od (Octal Dump) is a standard Unix command line utility. It shows a byte per byte representation of any file.
Is useful at least in two contexts, when you want to see what's
inside a binary data file (to reverse engineering it, let's say) and when you want to know exactly which
ASCII byte codes are written on a text file.
The GNU implementation was written by Jim Meyering and as usual
with GNU programs it has a enormous number of argument options.
In its default mode it prints 16 bytes of the file per line, in 8
octal numbers coding two bytes of input each, with the file offset of the
input at the beginning of each output line.
You can change the base of the output (octal, hexadecimal, decimal,
backslashed escaped non-printable ASCII characters,...), and the
representation of the data (bytes, shorts, longs...).