Perl script: dt

dt can be used for simple date arithmetic in a shell.

Without arguments, it prints the current date:

$dt 2017-02-07 (Tu)

If the argument is a number, it is interpreted as days. It will print the date in that many days:

$dt 5 2017-02-12 (So)

The argument can be suffixed with w in which case the argument is interpreted as weeks;

$dt 1w 2017-02-21 (Tu)

dt - the script

#!/usr/bin/perl
use warnings;
use strict;
use Getopt::Long;

use feature 'say';

GetOptions(
    'help' => \my $help
);

if ($help) {

  print "
  dt           Print today's date
  dt 5         Print date in five days
  dt 7w        Print date in seven weeks

";
  exit 0;
}

unless (@ARGV) {

  print_date(time);
  exit 0;
}

my $days_or_weeks = shift;

my $secs_per_day = 24*60*60;
if ($days_or_weeks =~ s/w//) {
  print_date(time + $secs_per_day * $days_or_weeks * 7); 
}
else {
  print_date(time + $secs_per_day * $days_or_weeks); 
}

sub year_month_day_weekday {

  my $time = shift;

  my ($second, $minute, $hour, $day_of_month, $month, $year, $day_of_week, $day_of_year, $daylight_saving_time) = localtime($time);
  
  $month ++;
  $year  += 1900;
  $month        = sprintf("%02d", $month       );
  $day_of_month = sprintf("%02d", $day_of_month);

  return ($year, $month, $day_of_month, ('So', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa')[$day_of_week]);

}
sub print_date {

  my $time = shift;
  my @ymdw = year_month_day_weekday($time);

  say "$ymdw[0]-$ymdw[1]-$ymdw[2] ($ymdw[3])";
}

Github repository scripts-and-utilities, path: /dt

Perl script: dt

dt - the script

See also