inotifywait example

inotify-hack

#!/bin/bash
# just an example using inotifywait. the 'process' function basically reads from
# the output of inotifywait and then when it is found what it is after it will kill the
# inotifywait process.
#
# used this to hack a dpkg postinst script that wasnt yet installed and enable some debugging
# in it before it was run.
LAUNCH_PID=""
LOG="/run/${0##*/}.log"
set -f

cleanup() {
   if [ -n "$LAUNCH_PID" -a -e "/proc/$LAUNCH_PID" ]; then
      echo "$$ killing $LAUNCH_PID"
      kill "$LAUNCH_PID"
   fi
}

launch() {
    echo $$
    #exec inotifywait --monitor --recursive --event=modify,create /var/lib/dpkg/info
    exec inotifywait --monitor --recursive /var/lib/dpkg/info
}

process() {
    echo "process: pid=$$"
    read LAUNCH_PID
    echo "process: launch_pid=$LAUNCH_PID"
    while :; do
        read dir op file other
        ret=$?
        [ $ret -eq 0 ] || { echo "read failed: $ret"; exit $ret; }
        echo "ret=$ret dir=$dir op=$op file=$file${other:+ other=${other}}"
        fpath="$dir$file"
        if [ "$file" = "apache2.postinst" ]; then
            echo "modifying $fpath"
            sed -i -e 's,set -e$,set -ex,' "$fpath"
            ret=$?
            echo "ret=$? fixed $fpath"
            exit $ret
        fi
    done
}

if [ "$1" = "process" ]; then
   process
elif [ "$1" = "launch" ]; then
   launch
else
   trap cleanup EXIT
   exec >"$LOG" 2>&1
   echo "parent $$"
   "$0" launch | process
fi
exit