Bash: How to end infinite loop with any key pressed?

Question

I need to write an infinite loop that stops when any key is pressed.

Unfortunately this one loops only when a key is pressed.

Ideas please?

#!/bin/bash

count=0
while : ; do

    # dummy action
    echo -n "$a "
    let "a+=1"

    # detect any key  press
    read -n 1 keypress
    echo $keypress

done
echo "Thanks for using this script."
exit 0

Answer 1

You need to put the standard input in non-blocking mode. Here is an example that works:

#!/bin/bash

if [ -t 0 ]; then
  SAVED_STTY="`stty --save`"
  stty -echo -icanon -icrnl time 0 min 0
fi

count=0
keypress=''
while [ "x$keypress" = "x" ]; do
  let count+=1
  echo -ne $count'\r'
  keypress="`cat -v`"
done

if [ -t 0 ]; then stty "$SAVED_STTY"; fi

echo "You pressed '$keypress' after $count loop iterations"
echo "Thanks for using this script."
exit 0

Edit 2014/12/09: Add the -icrnl flag to stty to properly catch the Return key, use cat -v instead of read in order to catch Space.

It is possible that cat reads more than one character if it is fed data fast enough; if not the desired behaviour, replace cat -v with dd bs=1 count=1 status=none | cat -v.

Edit 2019/09/05: Use stty --save to restore the TTY settings.