Use the Config module and $Config{byteorder}.

Straight from module docs:

byteorder

From byteorder.U:


This variable holds the byte order. In the following, larger digits
indicate more significance. The variable byteorder is either 4321 on a
big-endian machine, or 1234 on a little-endian, or 87654321 on a Cray 
+...
or 3412 with weird order !
[download]

BTW doing a search of determine endian yeilded several results.

search is your friend

grep

grep> cd pub grep> more beer