HEX and ACSII convert with command line

Convert HEX to ASCII with command line and save into a file:

> echo 'd7b00402659ba2abd2cb0db27fa2b656' | xxd -r -p > 'common.key'

Convert ASCII to HEX with command line from a file:

> cat 'common.key' | od -A n -t x1 | sed 's/ *//g'