출처 : http://www.linuxinstead.com/blog/2009/04/21/using-vi-as-a-hex-editor/

Sometimes I find it useful to switch to hex mode when editing a file in vi. The command for switching is not very obvious so thought I’d share…

So, open a file in vi as usual, hit escape and type:
:%!xxd to switch into hex mode

And when your done hit escape again and type:
:%!xxd -r to exit from hex mode.

Okay, so this isn’t actaully switching to vi’s ‘hex mode’; vi doesn’t have one. What the above actually does is to stream vi’s buffer through the external program ‘xxd’.