From ac225cf76dfd6293ef024bdd2a3a7a24787bacb3 Mon Sep 17 00:00:00 2001
From: Stephen McKay <mckay@FreeBSD.org>
Date: Sun, 9 Mar 1997 13:16:48 +0000
Subject: Clarified the behaviour of dup2(fd1,fd2) when fd1==fd2 and when fd1
 is invalid.

Safe for 2.2!
---
 lib/libc/sys/dup.2 | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

(limited to 'lib')

diff --git a/lib/libc/sys/dup.2 b/lib/libc/sys/dup.2
index 66c9d29728c54..58a967d22e015 100644
--- a/lib/libc/sys/dup.2
+++ b/lib/libc/sys/dup.2
@@ -30,7 +30,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     @(#)dup.2	8.1 (Berkeley) 6/4/93
-.\"	$Id$
+.\"	$Id: dup.2,v 1.7 1997/02/22 15:03:49 peter Exp $
 .\"
 .Dd June 4, 1993
 .Dt DUP 2
@@ -92,10 +92,27 @@ In
 .Fn dup2 ,
 the value of the new descriptor
 .Fa newd
-is specified.  If this descriptor is already
-in use, the descriptor is first deallocated as if a
+is specified.  If this descriptor is already in use and
+.Fa oldd
+!=
+.Fa newd ,
+the descriptor is first deallocated as if a
 .Xr close 2
-call had been done first.
+call had been used.
+If
+.Fa oldd
+is not a valid descriptor, then
+.Fa newd
+is not closed.
+If
+.Fa oldd
+==
+.Fa newd
+and
+.Fa oldd
+is a valid descriptor, then
+.Fn dup2
+is successful, and does nothing.
 .Sh IMPLEMENTATION NOTES
 .Pp
 In the non-threaded library
-- 
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