This works well

gistfile1.txt

x220:/srv/www/greptweet$ cat foo.cgi 
#!/bin/bash
exec 2>&1
cat <<END
Cache-Control: no-cache
Content-Type: text/html

END

./foo-script.sh & disown
x220:/srv/www/greptweet$ cat foo-script.sh 
#!/bin/bash
while true
do
        date=$(date)
        echo "$date"
        echo "$date" >> "foo$$.log"
        echo '<br>'
        sleep 5
done 
x220:/srv/www/greptweet$