The default shell in macOS Big Sur is zsh. To change your shell, please do the following:
1. Open the Terminal application.
2. To list available shells, type cat /etc/shells.
3. To update your account to use bash run chsh -s /bin/bash
4. After making the change, close the Terminal app.
5. After you open Terminal again, your shell will be bash.
6. To confirm, type echo $SHELL in Terminal.
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