Displays the contents of a file, a directory, a disk volume, a magnetic tape volume, or a CD-ROM volume in decimal, hexadecimal, octal format, ASCII, or formatted data structures.
This is frequently used when a file is not a simple text file where the content has a mixture of data types such as strings and integers.
What is the Unix/Linux command for this?
There's a few options.
od should be available on POSIX systems, so most Unix and Linux variants will have it. That command has a slew of options to control the output format.hexdump (from util-linux on my distro) is my favorite for a quick inspection (hexdump -C), but it's not available everywhere.xxd (installed with Vim) is great too - especially since it allows you to convert to a human-readable hex format, and to convert back to binary. So that gives you a pretty simple hex editor.