link() - link a file to another

void link( string original, string reference );

Creates  a  link  <reference> to the file <original>.  This efun causes
valid_link(original, reference) to be called in the master object.   If
valid_link() returns 0, the link() call fails.  If valid_link() returns
1 then the link() suceeds iff rename() would succeed if called with the
same arguments.

Note: This efun creates a hard link, not a symbolic one.
https://www.geeksforgeeks.org/difference-between-hard-link-and-soft-link/

rm(3), rmdir(3), rename(3), mkdir(3), cp(3)