From: Doug Gwyn (VLD/VMB) <gwyn at BRL-VLD.ARPA> cc -o foo.c foo.c will not clobber your source on UNIX System V. This trivial safety check (as well as others to keep "cat" from writing the file it is reading and so forth) could easily be added to older versions of UNIX. As to keeping backup copies of source code, that is what SCCS is for.