dhex software package provides ncurses based hex editor with diff mode, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install dhex
dhex is installed in your system.
Make ensure the dhex package were installed using the commands given below,
$ sudo dpkg-query -l | grep dhex *
You will get with dhex package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Editors |
| Package | dhex |
| Version | 0.68-2+b1 |
| Description | ncurses based hex editor with diff mode |
| Sub Section | Editors |