Convert png to gif with ImageMagick

pngToGif.sh

function pngToGif() {
    while getopts ":i:o:" opt; do
        case $opt in
            i) input_file="${OPTARG}"
                ;;
            o) output_file="${OPTARG}"
                ;;
            \?) echo "Invalid option -${OPTARG}" >&2
                ;;
        esac
    done

    convert -loop 0 "./${input_file}*.png" "./${output_file}.gif"
    rm -- *.png
}