How to Fix: /bin/bash shell (macOS) throwing `-bash: declare: -A: invalid option` error message at shell start

                The primary reason for this issue is that you changed your default shell from bash to fish using the `chsh` command, but did not properly revert back to bash afterwards. When you switched shells, Fish's configuration files were added to the `/etc/shells` list, which caused the error.Another possible cause is that you used the wrong commands to switch between the two shells. Using both `echo /usr/local/bin/fish | sudo tee -a /etc/shells` and `chsh -s /usr/local/bin/fish`, or using the reverse steps without properly removing Fish's configuration files, could lead to this issue.

            🔧 Proven Troubleshooting Steps

                Reverting Shell Changes Using Correct Commands

                    Step 1: Firstly, remove the incorrect shell configuration files from the `/etc/shells` list by running `sudo rm /usr/local/bin/fish | sudo tee -a /etc/shells`. This will ensure that Fish's configuration is no longer added to the list.Step 2: Next, run the correct command to switch back to bash using only one of the following commands: `echo /bin/bash | sudo tee -a /etc/shells` or `chsh -s /bin/bash`. Avoid using both commands as this can cause further issues.Step 3: After switching back to bash, update your account to use the new shell by running `chsh -s /bin/zsh`. This will ensure that your system is properly configured and you can avoid any potential issues with shell compatibility.



                Using a Third-Party Tool to Revert Shell Changes

                    Step 1: Alternatively, you can use the `chfn` command to revert back to bash. First, run `sudo chfn -i /bin/bash`. This will update your shell configuration and ensure that you are using the correct shell.Step 2: Next, run `sudo chsh -s /bin/bash` to switch back to bash. This will update your system configuration and ensure that you can use bash as your default shell.


            💡 Conclusion
            To resolve the '-bash: declare: -A: invalid option' error, you need to properly revert back to bash after changing shells using the correct commands or a third-party tool. By following these steps, you should be able to resolve this issue and use bash as your default shell on macOS Catalina.