How can I break a tail -f
in bash? Since this question is related to this question
tail -f | awk and end tail once data is found
I tried the following:
#! /bin/bash
tvar="testing"
(set -o pipefail && tail -f <<< "$tvar" | awk '{print; exit} END{ exit 1}' )
But the script is still hanging on to tail -f
Well, the problem is not the tail -f
but the awk
which hangs. It is meant to terminate when EOF is found (with exit 1
). But there is no EOF found; the tail -f
does not terminate, so there comes no EOF.
Would the awk
terminate, then this would also break the pipe and the tail
would receive a SIGPIPE (which would terminate it).
You must find a different condition on which to terminate.
EDIT:
To achieve what you want you can start the tail -f
in the background, remember its PID and kill it as soon as you do not need it anymore. Running in the background and using a pipe at the same time is tricky. The easiest way to do it would be to use a named pipe (FIFO):
mkfifo log.pipe
tail -f log > log.pipe & tail_pid=$!
awk ... < log.pipe
kill $tail_pid
rm log.pipe
It seems that switching from using <<<
to echo "$tvar" | tail -f
echo "$tvar" | tail -f
does what you want instead?
$> cat test.sh
#! /bin/bash
tvar="testing"
(set -o pipefail && echo "$tvar" | tail -f | awk '{print} END{ exit 1}' )
$> ./test.sh
testing
$>
Although the awk doesn't print anything out afterwards.
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