[apple/xnu.git] / bsd / man / man2 / dup.2

.\"	$NetBSD: dup.2,v 1.4 1995/02/27 12:32:21 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)dup.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt DUP 2
.Os BSD 4
.Sh NAME
.Nm dup ,
.Nm dup2
.Nd duplicate an existing file descriptor
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn dup "int oldd"
.Ft int
.Fn dup2 "int oldd" "int newd"
.Sh DESCRIPTION
.Fn Dup
duplicates an existing object descriptor and returns its value to
the calling process
.Fa ( newd
=
.Fn dup oldd ) .
The argument
.Fa oldd
is a small non-negative integer index in
the per-process descriptor table.  The value must be less
than the size of the table, which is returned by
.Xr getdtablesize 2 .
The new descriptor returned by the call
is the lowest numbered descriptor
currently not in use by the process.
.Pp
The object referenced by the descriptor does not distinguish
between
.Fa oldd
and
.Fa newd
in any way.
Thus if
.Fa newd
and
.Fa oldd
are duplicate references to an open
file,
.Xr read 2 ,
.Xr write 2
and
.Xr lseek 2
calls all move a single pointer into the file,
and append mode, non-blocking I/O and asynchronous I/O options
are shared between the references.
If a separate pointer into the file is desired, a different
object reference to the file must be obtained by issuing an
additional
.Xr open 2
call.
The close-on-exec flag on the new file descriptor is unset.
.Pp
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
.Xr close 2
call had been done first.
.Sh RETURN VALUES
The value -1 is returned if an error occurs in either call.
The external variable
.Va errno
indicates the cause of the error.
.Sh ERRORS
.Fn Dup
and
.Fn dup2
fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa Oldd
or
.Fa newd
is not a valid active descriptor
.It Bq Er EMFILE
Too many descriptors are active.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr open 2 ,
.Xr close 2 ,
.Xr fcntl 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 2 ,
.Xr getdtablesize 2
.Sh STANDARDS
.Fn Dup
and
.Fn dup2
are expected to conform to 
.St -p1003.1-88 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: dup.2,v 1.4 1995/02/27 12:32:21 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)dup.2 8.1 (Berkeley) 6/4/93
	35	.\"
	36	.Dd June 4, 1993
	37	.Dt DUP 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm dup ,
	41	.Nm dup2
	42	.Nd duplicate an existing file descriptor
	43	.Sh SYNOPSIS
	44	.Fd #include <unistd.h>
	45	.Ft int
	46	.Fn dup "int oldd"
	47	.Ft int
	48	.Fn dup2 "int oldd" "int newd"
	49	.Sh DESCRIPTION
	50	.Fn Dup
	51	duplicates an existing object descriptor and returns its value to
	52	the calling process
	53	.Fa ( newd
	54	=
	55	.Fn dup oldd ) .
	56	The argument
	57	.Fa oldd
	58	is a small non-negative integer index in
	59	the per-process descriptor table. The value must be less
	60	than the size of the table, which is returned by
	61	.Xr getdtablesize 2 .
	62	The new descriptor returned by the call
	63	is the lowest numbered descriptor
	64	currently not in use by the process.
65	.Pp
66	The object referenced by the descriptor does not distinguish
67	between
68	.Fa oldd
69	and
70	.Fa newd
71	in any way.
72	Thus if
73	.Fa newd
74	and
75	.Fa oldd
76	are duplicate references to an open
77	file,
78	.Xr read 2 ,
79	.Xr write 2
80	and
81	.Xr lseek 2
82	calls all move a single pointer into the file,
83	and append mode, non-blocking I/O and asynchronous I/O options
84	are shared between the references.
85	If a separate pointer into the file is desired, a different
86	object reference to the file must be obtained by issuing an
87	additional
88	.Xr open 2
89	call.
90	The close-on-exec flag on the new file descriptor is unset.
91	.Pp
92	In
93	.Fn dup2 ,
94	the value of the new descriptor
95	.Fa newd
96	is specified. If this descriptor is already
97	in use, the descriptor is first deallocated as if a
98	.Xr close 2
99	call had been done first.
100	.Sh RETURN VALUES
101	The value -1 is returned if an error occurs in either call.
102	The external variable
103	.Va errno
104	indicates the cause of the error.
105	.Sh ERRORS
106	.Fn Dup
107	and
108	.Fn dup2
109	fail if:
110	.Bl -tag -width Er
111	.It Bq Er EBADF
112	.Fa Oldd
113	or
114	.Fa newd
115	is not a valid active descriptor
116	.It Bq Er EMFILE
117	Too many descriptors are active.
118	.El
119	.Sh SEE ALSO
120	.Xr accept 2 ,
121	.Xr open 2 ,
122	.Xr close 2 ,
123	.Xr fcntl 2 ,
124	.Xr pipe 2 ,
125	.Xr socket 2 ,
126	.Xr socketpair 2 ,
127	.Xr getdtablesize 2
128	.Sh STANDARDS
129	.Fn Dup
130	and
131	.Fn dup2
132	are expected to conform to
133	.St -p1003.1-88 .