TL;DR

Use this shell script on macOS to generate all the icon size combinations you need to publish your app to the iTunes and Google Play stores.

How To

Run mkicons.sh to display usage instructions:

VERSION: 1.0.0
USAGE:
    ./mkicons.sh file destination

DESCRIPTION:
    Generate a complete set of iOS application icons.

    file - The source png image. Preferably above 1024x1024
    destination - The destination path where the icons are output to.

    This script is depend on sips, a small command line utility available on
    macOS.
AUTHOR:
    Jason <jason.leach@fullboar.ca>

LICENSE:
    Apache 2.0

EXAMPLE:
    ./mkicons.sh 1024.png ~/out

How it Works

This script uses sips, a built in image process utility on macOS to resize the input image to all the options you need. See the code for exact params.