[kevarh]

Vi (and ed) are the only text editors required to be included in the POSIX spec. A base Unix (and most Linux) installs will have some version of vi or vim installed by default.

If I'm working on someone else's box this pretty much guarantees I can edit files with my basic vi knowledge without having to install a different editor.

[jcfields]

That's why I learned vi initially years ago, because I was told it was the only editor that would always be available anywhere you went. I only ever use it in ssh sessions these days, but I still feel like learning how to use it has paid off many times.

I was playing with Haiku recently and was surprised that vi or vim wasn't included in its base install. Granted, Haiku (like BeOS before it) doesn't ever claim to be a Unix-like or POSIX-compliant system, but I found the CLI environment to be very Unix-like overall. I guess it's a testament to the ubiquity of vi that it never occurred to me that it wouldn't be there. (If anyone's curious, emacs is also absent but nano is there.)

[waddlesplash]

Haiku does actually claim to be POSIX compliant generally, and is certainly UNIX-like. We don't include "vi" in the base install, though.

[tennineeight]

That also happened with NixOS. But then again, not really surprising for something that breaks FHS.

[boomlinde]

Vi is not strictly required; only if POSIX2_UPE and POSIX2_CHAR_TERM are defined.