This is from man hexdump:

The hexdump utility is a filter which displays the specified files, or the standard input, if no files are specified, in a user specified format.

In short, it transforms text from one format to another. Traditionally, hexdump is mostly used for debugging, especially programs that are using low-level libraries.

But now with unicode, I sometimes use it to get different values of characters or to transform lines or files.

Because it is a filter, you send text into it. An easy way to do this is with the pipe operator (|).

It outputs the text displayed as either ASCII, decimal, hex, or octal. You use format specifiers to determine the output. These are command options you put after the hexdump.

If you want to see the results on the command line you need to start off with echo.

So it's echo text-to-transform | hexdump options optional-format-specifiers

An example from the man page is:

echo hello | hexdump -v -e '/1 "%02X\n"'

which outputs the hex value of each letter.

This example may not seem useful but remember it's possible to recode entire files or dump contents of memory in a human readable form.

If you don't send input to hexdump, it keeps waiting and appears to do nothing. This is what would happen if you ran hexdump by itself. When you say it froze, did more than that happen?

hexdump -C does what you want.

# hexdump -C /etc/passwd
00000000  72 6f 6f 74 3a 78 3a 30  3a 30 3a 72 6f 6f 74 3a  |root:x:0:0:root:|
00000010  2f 72 6f 6f 74 3a 2f 62  69 6e 2f 62 61 73 68 0a  |/root:/bin/bash.|
00000020  64 61 65 6d 6f 6e 3a 78  3a 31 3a 31 3a 64 61 65  |daemon:x:1:1:dae|
00000030  6d 6f 6e 3a 2f 75 73 72  2f 73 62 69 6e 3a 2f 62  |mon:/usr/sbin:/b|
00000040  69 6e 2f 73 68 0a 62 69  6e 3a 78 3a 32 3a 32 3a  |in/sh.bin:x:2:2:|
00000050  62 69 6e 3a 2f 62 69 6e  3a 2f 62 69 6e 2f 73 68  |bin:/bin:/bin/sh|
...