With macOS Catalina, Apple is now using Zsh as the default shell. We love Zsh, but the trusty old Bash shell is still included with macOS, and you can quickly switch back to Bash if you prefer.
Zsh is only the default shell on newly created user accounts, so any existing accounts you have on an upgraded Mac will still use Bash by default unless you change it. Each user account has its own default shell preference.
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