How do you embed strings within the comments within a heredoc?

Question

This doesn't work, the comment doesn't contain the IP_ADDR string

SSH_UN='user'
IP_ADDR='192.168.1.101'

cat <<"EOF" >> .ssh/config
# VirtualBox (VB) on user's laptop at $IP_ADDR
Host laptopvb
  Hostname $IP_ADDR
  User $SSH_UN
  ForwardAgent yes
EOF

Answer 1

Remove the double quotes around the EOF:

IP_ADDR='192.168.1.101'
cat <<EOF >> .ssh/config
# VirtualBox (VB) on hobs laptop at $IP_ADDR
Host laptopvb # manually set as a static IP on the VB
  Hostname $IP_ADDR
  User $SSH_UN
  ForwardAgent yes
EOF

According to the bash manual:

The format of here-documents is:

       <<[-]word
               here-document
       delimiter

No parameter expansion, command substitution, arithmetic expansion, 
or pathname expansion is performed on word. If any characters in word are quoted, 
the delimiter is the result of quote removal on word, and the lines in the
here-document are not expanded. If word is unquoted, all lines of the
here-document are subjected to parameter expansion, command substitution,
and arithmetic expansion.