4.3 rcp can clobber a source file; does not understand host.user:file

[Ron Natalie <ron>]

Subject: RCP clobbers files.
Index:	bin/rcp.c 4.3BSD

Description:
	Rcp will silently make a file zero lenght if it is specified
	as both the source and destination of a copy.  It is difficult
	to predict when this will happen as there is no sure way to
	verify that two CPU's are in fact using the same filesystem.
	In addiiton, when rcp is called with one argument it just silently
	exit without saying anything.

Repeat-By:
	1.	create a file with non-zero lenght called foo on machine host
		issue command on host:  rcp host:foo foo
		the file will now be zero length.
	2.	type "rcp foo"
Fix:
	Make rcp non-destructive in it's copies.  Rather than doing an
	initial creat, just open the file. Then copy all the blocks.
	When the files are the same, each block will be read and written
	back into the same place it was read.
	Then do an ftruncate to fix up the file length.

	Add usage message when too few arguments.

*** 118,123 ****
--- 114,125 ----
  		}
  	}
  	rem = -1;
+ 
+ 	if(argc <= 1){
+ 		fprintf(stderr,"Usage: rcp [-p] f1 f2; or: rcp [-rp] f1...fn d2\n");
+ 		exit(1);
+ 	}
+ 	
  	if (argc > 2)
  		targetshouldbedirectory = 1;
  	(void) sprintf(cmd, "rcp%s%s%s",
***************
*** 605,611 ****
  			}
  			continue;
  		}
! 		if ((of = creat(nambuf, mode)) < 0) {
  	bad:
  			error("rcp: %s: %s\n", nambuf, sys_errlist[errno]);
  			continue;
--- 607,613 ----
  			}
  			continue;
  		}
! 		if ((of = open(nambuf, O_WRONLY|O_CREAT, mode)) < 0) {
  	bad:
  			error("rcp: %s: %s\n", nambuf, sys_errlist[errno]);
  			continue;
***************
*** 649,654 ****
--- 651,657 ----
  		if (count != 0 && wrerr == 0 &&
  		    write(of, bp->buf, count) != count)
  			wrerr++;
+ 		ftruncate(of, size);
  		(void) close(of);
  		(void) response();
  		if (setimes) {