react is a linux bash script to monitor file modification recursively and execute bash commands as changes occur

react.sh

#!/usr/bin/env bash
# script:  react (renamed from conflicting 'watch' command)
# author:  Mike Smullin <mike@smullindesign.com>
# contributor: Mike Kormendy <mike@somethinginteractive.com>
# license: GPLv3
# description:
#   watches the given path for changes
#   and executes a given command when changes occur
# usage:
#   watch <path> <cmd...>
#

path=$1
shift
cmd=$*
sha=0
update_sha() {
  sha=`ls -lR --time-style=full-iso $path | sha1sum`
}
update_sha
previous_sha=$sha
react() {
  echo -en " reacting...\n\n"
  $cmd
  echo -en "\n--> resumed watching."
}
compare() {
  update_sha
  if [[ $sha != $previous_sha ]] ; then
    echo -n "change detected,"
    react
    previous_sha=$sha
  fi
}
trap react SIGINT
trap exit SIGQUIT

echo -e  "--> Press Ctrl+C to force reaction, Ctrl+\\ to exit"
echo -en "--> watching \"$path\""
while true; do
  compare
  sleep 1
done