In addition to checking Config as suggested by grep, you can use a solution provided by perlport. To quote:

If you need to distinguish between endian architectures you could use either of the variables set like so:

  $is_big_endian   = unpack("h*", pack("s", 1)) =~ /01/;
  $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;
[download]