A simple stopwatch in Bash

stopwatch.sh

#!/bin/bash

replace_line() { printf "\r\e[K$1 " ${@:2}; }
wait_enter() { read -s; }

now() { echo $( date +%s.%N ); }

time_format() {
    a=$( printf "%.2f " $1 )
    m=$( printf "%d" $( echo $a / 60 | bc ) )
    if [ "$m" -ne "0" ]
    then
        s=$( printf "%05.2f" $( echo $a % 60 | bc ) )
        replace_line "%s:%s " $m $s
    else
        s=$( printf "%.2f" $( echo $a % 60 | bc ) )
        replace_line "%s " $s
    fi
}

eechoo() {
    while sleep 0.05
    do
        d=$( echo $(now) - $1 | bc )
        replace_line "%s " $( time_format $d )
    done
}

t=$( now )
eechoo $t &
while wait_enter
do
    kill %%
    d=$( echo $(now) - $t | bc )
    replace_line "%s PAUSED " $( time_format $d )
    wait_enter
    d2=$( echo $(now) - $t | bc )
    t=$( echo $t + $d2 - $d | bc )
    eechoo $t &
done 2>/dev/null