Takes an icon PNG as an argument, uses sips (macOS) or convert (ImageMagick), makes a lot of icons!

apple-app-icons.sh

#!/bin/bash

# Takes an icon PNG as an argument, uses sips (macOS) or convert (ImageMagick), makes a lot of icons!
input_file=$1
sizes=(20 29 40 50 57 60 72 76 83.5 512)
scales=(1 2 3)

for size in "${sizes[@]}"
do
    for scale in "${scales[@]}"
    do
        output_size=$(echo "${size}*${scale}" | bc -l)
        output_file="$(dirname "$input_file")/${size}@${scale}x.png"
        if command -v sips >/dev/null 2>&1; then
            sips --resampleWidth ${output_size} "${input_file}" --out $output_file
        elif command -v convert >/dev/null 2>&1; then
            convert -resize x${output_size} "${input_file}" $output_file
        else
            echo "No suitable image library found to create: $output_file"
        fi
    done
done