Write me a bash script that will function as an executable script, which is a persistent bash-alias manager. It should have the capabilities of adding aliases, removing aliases, updating existing aliases (and checking if alias exists before adding,otherwise it will ask the user if they are sure they wish to update the existing alias), listing all current aliases, and a help command covering usage. The appropriate error handling should be incorporated throughout. If there are any other functionalities that you feel would be appropriate for a more complete Linux bash alias manager script, feel free to incorporate those functionalities as well.