As some people know in Unix v6 mv.c could issue a strange error message. Dennis Ritchie wrote about it himself as well as some other fun things in Unix like the famous comment:
/* You are not expected to understand this */
and a funny story about a.out.
If you look at the origin/Research-V6-Snapshot-Development branch of the Unix
History Repository you will
find under usr/source/s2/mv.c which has the original code. It looks like:
if(*--argp1 == '.'){
write(1,"values of ^NB^O will give rise to dom!\n",37);
exit();
}
Or better yet the following screenshot which shows the source in its original form:
As Dennis Ritchie wrote it could also be in the form of:
write(1,"values of \016B\017 will give rise to dom!\n",37);
but this still has the problems.
There are two problems though in getting this to work. The first one is it no longer compiles on modern systems as the C standard is much more strict. But even worse once you fix the code (not hard to do) it no longer works! Instead it will show only:
values of B will give rise to dom!
This is really unfortunate but there's a simple fix. Once this is done you can see the output of the command (as well as how to trigger it):
The point is to include the original uncompilable code, how to make it compilable and then how to fix it so that it works on modern systems.
A note that I haven't fixed any other bugs and I haven't cleaned up the compiler warnings. I could do this but I do not see the point - at least at this time - and I have other things I'd like to do too.
The file mv-v6.c is the original file; the file mv-v6-compiles.c is the file with the compilation errors fixed and the file mv-v6-beta.c is the fix so that it still shows the original message!
Simply run from the directory:
make
This should create two executables, one which will show the incorrect message
(mv-v6) and the other which will show the correct message (mv).
How to do this? If you don't know C it might be harder to figure out but it's
very simple. The first arg must be a . or .. (specifically the first char
of the first arg must be a . and it must be - which of course it is - a
directory) and the second arg must be a non-existent file. Thus the following
invocations will work after compiling the code assuming the file beta does not
exist:
./mv . beta
./mv .. beta
But the following will not work:
./mv foo bar
if there is no file foo or foo is not a file or even if foo is a directory
and bar exists or does not exist.
I only tested one terminal emulator with the output so it's possible it works in
others but I think not because those characters are !isprint() and I don't
think they have their original significance (this I am not sure of).
Although you can try out and trigger the original warning the program should not
be used instead of the modern mv. This was for fun only.