A cross-platform file change monitor. More information: https://emcrisostomo.github.io/fswatch.
fswatch path/to/file | xargs -n 1 bash_command
fswatch path/to/file path/to/directory path/to/another_directory/**/*.js | xargs -n 1 bash_command
fswatch path/to/directory | xargs -n 1 -I {} echo {}
fswatch --event Updated|Deleted|Created path/to/directory | xargs -n 1 bash_command