title: `date` command on OS X doesn't have ISO 8601 `-I` option?
body: <p>In a Bash script, I want to print the current datetime in <a href="http://en.wikipedia.org/wiki/ISO_8601" rel="noreferrer">ISO 8601</a> format (preferably UTC), and it seems that this should be as simple as <code>date -I</code>:</p>
  
  <p><a href="http://ss64.com/bash/date.html" rel="noreferrer">http://ss64.com/bash/date.html</a></p>
  
  <p>But this doesn't seem to work on my Mac:</p>
  
  <pre><code>$ date -I
  date: illegal option -- I
  usage: date [-jnu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
              [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
  </code></pre>
  
  <p>And indeed, <code>man date</code> doesn't list this option.</p>
  
  <p>Anyone know why this is, or any other (easy) way for me to print the date in ISO 8601 format? Thanks!</p>