Ever needed a well formatted countdown (aka tea timer) in your console?

countdown.sh

#!/bin/bash
#
# Simple tea timer
#

start=$(date +%s)

function print_help() {
 cat <<EOF 
usage: $(basename $0) DRUATION
  DURATION is a positive number followed by 
  s for seconds (the default)
  m for minutes
  h for hours or
  d for days
EOF
  exit 1
}

if [[ $1 =~ ([[:digit:]]+)([smhd])? ]]; then
    NUMBER=${BASH_REMATCH[1]} 
    UNIT=${BASH_REMATCH[2]:-s}
  else
   print_help
fi

num=$NUMBER

case $UNIT in
  m)
  num=$((num*60))
  ;;
  h)
  num=$((num*60*60))
  ;;
  d)
  num=$((num*60*60*24))
  ;;
esac

while true; do
    sec_rem=$(($num - ($(date +%s) - $start)))   
    printf "\r\t%02dh:%02dm:%02ds\t" $((sec_rem /3600)) $((sec_rem % 3600 /60)) $((sec_rem % 60))
    [ $sec_rem -le 0 ] && { echo; exit 0; }
   sleep 1
done