Make a macOS app icon from an image

macOS has everything you need to make an icon file for your application from the terminal.

macOS application icons are really a bundle ("iconset") of images at various sizes (16×16, 32×32, 64×64, ..., 1024×1024).

First create a myicon.iconset directory containing your icon image at all the sizes needed using the sips command line tool:

sips -Z 16 myicon.png --out myicon/icon_16x16.png
sips -Z 32 myicon.png --out myicon/icon_16x16@2x.png
sips -Z 32 myicon.png --out myicon/icon_32x32.png
sips -Z 64 myicon.png --out myicon/icon_32x32@2x.png
...

Then bundle them together with the iconutil command:

iconutil -c icns myicon.iconset

Here is a Makefile to do this automatically. Just save the Makefile to a directory containing your icon image file; change the variables NAME and ICON at the top; type make in the Terminal, and you're done: https://gist.github.com/eliteraspberries/a536f28b0498ec844fb210bb597738e2