Is there a way to display a countdown or stopwatch timer in a terminal?

I'm not sure why you need beep. If all you want is a stopwatch, you can do this:

while true; do echo -ne "`date`\r"; done

That will show you the seconds passing in realtime and you can stop it with Ctrl+C. If you need greater precision, you can use this to give you nanoseconds:

while true; do echo -ne "`date +%H:%M:%S:%N`\r"; done

Finally, if you really, really want "stopwatch format", where everything starts at 0 and starts growing, you could do something like this:

date1=`date +%s`; while true; do 
   echo -ne "$(date -u --date @$((`date +%s` - $date1)) +%H:%M:%S)\r";
done

For a countdown timer (which is not what your original question asked for) you could do this (change seconds accordingly):

seconds=20; date1=$((`date +%s` + $seconds)); 
while [ "$date1" -ge `date +%s` ]; do 
  echo -ne "$(date -u --date @$(($date1 - `date +%s` )) +%H:%M:%S)\r"; 
done

---

You can combine these into simple commands by using bash (or whichever shell you prefer) functions. In bash, add these lines to your ~/.bashrc (the sleep 0.1 will make the system wait for 1/10th of a second between each run so you don't spam your CPU):

function countdown(){
   date1=$((`date +%s` + $1)); 
   while [ "$date1" -ge `date +%s` ]; do 
     echo -ne "$(date -u --date @$(($date1 - `date +%s`)) +%H:%M:%S)\r";
     sleep 0.1
   done
}
function stopwatch(){
  date1=`date +%s`; 
   while true; do 
    echo -ne "$(date -u --date @$((`date +%s` - $date1)) +%H:%M:%S)\r"; 
    sleep 0.1
   done
}

You can then start a countdown timer of one minute by running:

countdown 60

You can countdown two hours with:

countdown $((2*60*60))

or a whole day using:

countdown $((24*60*60))

And start the stopwatch by running:

stopwatch

---

If you need to be able to deal with days as well as hours, minutes and seconds, you could do something like this:

countdown(){
    date1=$((`date +%s` + $1));
    while [ "$date1" -ge `date +%s` ]; do 
    ## Is this more than 24h away?
    days=$(($(($(( $date1 - $(date +%s))) * 1 ))/86400))
    echo -ne "$days day(s) and $(date -u --date @$(($date1 - `date +%s`)) +%H:%M:%S)\r"; 
    sleep 0.1
    done
}
stopwatch(){
    date1=`date +%s`; 
    while true; do 
    days=$(( $(($(date +%s) - date1)) / 86400 ))
    echo -ne "$days day(s) and $(date -u --date @$((`date +%s` - $date1)) +%H:%M:%S)\r";
    sleep 0.1
    done
}

Note that the stopwatch function hasn't been tested for days since I didn't really want to wait 24 hours for it. It should work but please let me know if it doesn't.

My favorite way is:

Start:

time cat

Stop:

ctrl+c

---

As @wjandrea commented below, another version is to run:

time read

and press Enter to stop

I was looking for the same thing and ended up writing something more elaborate in Python:

This will give you a simple 10-second countdown:

sudo pip install termdown
termdown 10

Source: https://github.com/trehn/termdown