mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-20 11:11:24 +00:00
163 lines
3.9 KiB
Groff
163 lines
3.9 KiB
Groff
.\" 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.
|
|
.\" 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
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd June 4, 1993
|
|
.Dt DUP 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm dup ,
|
|
.Nm dup2
|
|
.Nd duplicate an existing file descriptor
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In unistd.h
|
|
.Ft int
|
|
.Fn dup "int oldd"
|
|
.Ft int
|
|
.Fn dup2 "int oldd" "int newd"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn dup
|
|
system call
|
|
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
|
|
system 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 and
|
|
.Fa oldd
|
|
\*(Ne
|
|
.Fa newd ,
|
|
the descriptor is first deallocated as if the
|
|
.Xr close 2
|
|
system 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 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
|
|
The
|
|
.Fn dup
|
|
and
|
|
.Fn dup2
|
|
system calls fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EBADF
|
|
The
|
|
.Fa oldd
|
|
or
|
|
.Fa newd
|
|
argument
|
|
is not a valid active descriptor
|
|
.It Bq Er EMFILE
|
|
Too many 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
|
|
The
|
|
.Fn dup
|
|
and
|
|
.Fn dup2
|
|
system calls are expected to conform to
|
|
.St -p1003.1-90 .
|
|
.Sh HISTORY
|
|
The
|
|
.Fn dup
|
|
and
|
|
.Fn dup2
|
|
functions appeared in
|
|
.At v7 .
|