fswatch:tldr:6dca5

This command is a combination of several commands and is used for monitoring a file or directory for changes and then executing a specified Bash command whenever a change is detected. Let's break it down:

1. fswatch: This is a command-line utility that is used to monitor files and directories for changes. It takes one or more file or directory paths as arguments and continuously watches for any modifications such as file creation, deletion, or modification.

2. ${filename}: This is a placeholder for the name of the file you want to monitor. You need to replace it with the actual filename.

3. ${path-to-directory}: This is a placeholder for the path to the directory you want to monitor. You need to replace it with the actual directory path.

4. ${path-to-another_directory-*--js}: This is a placeholder for another directory path pattern that matches multiple directories. The pattern allows for the selection of directories based on a specific naming convention (e.g., ending with ".js"). Again, you need to replace it with the actual directory path pattern.

5. | (pipe symbol): This symbol is used to redirect the output of the preceding command to the next command.

6. xargs: This command reads items from standard input (either from a pipe or from command line arguments) and executes a command with those items as arguments.

7. -n 1: This option tells xargs to execute the given command for each item separately (one at a time).

8. ${bash_command}: This is a placeholder for the Bash command you want to execute when a file change is detected. You need to replace it with the actual Bash command.

So, when this whole command is executed, fswatch will monitor the specified file and directories for any changes. Whenever a change is detected, it will pass the name of the file or directory to xargs, which will then execute the specified Bash command (${bash_command}) with the received argument. The -n 1 option ensures that the command is executed for each file or directory change separately.