Here is a way to get the difference between the dates in days from an array of dates. (Note that the dates are sorted. If your array isn't sorted you would have some negative differences).

#!/usr/bin/perl
use strict;
use warnings;
use Time::Piece;


my @date = (
    '2014-06-01',
    '2014-06-02',
    '2014-06-03',
    '2014-06-04'
);

for my $i (0 .. $#date-1) {
    my $d1 = Time::Piece->strptime($date[$i], '%Y-%m-%d');
    for my $j ($i+1 .. $#date) {
        my $d2 = Time::Piece->strptime($date[$j], '%Y-%m-%d');
        my $diff = $d2 - $d1;
        print $d1->ymd, " and ", $d2->ymd, " is ", $diff->days, "\n";
    }    
}
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Prints

2014-06-01 and 2014-06-02 is 1
2014-06-01 and 2014-06-03 is 2
2014-06-01 and 2014-06-04 is 3
2014-06-02 and 2014-06-03 is 1
2014-06-02 and 2014-06-04 is 2
2014-06-03 and 2014-06-04 is 1
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