#!/bin/bash

echo -n "Type garbage..."
sleep 2
echo done.

# Empty keyboard buffer
# 255 characters should suffice...?
read -t 0.1 -N 255

echo -n "Enter value for a: " 
read a
echo "You entered: $a"

Empties the keyboard buffer. Useful to discard keyboard input during a command execution inside a bash script.
Try this script without this line:

read -t 0.1 -N 255

and enter any garbage ([ENTER] and all) during these 2 seconds window...

The modifiers:
-t 0.1       Tiemout read on 0.1 seconds - so read won't wait to get all 255 characters
-N 255    Read 255 characters, treating any special character ([ENTER], tabs, etc.) as normal characters

Empty keyboard buffer

Bash

Bash