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I was wanting to write a (ba)sh script to allow me to wait for the detection of a new USB device, and when that device is detected, execute some commands. The scripts are intending to be working on the principle that whenever I plug in a usb device a message containing the words "new" and "USB" is appended to /var/log/messages. I want this program to be running in the background of my computer at all times, so I want one that will take as little cpu power as it can when there is nothing for it to do. I have tried to do this two ways: with read and with tail ./fifo_pipe.

My first attempt looked something like this:


tail -f /var/log/messages | grep "new.*USB" | ./ &
disown %
while true
  echo "detected new usb"

This did absolutely nothing.

Then I tried this:

mkfifo pipe
tail -f /var/log/messages | grep "new.*USB" > pipe &
disown %
while true
  tail pipe
  echo "found new USB device"

Just as before it did not output anything.
Any suggestions? I do not want to use udev or automount, but use tail -f /var/log/messages


Hi Sudo! I've done something similar before to monitor a log for errors, and execute commands based on what it found. Here's an example:


tail -fn0 $logfile | while read line ; do
  echo "$line" | grep "$pattern" 
  if [ $? = 0 ]; then
    echo "$line"

I hope this helps! I like the pipe idea, but I haven't tried anything like that yet.

That worked well.

My problem was with grep. When I removed grep from that line everything worked as planed.


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