# Always use gmtime and timegm when
# dealing with dates without times.

use Time::Local qw( timegm );

# Replace with your input.
my $then_date_str = 'YYYYMMDD';

my $then_date = do {
   my ($y, $m, $d) = $then_date_str =~ /^(.{4})(.{2})(.{2})\z/;
   $m--;
   timegm(0, 0, 0, $d, $m, $y)
};

my $now_date = do {
   my ($y, $m, $d) = (localtime())[5,4,3];
   timegm(0, 0, 0, $d, $m, $y)
};

my $diff = $now_date - $then_date;
my $diff_days = int($diff / (24*60*60));

if    ($diff_days <  -1) { printf("%d days ago\n", -$diff_days); }
elsif ($diff_days == -1) { print("yesterday\n"); }
elsif ($diff_days ==  1) { print("tomorrow\n"); }
elsif ($diff_days >   1) { printf("%d days from now\n", $diff_days); }
else                     { print("today\n"); }