#!/usr/bin/perl
use warnings;
use strict;
use POSIX qw(strftime);

my $calc_days;

if ( ! @ARGV ) {
   print "Please enter number of days (+/-): ";

   $calc_days = <STDIN>;
   chomp $calc_days;
   exit 1 if $calc_days eq '';
}
else {
   $calc_days = $ARGV[0];
}

# Convert days to seconds;
my $secs = $calc_days * 24 * 60 * 60;

# Convert seconds to a readable format, adding them to the current time
my $final_date = strftime ('%d/%m/%Y %T', localtime(time() + $secs));

print "$final_date\n";