my ($date, $year) = /(\w+\s+\d+),?\s+(\d{4})/;
print "$date, $year\n";

##</code><code>##

use warnings;
use strict;

while (<DATA>){
    if (my ($date, $year) =
          /
          (         # start capture 1 ($date)
          \w+       # word characters (month)
          \s+       # space characters
          \d+       # date chars
          )         # end capture 1
          ,?        # comma or no comma, 
          \s+       # followed by possible whitespace
          (         # start capture 2 ($year)
          \d{4}     # four digits (year)
          )         # end capture 2
          /x
      )
      {
        print "$date, $year\n";
      }
}

__DATA__
For the fiscal year ended Dec 31, 2015xxx
For the fiscal year ending December 31 2015
For the fiscal year ending December 31, 2015 

##</code><code>##

Dec 31, 2015
December 31, 2015
December 31, 2015