Adding Counter in shell script

Question

I have below code in my shell script which will keep on sleeping if it doesn't finds any file. And it sleeps for half an hour but currently I don't have any counter like only execute the below code 20 times and then exit the program if the files are still are not there (means don't do anything after 20 checks and exit the full script).

What's the best way to do this problem? So that I am also aware by looking at the emails that it has tried 20 times.

Hope I am clear enough.

while true; do   if /home/hadoop/latest/bin/hadoop fs -ls /apps/hdtech/bds/quality-rt/dt=$DATE_YEST_FORMAT2 then        echo "Files Present" | mailx -s "File Present"  -r [email protected] [email protected]        break   else        echo "Sleeping for half an hour" | mailx -s "Time to Sleep Now"  -r [email protected] [email protected]        sleep 1800   fi done 

Answer 1

Here's how you might implement a counter:

counter=0 while true; do   if /home/hadoop/latest/bin/hadoop fs -ls /apps/hdtech/bds/quality-rt/dt=$DATE_YEST_FORMAT2 then        echo "Files Present" | mailx -s "File Present"  -r [email protected] [email protected]        exit 0   elif [[ "$counter" -gt 20 ]]; then        echo "Counter: $counter times reached; Exiting loop!"        exit 1   else        counter=$((counter+1))        echo "Counter: $counter time(s); Sleeping for another half an hour" | mailx -s "Time to Sleep Now"  -r [email protected] [email protected]        sleep 1800   fi done 

Some Explanations:

• counter=$((counter+1)) - this is how you can increment a counter. The $ for counter is optional inside the double parentheses in this case.
• elif [[ "$counter" -gt 20 ]]; then - this checks whether $counter is not greater than 20. If so, it outputs the appropriate message and breaks out of your while loop.

Answer 2

Try this:

counter=0 while true; do   if /home/hadoop/latest/bin/hadoop fs -ls /apps/hdtech/bds/quality-rt/dt=$DATE_YEST_FORMAT2 then        echo "Files Present" | mailx -s "File Present"  -r [email protected] [email protected]        break   elif [[ "$counter" -gt 20 ]]; then        echo "Counter limit reached, exit script."        exit 1   else        let counter++        echo "Sleeping for another half an hour" | mailx -s "Time to Sleep Now"  -r [email protected] [email protected]        sleep 1800   fi done 

Explanation

• break - if files are present, it will break and allow the script to process the files.
• [[ "$counter" -gt 20 ]] - if the counter variable is greater than 20, the script will exit.
• let counter++ - increments the counter by 1 at each pass.