How to execute the same loop for 1 hour in bash/ linux scripting?

Question

I want to open and close some web pages with random intervals for an hour.

So far i have written the innards

FILE=webpages
TIMES=0
while test $TIMES -lt 10
do
    #Picks random line(Website) from FILE
    TEMPWEB=`shuf -n 1 $FILE`
    echo "Opening" $TEMPWEB
    #Opens TEMPWEB
    xdg-open $TEMPWEB
    sleep 10
    #Kills firefox
    ps -e | grep firefox | sed 's/\(.[0-9]*\).*/\1/' | xargs kill
    TIMES=$(($TIMES+1))
done

So I'm am missing the while condition.
I want something like:

TIMER = 0h 0m 0s
while( TIMER < 1 h)
   ....
done

Is this possible?

PS. what's the command to random number?

Answer 1

Surely. Try:

#!/bin/bash
START=`date +%s`
while [ $(( $(date +%s) - 3600 )) -lt $START ]; do
    ....
done

date +%s shows the current time in seconds since 1970. The loop computes the current date of an hour ago and checks if it exceeds the start time.

Answer 2

One way you can do this is with signals and traps. Here's a simple example:

#!/bin/bash

me=$$

# Start a background process to signal us when the time has passed
(
        sleep 10
        kill -USR1 $me
) &

# When we recieve SIGUSR1, commit suicide
trap "kill $me" SIGUSR1

# Do stuff until we commit suicide
while [ 1 -eq 1 ]
do
        echo 'Hello!'
        sleep 1
done

The comments are self-explanetory (I hope). The first part kicks off a background process that just sleeps for a period of time (10 seconds in this example), and then when it wakes up sends SIGUSR1 to the originating process.

The shellscript catches this (with trap) and just issues a kill to its own PID, stopping the process.

The rest of it is just an infinite loop -- it's the trap that kills the script and terminates the loop.

Technically you don't need the trap in the example above: the background process could just issue kill $me directly, but I've included it for completeness as you can use it as a hook to do other things (e.g., if you don't want to die but set a flag and have the loop terminate naturally, or you have some clean-up to do before terminating).

Answer 3

This is my solution :

#!/bin/bash

# function to display a number in a range
randrange() { echo $(( ( RANDOM % ($2 - $1 +1 ) ) + $1 )); }

# sleep 1 hour and keep backgrounded PID in a variable
sleep 3600 & _suicide_pid=$!

# while the process is UP
while kill &>/dev/null -0 $_suicide_pid; do
    # ----->8--- do what you want here <---8<-----
    sleep $(randrange 10 15) # random sleep in 10-15 range
done