>From 15e3305905d256a13b6d85a09c199c321d369ba8 Mon Sep 17 00:00:00 2001
From: Bernhard Voelker <address@hidden>
Date: Thu, 19 Feb 2015 01:41:50 +0100
Subject: [PATCH] tee: treat '-' operand as file name as mandated by POSIX

Since v5.2.1-1247-g8dafbe5, tee(1) treated '-' as stdout while POSIX
explicitly requires to treat this as a file name.  Revert this change,
as the interleaved output - due to sending another copy of input to
stdout - is not considered to be useful.  Discussed in
http://lists.gnu.org/archive/html/coreutils/2015-02/msg00085.html

* src/tee.c (tee_files): Remove the special handling for "-" operands.
(usage): Remove the corresponding sentence.
* doc/coreutils.texi (common options): Remove the "tee -" example.
(tee invocation): Document that tee(1) now treats "-" as a file name.
* tests/misc/tee.sh: Add a test case.
* NEWS (Changes in behavior): Mention the change.
---
 NEWS               |  4 ++++
 doc/coreutils.texi | 17 +++++++++--------
 src/tee.c          |  9 ++-------
 tests/misc/tee.sh  |  7 +++++++
 4 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/NEWS b/NEWS
index b6795aa..8597357 100644
--- a/NEWS
+++ b/NEWS
@@ -73,6 +73,10 @@ GNU coreutils NEWS                                    -*- outline -*-
 
   tee will exit early if there are no more writable outputs.
 
+  tee does not treat the file operand '-' as meaning standard output any longer,
+  for better conformance to POSIX.  This feature was added in coreutils-5.3.0.
+
+
 ** Improvements
 
   cp,install,mv will convert smaller runs of NULs in the input to holes,
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index bb652ac..8d050c2 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -752,11 +752,10 @@ operands even if they begin with @samp{-}.  For example, @samp{sort --
 @cindex standard input
 @cindex standard output
 A single @samp{-} operand is not really an option, though it looks like one.  It
-stands for standard input, or for standard output if that is clear from
-the context.  For example, @samp{sort -} reads from standard input,
-and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
-extra copy of its input to standard output.  Unless otherwise
-specified, @samp{-} can appear as any operand that requires a file
+stands for a file operand, and some tools treat it as standard input, or as
+standard output if that is clear from the context.  For example, @samp{sort -}
+reads from standard input, and is equivalent to plain @samp{sort}.  Unless
+otherwise specified, a @samp{-} can appear as any operand that requires a file
 name.
 
 @menu
@@ -13180,9 +13179,11 @@ If a file being written to does not already exist, it is created.  If a
 file being written to already exists, the data it previously contained
 is overwritten unless the @option{-a} option is used.
 
-A @var{file} of @samp{-} causes @command{tee} to send another copy of
-input to standard output, but this is typically not that useful as the
-copies are interleaved.
+In previous versions of GNU coreutils (v5.3.0 - v8.23), a @var{file} of @samp{-}
+caused @command{tee} to send another copy of input to standard output.
+However, as the interleaved output was not very useful, @command{tee} now
+conforms to POSIX which explicitly mandates it to treat @samp{-} as a file
+with such name.
 
 The program accepts the following options.  Also see @ref{Common options}.
 
diff --git a/src/tee.c b/src/tee.c
index bfe1b69..feb4026 100644
--- a/src/tee.c
+++ b/src/tee.c
@@ -68,10 +68,6 @@ Copy standard input to each FILE, and also to standard output.\n\
 "), stdout);
       fputs (HELP_OPTION_DESCRIPTION, stdout);
       fputs (VERSION_OPTION_DESCRIPTION, stdout);
-      fputs (_("\
-\n\
-If a FILE is -, copy again to standard output.\n\
-"), stdout);
       emit_ancillary_info (PROGRAM_NAME);
     }
   exit (status);
@@ -169,9 +165,8 @@ tee_files (int nfiles, const char **files)
 
   for (i = 1; i <= nfiles; i++)
     {
-      descriptors[i] = (STREQ (files[i], "-")
-                        ? stdout
-                        : fopen (files[i], mode_string));
+      /* Do not treat "-" specially - as mandated by POSIX.  */
+      descriptors[i] = fopen (files[i], mode_string);
       if (descriptors[i] == NULL)
         {
           error (0, errno, "%s", files[i]);
diff --git a/tests/misc/tee.sh b/tests/misc/tee.sh
index 5f2eeda..85597c5 100755
--- a/tests/misc/tee.sh
+++ b/tests/misc/tee.sh
@@ -31,6 +31,13 @@ for n in 0 $nums; do
         done
 done
 
+# Ensure tee treats '-' as the name of a file, as mandated by POSIX.
+# Between v5.3.0 and v8.23, a '-' argument caused tee to send another
+# copy of input to standard output.
+tee - <sample >out 2>err || fail=1
+compare sample ./- || fail=1
+compare sample out || fail=1
+compare /dev/null err || fail
 
 # Ensure tee exits early if no more writable outputs
 if test -w /dev/full && test -c /dev/full; then
-- 
2.1.4