epoch_julian_gregorian_date.pl

#!/usr/bin/perl -w

# Without parameters, the script displays the current date in three different
# formats (epoch, julian, and gregorian).  Here is a example run:
#
#   $ ./complicated_date.pl
#   epoch:     1471012564  Fri Aug 12 10:36:04 2016
#   julian:    2457613.10837963
#   gregorian: 1471012564  Fri Aug 12 10:36:03 2016
#
# You can also supply an epoch time (seconds since 1970) and the script will
# display the three different formats for that particular point in time.

use strict;

sub display_date (@)
{
    my $now_time = shift @_;
    my $julian = shift @_;
    my $newline = shift @_;

    my $now_date = localtime($now_time);
    my $greg_time = ($julian - 2440587.5) * 86400;
    my $greg_round = int($greg_time + $greg_time/abs($greg_time*2));
    my $greg_date = localtime($greg_time);

    print "\n" if $newline;
    print "epoch:     $now_time  $now_date\n";
    print "julian:    $julian\n";
    print "gregorian: $greg_round  $greg_date\n";
}

if (@ARGV > 0) {
    my $newline = 0;
    foreach my $arg (@ARGV) {
        my ($now_time, $julian) = (0, 0);

        if (length($arg) >= 9 && $arg =~ /^\d+$/) {
            $now_time = $arg;
            $julian = ($now_time / 86400) + 2440587.5;
        }

        if (length($arg) < 9 || $arg =~ /\./) {
            $julian = $arg;
            $now_time = ($julian - 2440587.5) * 86400;
        }

        display_date($now_time, $julian, $newline);
        $newline = 1;
    }
} else {
    my $now_time = time();
    my $julian = ($now_time / 86400) + 2440587.5;
    display_date($now_time, $julian, 0);
}