•mkdir — Make a directory

•mkdir path makes the directory path and any missing parents, and returns path, which isn’t displayed. With the option unique, it then makes a directory with a new, unique name inside path, and returns that directory’s path, which is displayed, as in ["unique":1] •mkdir •host "temp". The option prefix sets the start of the name, as in ["unique":1 "prefix":"run"] •mkdir dir. The directory stays until removed.

Errors: IO for file errors; DOMAIN for an invalid option, or prefix without unique.