Install

apt-get install hexedit

Hotkey

F1: Help

Ctrl-L: redraw

Return: go to

Backspace: undo previous character

F2:     save             * without comfirm !!

Ctrl-X / F10: save and exit

Ctrl-C: exit without saving

Tab:    toggle hex/ascii

Ctrl-S: search forward

Ctrl-R: search backward

Cut&Paste

       F9 - set mark
       F7 - copy selected region
       F8 - paste (yank) previously copied region.
       F11 - save previously copied region to a file.
       F12 - fill the selection with a string

Esc+T - truncate the file at the current location

Task 1: 縮 size

3 bytes -> 2 bytes

Task 2:

2 bytes => 512 bytes