ISO-8601

This. So much this.

In C:
#include <stdio.h>
#include <time.h>
#define SIZE 0x100
int main ()
{
    time_t t;
    char buffer[SIZE];
    struct tm ltime;
    t = time (0);
    localtime_r (& t, & ltime);
    strftime (buffer, SIZE, "%Y-%m-%d", & ltime);
    printf ("%s\n", buffer);
    return 0;
}

In Bourne-derived shell:
#!/bin/sh
iso8601=`date +%Y-%m-%d`
echo $iso8601


In Perl:
#!/usr/bin/perl
use POSIX qw/strftime/;
my $date = strftime "%Y-%m-%d", localtime;
print "$date\n";


In Ruby:
#!/usr/bin/ruby
iso8601 = Time.now.strftime("%Y-%m-%d")
p iso8601


In PHP:
<?php
$iso8601=date('Y-m-d'); 
print $iso8601."\n";


In Python:
#!/usr/bin/python
from datetime import date
iso8601=date.today().isoformat()
print iso8601

Got it? Good.