How to convert hex to ASCII characters in the Linux shell?

echo -n 5a | perl -pe 's/([0-9a-f]{2})/chr hex $1/gie'

Note that this won't skip non-hex characters. If you want just the hex (no whitespace from the original string etc):

echo 5a | perl -ne 's/([0-9a-f]{2})/print chr hex $1/gie'

Also, zsh and bash support this natively in echo:

echo -e '\x5a'

You can do this with echo only, without the other stuff. Don't forget to add "-n" or you will get a linebreak automatically:

echo -n -e "\x5a"

I used to do this with xxd:

echo -n 5a | xxd -r -p

But then I realised that in Debian/Ubuntu, xxd is part of vim-common and hence might not be present in a minimal system. To also avoid Perl (IMHO also not part of a minimal system), I ended up using sed, xargs, and printf like this:

echo -n 5a | sed 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf

Mostly, I only want to convert a few bytes and it's okay for such tasks. The advantage of this solution over the one of ghostdog74 is, that this can convert hex strings of arbitrary lengths automatically. xargs is used because printf doesnt read from standard input.