#!/usr/bin/perl

 use v5.10;  # (OP's code, verbatim)
 use strict;
 use warnings;
 
 use Data::Dumper;
 use DateTime::Format::Strptime;
 use Time::Piece;
 
 $Data::Dumper::Sortkeys = 1;
 
 my $date = '05/10/1969';
 my $ymd = '%Y-%m-%d';
 my $mdy = '%m/%d/%Y';
 
 my $t = Time::Piece->strptime($date,$mdy);
 
 say $t->ymd; # Prints as normal
 say $t->strftime($ymd); # Segmentation fault