Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1     9/27/83; site hplabs.UUCP
Path: utzoo!watmath!clyde!floyd!harpo!seismo!hao!hplabs!Hpda
From: Hpda@hplabs.UUCP (HP Data Systems)
Newsgroups: net.bugs.4bsd
Subject: Re: dd(1) trashes file if input and output same
Message-ID: <2804@hplabs.UUCP>
Date: Tue, 27-Mar-84 13:10:30 EST
Article-I.D.: hplabs.2804
Posted: Tue Mar 27 13:10:30 1984
Date-Received: Fri, 30-Mar-84 01:32:25 EST
References: <2766@hplabs.UUCP>, <2310@watcgl.UUCP>
Organization: Hewlett Packard Labs, Palo Alto CA
Lines: 26

[Sorry if anyone sees this post twice...]
The case of "dd if=foo >foo" (which is equivalent to "cat foo >foo")
is STILL a lose.

CSH opens the output file (the result of the redirection) before the
command is invoked - whether it be dd(1) or cat(1) or whatever(9).
The result is a truncated file.  However you do get a reprieve if
noclobber is set.  cat(1) chooses to tell you about your mistake,
but you can still kiss your file goodbye.
    % cat foo
    beef
    % cat foo >foo
    cat: input foo is output
    % cat foo
    %					(Where's the beef ?)

About copying from "special" devices, point taken.  I was lazy.
The test should be made for S_IFCHR or S_IFBLK as in cat(1).
Hack in the added tests with change bars (is this sufficient ?):

		if ( stat(ofile,&sbuf_out) == 0 &&
|		     sbuf_in.st_mode != S_IFCHR &&
|		     sbuf_in.st_mode != S_IFBLK &&
		     sbuf_in.st_dev == sbuf_out.st_dev &&
		     sbuf_in.st_ino == sbuf_out.st_ino ) {