Question 47089 in Debian Question posted in
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tail -f | grep in if statement – Debian

I’m running from bash script something like

$(command -options)&
export SC_PID=$!    
if tail -f <log_filename.txt> | grep --line-buffered -E "(some expression)"; then
        kill -STOP $SC_PID
fi

but it’s writing "(some expression)" in the command line output instead of killing the process. Note that log_filename.txt is a log file where’s being written output from $(command -options) in real time. What am I doing wrong?

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2

Answers


  1. 0

    Your pipe (tail -f ... | grep ...) will never end.

    Add -m 1 to your GNU grep to exit after first match.

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  2. 0

    your if statement with "tail -f" can’t finished until you break it, so it just can’t move to next step. try to split text by lanes, like the following:

    $(command -options)&
export SC_PID=$!    
tail -f <log_filename.txt)|while read; do
  if (echo "$REPLY"|grep --line-buffered -E "(some expression)"); then
    kill -STOP $SC_PID
  fi
done
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