Question

Example usage that works on Ubuntu and other forms of Linux but not on Mac OS X.

while true; do
  read -e -n 1 -p "Do you like Pie? > " -i y ANSWER 
    case $ANSWER in
       [Nn]* ) exit;;
       [Yy]* ) `./calculate-pi.sh`; break;;
       * ) echo "Please answer y or n.";;
    esac
done

Answer 1

Looks like the -i flag was introduced with Bash 4.x. OS X still ships with Bash 3.2.48(1)-release. I don’t think there’s any way to preload the answer with text in Bash 3.x. Typically this is solved by treating the empty response as the default, and indicating this in the prompt (e.g. "Do you like Pie? [Yn]> ").