Portable file watcher in bash.

watchfiles.sh

#!/usr/bin/env bash

_usage() {
  printf 'usage: %s [-p|--poll <sec per poll>] [-a|--all] [<find args>] -- <command> [<args>]\n' "$(basename "$0")" >&2
  exit 64
}

# Default arg values
sec_per_poll=2
find_all=false
find_args=()

# Parse args
while [[ "$1" != '--' ]]; do
  case "$1" in
    -p|--poll)
      shift
      sec_per_poll=$1 ;;
    -a|--all)
      find_all=true ;;
    *)
      find_args+=("$1") ;;
  esac

  # Print usage if end of arguments encountered before '--'
  shift || _usage
done

# Shift past '--'
shift

if $find_all; then
  _my_find() {
    find . "$@" -print0
  }
else
  _my_find() {
    find * "$@" -print0
  }
fi

if [[ $(uname) == Darwin ]]; then
  _find_and_hash() {
    _my_find "$@" | xargs -0 -n 100 stat -f'%m' | cksum
  }
else
  _find_and_hash() {
    _my_find "$@" | xargs -0 -n 100 stat -c'%y' | cksum
  }
fi

# Print usage if no find args were given
if [[ -z "${find_args[*]}" ]]; then
  _usage
fi

# Poll for changes every $sec_per_poll seconds
prev_hash=
while true; do
  curr_hash=$(_find_and_hash "${find_args[@]}")

  if [[ $prev_hash != $curr_hash ]]; then
    printf '[%s] Changes detected in files...\n' "$(date)" >&2

    # Execute specified command
    "$@" || printf 'Command exited with status %d\n' $? >&2

    prev_hash=$curr_hash
  fi

  sleep $sec_per_poll
done