gntp-send software package provides Command line application to send growl message with GNTP, 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 gntp-send
gntp-send is installed in your system.
Make ensure the gntp-send package were installed using the commands given below,
$ sudo dpkg-query -l | grep gntp-send *
You will get with gntp-send package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Network |
| Package | gntp-send |
| Version | 0.3.4-1 |
| Description | Command line application to send growl message with GNTP |
| Sub Section | Net |