Exiting while loop bash script from tail

Question

I have a script that tails a log file, and then uploads the line. I would like to have it exit as soon as the first line is read:

#!/bin/bash

tail -n0 -F "$1" | while read LINE; do
  (echo "$LINE" | grep -e "$3") && curl -X POST --silent --data-urlencode \
    "payload={\"text\": \"$(echo $LINE | sed "s/\"/'/g")\"}" "$2";
done

Exit as soon as the first line is read? Or when the first data is uploaded? — MrJLP
– MrJLP, Commented Jul 17, 2017 at 22:43
What if the first line read doesn't match what's passed in as the third arg? — MrJLP
– MrJLP, Commented Jul 17, 2017 at 22:44
Right now it uploads on each line added that contains the third arg of the script ($3) — MrJLP
– MrJLP, Commented Jul 17, 2017 at 22:45
The third arg is the url to which it writes. ex: bash log-tail.sh log_4 localhost:5000/utils/log/4 — George L
– George L, Commented Jul 17, 2017 at 22:47

MrJLP · Accepted Answer · 2017-07-17 22:49:45Z

1

If you want to exit as soon as the first line is uploaded you can just add a break:

#!/bin/bash

tail -n0 -F "$1" | while read LINE; do
  (echo "$LINE" | grep -e "$3") && curl -X POST --silent --data-urlencode \
    "payload={\"text\": \"$(echo $LINE | sed "s/\"/'/g")\"}" "$2" && break;
done

answered Jul 17, 2017 at 22:49

MrJLP

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George L · Accepted Answer · 2017-07-18 00:12:56Z

1

The issue was the tail command wasn't getting killed. A slightly modified version of my script (I didn't end up needing the echo to stdout)

#!/bin/bash

tail -n0 -F "$1" | while read LINE; do
    curl -X POST --data-urlencode "payload={\"text\": \"$(echo $LINE | sed "s/\"/'/g")\"}" "$2" && pkill -P $$ tail
done

This answer helped as well: https://superuser.com/questions/270529/monitoring-a-file-until-a-string-is-found

answered Jul 18, 2017 at 0:12

George L

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