Create iconset from a PNG

make_icns.zsh

#!/bin/zsh

## Makes an icon set from a PNG. A 512x512 or 1024X1024 PNG is best.
## Taken from http://stackoverflow.com/a/31150333
## Usage: ./make_icns.zsh </path/to/image.png>

NAME=$(basename $1 .png); DIR="$NAME.iconset"
mkdir -pv $DIR
for m r in 'n' '' '((n+1))' '@2x'; do
    for n in $(seq 4 9 | grep -v 6); do
        p=$((2**$m)); q=$((2**$n))
        OUT="$DIR/icon_${q}x${q}${r}.png"
        sips -z $p $p $1 --out $OUT
    done
done
iconutil -c icns $DIR
rm -frv $DIR