#!/bin/bash

while IFS=, read -r from to
do
    echo copying from $from to $to
    cp -vufr "$from" "$to" 2>> ~/cperrors.txt
done <<EOF
/home/myuser/important_files/,/media/myuser/externalHD/backup/important_files
/home/myuser/another_dir/,/media/myuser/externalHD/backup/another_dir
EOF