[root@station78 ~]# cat counting_down.sh

#!/bin/sh # #@@@author: Majesty # #set -x #a shell for count down #modify the values of time arbitrarily time="01:00:10" #spilt minute and second , and convert them. echo $time > /tmp/tmptime.txt htime=`cat /tmp/tmptime.txt | awk -F: '{print $1}'` case $htime in 00) htime=0;; 01) htime=1;; 02) htime=2;; 03) htime=3;; 04) htime=4;; 05) htime=5;; 06) htime=6;; 07) htime=7;; 08) htime=8;; 09) htime=9;; *);; esac mtime=`cat /tmp/tmptime.txt | awk -F: '{print $2}'` case $mtime in 00) mtime=0;; 01) mtime=1;; 02) mtime=2;; 03) mtime=3;; 04) mtime=4;; 05) mtime=5;; 06) mtime=6;; 07) mtime=7;; 08) mtime=8;; 09) mtime=9;; *);; esac stime=`cat /tmp/tmptime.txt | awk -F: '{print $3}'` case $stime in 00) stime=0;; 01) stime=1;; 02) stime=2;; 03) stime=3;; 04) stime=4;; 05) stime=5;; 06) stime=6;; 07) stime=7;; 08) stime=8;; 09) stime=9;; *);; esac #set -x #change all time to seconds ctime=`echo " $htime*3600 + $mtime*60 + $stime " | bc` #begin counting down while [ $ctime -gt 0 ] do  sleep 1  ctime=$((ctime-1)) clear  #clear screen. ohtime=`expr $ctime / 3600`  #calcuate the hours case $ohtime in 0) ohtime=00;; 1) ohtime=01;; 2) ohtime=02;; 3) ohtime=03;; 4) ohtime=04;; 5) ohtime=05;; 6) ohtime=06;; 7) ohtime=07;; 8) ohtime=08;; 9) ohtime=09;; *);; esac #set -x omtimetmp=`echo "$ctime - $ohtime * 3600" | bc` #calculate the minutes omtime=`expr $omtimetmp / 60` case $omtime in 0) omtime=00;; 1) omtime=01;; 2) omtime=02;; 3) omtime=03;; 4) omtime=04;; 5) omtime=05;; 6) omtime=06;; 7) omtime=07;; 8) omtime=08;; 9) omtime=09;; *);; esac ostime=`expr $ctime % 60` #cut the remainder. calculate the seconds case $ostime in 0) ostime=00;; 1) ostime=01;; 2) ostime=02;; 3) ostime=03;; 4) ostime=04;; 5) ostime=05;; 6) ostime=06;; 7) ostime=07;; 8) ostime=08;; 9) ostime=09;; *);; esac echo "$ohtime:$omtime:$ostime" done @@@test   [root@station78 ~]# ./counting_down.sh ++ echo '3608 - 01 * 3600' ++ bc + omtimetmp=8 ++ expr 8 / 60 + omtime=0 + case $omtime in + omtime=00 ++ expr 3608 % 60 + ostime=8 + case $ostime in + ostime=08 + echo 01:00:08 01:00:08 + '[' 3608 -gt 0 ']' + sleep 1