date calculations #perl #dates #snippet

dcalc.pl

#!/usr/bin/env perl

use strict;
use FindBin;
use DateTime;
use DateTime::Duration;
use Getopt::Long;

my ($days, $date);
GetOptions(
    "days:i" => \$days,
    "date:s" => \$date
);

if(  ! ($days || $date) ) {
    die <<EOF;
Usage: $FindBin::Script [--days n | --date d]
    --days n  if n<0, date n days ago; if n>0, date n days from now
    --date d  days between now and date d
EOF
}

my $right_now = DateTime->now(time_zone => "America/New_York");
my $now = DateTime->new(
                year => $right_now->year, month => $right_now->month, day => $right_now->day,
                hour => 0, minute => 0, second => 0,
                time_zone => "America/New_York");
my $fmt = "%8s : %s\n";
if( defined $days ) {
    my $then = $now + DateTime::Duration->new( days => $days );
    &display($now->ymd, $then->ymd, $days);
} elsif( defined $date) {
    if( $date =~ /^(\d\d\d\d)-(\d\d)-(\d\d)$/ ) {
        my $then = DateTime->new(time_zone => "America/New_York",
                    year => $1, month => $2, day => $3,
                    hour => 0, minute => 0, second => 0);
        my $dur;
        my $delta_sec = $then->epoch - $now->epoch;
        my $is_past = ($delta_sec < 0 ? -1 : 1);
        my $days = sprintf("%d", abs($delta_sec/3600/24));
        &display($now->ymd, $then->ymd, $days*$is_past);
    } else {
        die "Date format must be yyyy-MM-DD\n";
    }
}


sub display {
    my ($now, $then, $duration) = @_;
    printf $fmt, "Today", $now;
    printf $fmt, "Then",  $then;
    if( $duration > 0 ) {
        $duration .= " days from now";
    } elsif( $duration < 0 ) {
        $duration = abs($duration) . " days ago";
    }
    printf $fmt, "Duration", $duration;
}