generate macOS app icons

generate_icns.sh

#!/usr/bin/env bash
#
# convert big png to macOS app icon sets
#

set -o errexit
set -o pipefail
set -o nounset

trap 'echo "Ctrl-C captured and exit."; exit 1' INT
trap 'echo "some error occured at $(pwd) and exit."; exit 8' SIGHUP

original_png="$1"

if [ ! -r "$original_png" ]; then
    echo "$original_png is not readable"
    exit 1
fi

mkdir -p Icon.iconset
rm -rf -- Icon.iconset/*

sips -z 16 16     "$original_png" --out Icon.iconset/icon_16x16.png
sips -z 32 32     "$original_png" --out Icon.iconset/icon_16x16@2x.png
sips -z 32 32     "$original_png" --out Icon.iconset/icon_32x32.png
sips -z 64 64     "$original_png" --out Icon.iconset/icon_32x32@2x.png
sips -z 128 128   "$original_png" --out Icon.iconset/icon_128x128.png
sips -z 256 256   "$original_png" --out Icon.iconset/icon_128x128@2x.png
sips -z 256 256   "$original_png" --out Icon.iconset/icon_256x256.png
sips -z 512 512   "$original_png" --out Icon.iconset/icon_256x256@2x.png
sips -z 512 512   "$original_png" --out Icon.iconset/icon_512x512.png
sips -z 1024 1024 "$original_png" --out Icon.iconset/icon_512x512@2x.png

rm -f Icon.icns
iconutil -c icns Icon.iconset