Question

First of all, I’m a beginner on shell-script. This code I’ve done is not working.

I want to repeat a code for 30 seconds but it doesn’t work. It just keep doing my logic indefinitely.

DIFF=0

while [ $DIFF < 30 ]; do

    START=$(date +%s)

######## My logic #########

    DIFF=$(( $END - $START ))
    echo $DIFF
    cd ..
    sleep 5s

done

I think it’s because I’m not doing the while clause properly?

Answer 1

Well, you definitely need to provide some values for $START and $END. They won’t set themselves!

You may want to do something like

START = `date +%s` 

to set it to a time in seconds. Of course END will need to be set inside your loop to get it updated.

EDIT: cd .. is hopefully not really what you plan to run inside the loop. Within a few milliseconds your current directory will be the root directory, with little else accomplished. It would be cheaper to do a single cd / .

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EDIT 2: This shouldn’t be such a hard problem. For this edit, I’ve built and tested a one-line solution:

START=$(date +%s); DIFF=0; while [ $DIFF -lt 30 ]; do echo $DIFF; DIFF=$(($(date +%s)-$START)); done

That will correctly update its variables and display them… and it ends after 30 seconds.