Time condition loop in shell

Question

I have just started learning shell script recently, so I don\'t know much about it.

I am trying to find example of time based while loop but not having any luck.

Answer 1

You can explore the -d option of date.

Below is a shell script snippet to exemplify. It is similar to other answers, but may be more useful in different scenarios.

# set -e to exit if the time provided by argument 1 is not valid for date.
# The variable stop_date will store the seconds since 1970-01-01 00:00:00
# UTC, according to the date specified by -d "$1".
set -e
stop_date=$(date -d "$1" "+%s")
set +e

echo -e "Starting at $(date)"
echo -e "Finishing at $(date -d "$1")"

# Repeat the loop while the current date is less than stop_date
while [ $(date "+%s") -lt ${stop_date} ]; do

    # your commands that will run until stop_date

done

You can then call the script in the many different ways date understands:

$ ./the_script.sh "1 hour 4 minutes 3 seconds"
Starting at Fri Jun  2 10:50:28 BRT 2017
Finishing at Fri Jun  2 11:54:31 BRT 2017

$ ./the_script.sh "tomorrow 8:00am"
Starting at Fri Jun  2 10:50:39 BRT 2017
Finishing at Sat Jun  3 08:00:00 BRT 2017

$ ./the_script.sh "monday 8:00am"
Starting at Fri Jun  2 10:51:25 BRT 2017
Finishing at Mon Jun  5 08:00:00 BRT 2017