$ bash test list
sed: -e expression #1, char 1: unknown command: `@'

cat test
#!/bin/bash
while read -r line
do
URL=$(echo "$line" | grep -w "^ht.*")
if [ ! -z "$URL" ]
then
cat $1 |sed -e "@^#@{N;N;@"$URL"@d;}"
fi
done < $1

cat list
#string1
http://site.com/example/example.txt
#string3