How to clear keyboard buffer in ksh?

Question

I'm writing a Korn shell script, and it will read input from the user. I would like to clear the keyboard buffer before calling the "read" command, so that the user doesn't cause problems by impatiently typing ahead. I might add that the intended audience for this script is myself. 🙂

I'm using the OpenBSD ksh, which appears to be a variant of ksh88. I do have ksh93 available, but would prefer to NOT rely on Bash.

Example code:

# Would like to clear stdin buffer here
echo "Are you sure?"
read input

case $input in
    y*|Y*)
        echo "You said yes!"
        ;;
    *)
        echo "You said no!"
        exit 1
        ;;
esac

EDIT: Basically I want to clear ALL data from stdin before calling the "read".

I'm currently experimenting with setting a signal handler for SIGALRM and using trap to implement a timeout on doing a "pre-read".

Answer 1

try like this

read -t 1 garbage;
echo "Are you sure?"
read input

case $input in
    y*|Y*)
        echo "You said yes!"
        ;;
    *)
        echo "You said no!"
        exit 1
        ;;
esac

EDIT: I just realized that this will remove only the first line you can put it in a loop:

while read -t 1 garbage; do
  sleep 0
done

echo "Are you sure?"
read input

case $input in
    y*|Y*)
        echo "You said yes!"
        ;;
    *)
        echo "You said no!"
        exit 1
        ;;
esac