Clear stdin before reading

Question

I have the following bash script:

# do some time consuming task here
read -p "Give me some input: " input

Now as you might have guessed, if a user presses some random keys during the "time consuming task", the unwanted input is taken into account as well. How do I clear stdin (or at least ignore it) before I issue the read command?

Answer 1

I don't think there is a way to clear stdin but (with bash) you can read and discard what is there before you ask for the input

#do some time consuming task here
read -t 1 -n 10000 discard 
read -p "Give me some input: " input

This reads stdin and has a timeout of 1 second, it fails though if there are more than 10000 chars in stdin. I don't know how big you can make the nchars parameter.

Answer 2

read -d '' -t 0.1 -n 10000

This reads multiple lines of inputs, if the user inadvertently pressed enter multiple times

Answer 3

Enclose the time consuming task in a block whose stdin is closed:

{
     # time consuming task
} <&-

read -p "Give me some input: " input