days($target)->in_units('days');  # 123
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++

Most of the time, I find myself coming back to this module because it’s an abstract data type.   An instance of the object, once loaded with a particular date by whatever means, “is an” instance of that date.   It is completely opaque and it just does the right thing.   Since you often find yourself doing a series of not-quite trivial things with date/time values, this is a great tool.

I peeked at the source code once.   Wow.   “Glad somebody wrote that (and wrote it so well) ... glad it wasn’t me.”

Hey thanks man. Appreciate it.