Simple Directory watcher

dir_watcher.sh

#!/bin/bash

# Function to watch a directory for changes on macOS and execute a command.
# Requires fswatch to be installed (e.g., via Homebrew: brew install fswatch).
# Usage: watch_dir <directory> <command>
#
# Arguments:
#   <directory>: The directory to watch for changes.
#   <command>: The command to execute when a change is detected.

function watch_dir {
  if [ "$#" -lt 2 ]; then
    echo "Usage: watch_dir <directory> <command>"
    return 1
  fi

  local directory="$1"
  local command="$2"

  if [ ! -d "$directory" ]; then
    echo "Error: Directory '$directory' not found or is not a directory."
    return 1
  fi

  # Check if fswatch is installed
  if ! command -v fswatch &> /dev/null
  then
      echo "Error: fswatch is not installed."
      echo "Please install it, e.g., using Homebrew: brew install fswatch"
      return 1
  fi

  echo "Watching directory: '$directory' (macOS)"
  echo "Executing command on change: '$command'"
  echo "Press Ctrl+C to stop."

  # Use fswatch to monitor the directory recursively for any events
  # and execute the command on each event using xargs.
  # -r: Monitor recursively
  # -0: Use null character as delimiter (for safety with filenames containing spaces)
  fswatch -r -0 "$directory" |
  xargs -0 -n 1 -I {} bash -c "$command"
}

Example usage:

watch_dir '.' 'ruby main.rb'