code:

#!/bin/bash

apod_url="https://apod.nasa.gov/apod/"
apod_out="response.out"
image_name="apod"

echo "Requesting URL: $apod_url"
response="$(curl -s $apod_url)"

echo "Writing response to file: $apod_out"
echo "$response" > $apod_out

#response="$(<$apod_out)"

image_file="$(sed -n '1,//s/.*href=\"\(image.\+\..\{3\}\)\">/\1/p' <<< $response)"

echo "Image file: $image_file"

if [ "$image_file" != "" ]; then
    image_ext="$(sed -n 's/.*\(\..\{3\}\).*/\1/p' <<< $image_file)"
    image_out="$image_name$image_ext"
    image_download_url="$apod_url$image_file"

    echo "APOD image URL: $image_download_url"
    echo -n "Downloading to $image_out... "

    curl -s -o "$image_out" "$image_download_url"

    echo "Done."
else
    echo "APOD image URL not found"
    echo "Exiting."
fi