Countdown Alarm

written on Saturday, February 9, 2008

Recently I was looking for a "countdown alarm clock" in Linux and decided to write a Bash script to do the job. The goal was to allow the user to enter a target date and time, then display a clock with the remaining time. An example of the output is below.

Features:

Remaining time stays at top left corner of the screen and continuously updates.
Update: Output time inserted in Xterm title bar.
Target time can be specified using natural language string. (i.e. Feb 21 5PM 2010)
Remaining time displayed in years, months, days, hours, minutes, and seconds remaining.
Year, month, and day output is optional depending on the length of the remaining time.

Implementation:

It might seem complicated to do this, but the Unix 'date' utility handles almost all of the program logic for us. For example, to convert a generic date string into the number of seconds from Jan 1st, 1970:

$ date -d "DATE STRING" +%s

The date command can then easily do the reverse operation, using the output of the first command, where "SECONDS" is number of seconds from Jan 1st, 1970:

$ date -d @SECONDS

Some screen drawing tricks were accomplished with special terminal escape commands. These are used to move the cursor out of the way, and clear the line before each update.

Code: countdown.sh

#!/bin/bash
BLINK=1
INPUT_DATE=$@
STOP=`date -d "$INPUT_DATE" +%s`
[ $? == 0 ] || exit -1

function print_time
{
   echo -ne "\033]0;$@\007"   # update window title
   echo -ne "$@"              # update terminal
}

clear

while [ 1 ]; do
   NOW=`date +%s`
   TIME=''

   if [ $STOP -gt $NOW ]; then
      REMAIN=$[ $STOP - $NOW ]

      YEAR=`date -u -d @$REMAIN +%Y`
      YEAR=$[ $YEAR - 1970 ]
      [ $YEAR -gt 0 ] && TIME="${TIME}$YEAR year"
      [ $YEAR -gt 1 ] && TIME="${TIME}s"
      [ $YEAR -gt 0 ] && TIME="${TIME}, "

      MONTH=`date -u -d @$REMAIN +%_m`
      MONTH=$[ $MONTH - 1 ]
      [ $MONTH -gt 0 ] && TIME="${TIME}$MONTH month"
      [ $MONTH -gt 1 ] && TIME="${TIME}s"
      [ $MONTH -gt 0 ] && TIME="${TIME}, "

      DAY=`date -u -d @$REMAIN +%_d`
      DAY=$[ $DAY - 1 ]
      [ $DAY -gt 0 ] && TIME="${TIME}$DAY day"
      [ $DAY -gt 1 ] && TIME="${TIME}s"
      [ $DAY -gt 0 ] && TIME="${TIME}, "

      TIME="${TIME}`date -u -d @$REMAIN +%T`"
      print_time $TIME
   else
      [ $BLINK -eq 1 ] && print_time "00:00:00"
      [ $BLINK -eq 0 ] && print_time ""
      BLINK=$[ $BLINK ^ 1 ]
   fi

   echo -ne "\e[s"            # save cursor position
   echo -ne "\e[1000;1000f"   # move cursor to bottom right of screen

   sleep 0.5
   echo -ne "\e[u"   # restore cursor position
   echo -ne "\r"     # move cursor to start of line
   echo -ne "\e[0K"  # clear line
done

This entry was tagged bash and utility

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Countdown Alarm

Features:

Implementation:

Code: countdown.sh