Bchdir changes the current working directory (see chdir(2)) to the
directory given by the string pointed to by str. Files referenced with
path names that do not begin with / are located relative to the current
working directory. After the current working directory is changed, the new
directory is used as the base for all relative path names for this process and
any processes it creates. This function implements the CHDIR statement.
Bmkdir creates a new directory with the name given by the string pointed
to by str. This function implements the MKDIR statement.
Brmdir removes the directory with the name given by the string pointed
to by str. This function implements the RMDIR statement.