Od and Hexdump
On Unix/POSIX/GNU systems: "The utilities od and hexdump output octal, hex, or otherwise encoded bytes from a file or stream... Depending on your system type, either or both of these two utilities will be available--BSD systems deprecate od for hexdump, GNU systems the reverse. The two utilities, however, have exactly the same purpose, just slightly different switches."
Read more about this topic: Hex Dump