Create icns Icon File from 1024px PNG Master

create-icns.sh

# An easy way to create .icns files
# Inspired by http://stackoverflow.com/a/20703594

function mkicns() {
    if [[ -z "$@" ]]; then
        echo "Input file missing"
    else
        filename=${1%.*}
        mkdir $filename.iconset
        sips -z 16 16   $1 --out $filename.iconset/icon_16x16.png
        sips -z 32 32   $1 --out $filename.iconset/icon_16x16@2x.png
        sips -z 32 32   $1 --out $filename.iconset/icon_32x32.png
        sips -z 64 64   $1 --out $filename.iconset/icon_32x32@2x.png
        sips -z 128 128 $1 --out $filename.iconset/icon_128x128.png
        sips -z 256 256 $1 --out $filename.iconset/icon_128x128@2x.png
        sips -z 256 256 $1 --out $filename.iconset/icon_256x256.png
        sips -z 512 512 $1 --out $filename.iconset/icon_256x256@2x.png
        sips -z 512 512 $1 --out $filename.iconset/icon_512x512.png
        cp $1 $filename.iconset/icon_512x512@2x.png
        iconutil -c icns $filename.iconset
        rm -r $filename.iconset
    fi
}

Brilliant! Thanks!