How to convert a text file to binary file using linux commands

Question

I have hex code of a binary in text (string) format. How do I convert it to a binary file using linux commands like cat and echo ?

I know command following command with create a binary test.bin. But what if this hexcode is in another .txt file ? How do I "cat" the content of text file to "echo" and generate a binary file ?

# echo -e "\x00\x001" > test.bin

Answer 1

use xxd -r. it reverts a hexdump to its binary representation.

source and source

Edit: The -p parameter is also very useful. It accepts "plain" hexadecimal values, but ignores whitespace and line changes.

So, if you have a plain text dump like this:

echo "0000 4865 6c6c 6f20 776f 726c 6421 0000" > text_dump

You can convert it to binary with:

xxd -r -p text_dump > binary_dump

And then get useful output with something like:

xxd binary_dump