How can I check if a package is installed and install it if not?

I’m working on a Ubuntu system and currently this is what I’m doing:

if ! which command > /dev/null; then
   echo -e "Command not found! Install? (y/n) \c"
   read
   if "$REPLY" = "y"; then
      sudo apt-get install command
   fi
fi

Is this what most people would do? Or is there a more elegant solution?