watchdo: Linux bash script to monitor file modifications recursively & execute bash commands as changes occur

watchdo.sh

#!/usr/bin/env bash
# script:  watchdo
# author:  Mike Smullin <mike@smullindesign.com>
# modified: Jared Blalock <mb@molotovbliss.com>
# possible use for monitoring .less changes to compile to .css
# 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

echo -en "Generating checksum from $path ...\n\n"

update_sha() {
  # NOTE: If checksum generation is slow try a smaller size directory.
  sha=`ls -lR --time-style=full-iso $path | sha1sum`
  #sha=`find $path -type f -exec stat -c '%y %s %n *' '{}' + | sha1sum`
}
update_sha
previous_sha=$sha
build() {
  echo -en "Executing: $cmd ...\n\n"
  $cmd -s
  echo -en "Resuming watch: $path "
}
compare() {
  update_sha
  if [[ $sha != $previous_sha ]] ; then
    echo -n " >> Change detected! << \n\n"
    build
    previous_sha=$sha
  else
    echo -n .
  fi
}
#trap build SIGINT
#trap exit SIGQUIT

echo -en  " Press Ctrl+C to  exit.\n"
echo -en " ... watching \"$path\"."
while true; do
  compare
  sleep 1
done