od

od is a command on various operating systems for displaying ("dumping") data in various human-readable output formats. The name is an acronym for "octal dump" since it defaults to printing in the octal data format.

Overview

The od program can display output in a variety of formats, including octal, hexadecimal, decimal, and ASCII. It is useful for visualizing data that is not in a human-readable format, like the executable code of a program, or where the primary form is ambiguous (e.g. some Latin, Greek and Cyrillic characters looking similar).

od is one of the earliest Unix programs, having appeared in version 1 AT&T Unix. It is also specified in the POSIX standards. The implementation for od used on Linux systems is usually provided by GNU Core Utilities.

Since it predates the Bourne shell, its existence causes an inconsistency in the do loop syntax. Other loops and logical blocks are opened by the name, and closed by the reversed name, e.g. if ... fi and case ... esac, but od's existence necessitates do ... done.

from https://en.wikipedia.org/wiki/Od_(Unix)