A little function to convert png -> jpg with missing extension detection

png2jpg.sh

#!/bin/bash

function png2jpg() {
    case $1 in
        *.png)
            ;;
        *)
            if [ ! diff <(echo -n ".PNG" ) <(dd if=$1 bs=1 count=4) ]; then
                echo "input file $1 is not a png"
                return 1
            fi

            echo "input file is a suspected png without extension, continuing"
            ;;
    esac

    magick convert "$1" "${1%png}.jpg"
}