Appending a line to a file only if it does not already exist

Question

I need to add the following line to the end of a config file:

include \"/configs/projectname.conf\"

to a file called lighttpd.conf

Answer 1

If, one day, someone else have to deal with this code as "legacy code", then that person will be grateful if you write a less exoteric code, such as

grep -q -F 'include "/configs/projectname.conf"' lighttpd.conf
if [ $? -ne 0 ]; then
  echo 'include "/configs/projectname.conf"' >> lighttpd.conf
fi