shell script respond to keypress

I have a shell script that essentially says something like ``` while true; do read -r input if ["$input" = "a"]; then echo "hello world" fi done ``` That is all well, and good, but I just realized having to hit ENTER presents a serious problem in this situation. What I need is for the script to respond when a key is pressed, without having to hit enter. Is there a way to achieve this functionality within a shell script?