A Unix shell.

A GNU project.

… write the definition line … … move Bash config in here …

A portable shebang: #!/usr/bin/env bash

Apple changed the default shell on macOS from Bash to Zsh because the GNU project re-licensed Bash from GPL 2 to GPL 3 that enforces strict ethics and freedom. Apple shipped the old version of Bash for a while and then switched to Zsh.

1. Install modern Bash with brew install bash
2. Add /opt/homebrew/bin/bash to /etc/shells.
3. Run chsh -s /opt/homebrew/bin/bash
4. check that a FILE exists: test -f FILE

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