[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
.Fo dup
.Fa "int fildes"
.Fc
.Ft int
.Fo dup2
.Fa "int fildes"
.Fa "int fildes2"
.Fc
.Sh DESCRIPTION
.Fn Dup
duplicates an existing object descriptor
and returns its value to the calling process
.Fa ( fildes2
=
.Fn dup fildes ) .
The argument
.Fa fildes
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 fildes
and
.Fa fildes2
in any way.
Thus if
.Fa fildes2
and
.Fa fildes
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 fildes2
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
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and the global integer variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn dup
and
.Fn dup2
system calls will fail if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EBADF
.Fa fildes
or
.Fa fildes2
is not an active, valid file descriptor.
.\" ==========
.It Bq Er EINTR
Execution is interrupted by a signal.
.\" ==========
.It Bq Er EMFILE
Too many file descriptors are active.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr close 2 ,
.Xr fcntl 2 ,
.Xr getdtablesize 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 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
2d21ac55 A	46	.Fo dup
	47	.Fa "int fildes"
	48	.Fc
9bccf70c	49	.Ft int
2d21ac55 A	50	.Fo dup2
	51	.Fa "int fildes"
	52	.Fa "int fildes2"
	53	.Fc
9bccf70c A	54	.Sh DESCRIPTION
9bccf70c A	55	.Fn Dup
2d21ac55 A	56	duplicates an existing object descriptor
	57	and returns its value to the calling process
	58	.Fa ( fildes2
9bccf70c	59	=
2d21ac55	60	.Fn dup fildes ) .
9bccf70c	61	The argument
2d21ac55 A	62	.Fa fildes
	63	is a small non-negative integer index
	64	in the per-process descriptor table.
	65	The value must be less than the size of the table,
	66	which is returned by
9bccf70c A	67	.Xr getdtablesize 2 .
	68	The new descriptor returned by the call
	69	is the lowest numbered descriptor
	70	currently not in use by the process.
	71	.Pp
	72	The object referenced by the descriptor does not distinguish
	73	between
2d21ac55	74	.Fa fildes
9bccf70c	75	and
2d21ac55	76	.Fa fildes2
9bccf70c A	77	in any way.
9bccf70c A	78	Thus if
2d21ac55	79	.Fa fildes2
9bccf70c	80	and
2d21ac55	81	.Fa fildes
9bccf70c A	82	are duplicate references to an open
	83	file,
	84	.Xr read 2 ,
	85	.Xr write 2
	86	and
	87	.Xr lseek 2
	88	calls all move a single pointer into the file,
	89	and append mode, non-blocking I/O and asynchronous I/O options
	90	are shared between the references.
2d21ac55 A	91	If a separate pointer into the file is desired,
	92	a different object reference to the file must be obtained
	93	by issuing an additional
9bccf70c A	94	.Xr open 2
	95	call.
	96	The close-on-exec flag on the new file descriptor is unset.
	97	.Pp
	98	In
	99	.Fn dup2 ,
	100	the value of the new descriptor
2d21ac55 A	101	.Fa fildes2
	102	is specified.
	103	If this descriptor is already in use,
	104	the descriptor is first deallocated as if a
9bccf70c A	105	.Xr close 2
	106	call had been done first.
	107	.Sh RETURN VALUES
2d21ac55 A	108	Upon successful completion, a value of 0 is returned.
2d21ac55 A	109	Otherwise, a value of -1 is returned and the global integer variable
9bccf70c	110	.Va errno
2d21ac55	111	is set to indicate the error.
9bccf70c	112	.Sh ERRORS
2d21ac55 A	113	The
2d21ac55 A	114	.Fn dup
9bccf70c A	115	and
9bccf70c A	116	.Fn dup2
2d21ac55	117	system calls will fail if:
9bccf70c	118	.Bl -tag -width Er
2d21ac55	119	.\" ==========
9bccf70c	120	.It Bq Er EBADF
2d21ac55	121	.Fa fildes
9bccf70c	122	or
2d21ac55 A	123	.Fa fildes2
	124	is not an active, valid file descriptor.
	125	.\" ==========
	126	.It Bq Er EINTR
	127	Execution is interrupted by a signal.
	128	.\" ==========
9bccf70c	129	.It Bq Er EMFILE
2d21ac55	130	Too many file descriptors are active.
9bccf70c A	131	.El
	132	.Sh SEE ALSO
	133	.Xr accept 2 ,
9bccf70c A	134	.Xr close 2 ,
9bccf70c A	135	.Xr fcntl 2 ,
2d21ac55 A	136	.Xr getdtablesize 2 ,
2d21ac55 A	137	.Xr open 2 ,
9bccf70c A	138	.Xr pipe 2 ,
9bccf70c A	139	.Xr socket 2 ,
2d21ac55	140	.Xr socketpair 2
9bccf70c A	141	.Sh STANDARDS
	142	.Fn Dup
	143	and
	144	.Fn dup2
	145	are expected to conform to
	146	.St -p1003.1-88 .