A script to create icns file on MacOS for inclusion in a program you'll need an original file at 1024px
and of course MacOS
either put the script in your path or in the directory you want to work in
if in the path just run mkiconset.sh and answer two questions
if in the target directory then run ./mkiconset.sh
You should see the following prompts
Supply iconset name:MYICON
Starting ICON (should be 1024 in size):ICON.png
The script will create a directory with the iconset name above eg. MYICON.iconset
Then the script will create a file with the name eg. MYICON.icns
That's it easy peasy