mirror of
https://github.com/GnoConsortium/gno.git
synced 2024-11-01 02:04:32 +00:00
130 lines
3.8 KiB
Groff
130 lines
3.8 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.
|
|
.\" 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
|
|
.\"
|
|
.TH DUP 2 "16 January 1997" GNO "System Calls"
|
|
.SH NAME
|
|
.BR dup ,
|
|
.BR dup2
|
|
\- duplicate an existing file descriptor
|
|
.SH SYNOPSIS
|
|
.br
|
|
#include <unistd.h>
|
|
.sp 1
|
|
int
|
|
\fBdup\fR (int \fIoldfd\fR);
|
|
.br
|
|
int
|
|
\fBdup2\fR (int \fIoldfd\fR, int \fInewfd\fR);
|
|
.SH DESCRIPTION
|
|
.BR Dup
|
|
duplicates an existing file descriptor and returns its value to
|
|
the calling process.
|
|
The argument
|
|
.I oldfd
|
|
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
|
|
.BR getdtablesize (2).
|
|
The new descriptor returned by the call
|
|
is the lowest numbered descriptor
|
|
currently not in use by the process.
|
|
.LP
|
|
The file referenced by the descriptor does not distinguish
|
|
between
|
|
.I oldfd
|
|
and
|
|
.I newfd
|
|
in any way.
|
|
Thus if
|
|
.I newfd
|
|
and
|
|
.I oldfd
|
|
are duplicate references to an open
|
|
file,
|
|
.BR read (2),
|
|
.BR write (2)
|
|
and
|
|
.BR 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
|
|
reference to the file must be obtained by issuing an
|
|
additional
|
|
.BR open (2)
|
|
call.
|
|
The close-on-exec flag on the new file descriptor is unset.
|
|
.LP
|
|
In
|
|
.BR dup2 ,
|
|
the value of the new descriptor
|
|
.I newfd
|
|
is specified. If this descriptor is already
|
|
in use, the descriptor is first deallocated as if a
|
|
.BR 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
|
|
.IR errno
|
|
indicates the cause of the error.
|
|
.SH ERRORS
|
|
.BR Dup
|
|
and
|
|
.BR dup2
|
|
fail if:
|
|
.RS
|
|
.IP \fBEBADF\fR
|
|
.I Oldfd
|
|
or
|
|
.I newfd
|
|
is not a valid active descriptor
|
|
.IP \fBEMFILE\fR
|
|
Too many descriptors are active.
|
|
.RE
|
|
.SH SEE ALSO
|
|
.BR accept (2),
|
|
.BR open (2),
|
|
.BR close (2),
|
|
.BR fcntl (2),
|
|
.BR pipe (2),
|
|
.BR socket (2),
|
|
.BR socketpair (2),
|
|
.BR getdtablesize (2)
|
|
.SH STANDARDS
|
|
.BR Dup
|
|
and
|
|
.BR dup2
|
|
are expected to conform
|
|
to IEEE Std 1003.1-1988 (POSIX).
|