> I had to [...] and set my shell to bash/zsh Most likely a command in your script (or one source-d into it) makes an assumption about your $SHELL or login she

> I had to [...] and set my shell to bash/zsh Most likely a command in your script (or one source-d into it) makes an assumption about your $SHELL or login shell that is true for bash/zsh but not for fish. Merely adding a shebang won't fix such a script.