mirror of https://github.com/GnoConsortium/gno.git
130 lines
3.8 KiB
Groff
130 lines
3.8 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)dup.2 8.1 (Berkeley) 6/4/93
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.\"
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.TH DUP 2 "16 January 1997" GNO "System Calls"
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.SH NAME
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.BR dup ,
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.BR dup2
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\- duplicate an existing file descriptor
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.SH SYNOPSIS
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.br
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#include <unistd.h>
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.sp 1
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int
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\fBdup\fR (int \fIoldfd\fR);
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.br
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int
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\fBdup2\fR (int \fIoldfd\fR, int \fInewfd\fR);
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.SH DESCRIPTION
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.BR Dup
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duplicates an existing file descriptor and returns its value to
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the calling process.
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The argument
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.I oldfd
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is a small non-negative integer index in
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the per-process descriptor table. The value must be less
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than the size of the table, which is returned by
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.BR getdtablesize (2).
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The new descriptor returned by the call
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is the lowest numbered descriptor
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currently not in use by the process.
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.LP
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The file referenced by the descriptor does not distinguish
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between
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.I oldfd
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and
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.I newfd
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in any way.
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Thus if
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.I newfd
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and
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.I oldfd
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are duplicate references to an open
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file,
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.BR read (2),
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.BR write (2)
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and
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.BR lseek (2)
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calls all move a single pointer into the file,
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and append mode, non-blocking I/O and asynchronous I/O options
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are shared between the references.
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If a separate pointer into the file is desired, a different
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reference to the file must be obtained by issuing an
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additional
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.BR open (2)
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call.
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The close-on-exec flag on the new file descriptor is unset.
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.LP
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In
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.BR dup2 ,
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the value of the new descriptor
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.I newfd
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is specified. If this descriptor is already
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in use, the descriptor is first deallocated as if a
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.BR close (2)
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call had been done first.
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.SH RETURN VALUES
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The value -1 is returned if an error occurs in either call.
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The external variable
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.IR errno
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indicates the cause of the error.
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.SH ERRORS
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.BR Dup
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and
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.BR dup2
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fail if:
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.RS
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.IP \fBEBADF\fR
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.I Oldfd
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or
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.I newfd
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is not a valid active descriptor
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.IP \fBEMFILE\fR
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Too many descriptors are active.
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.RE
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.SH SEE ALSO
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.BR accept (2),
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.BR open (2),
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.BR close (2),
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.BR fcntl (2),
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.BR pipe (2),
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.BR socket (2),
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.BR socketpair (2),
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.BR getdtablesize (2)
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.SH STANDARDS
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.BR Dup
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and
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.BR dup2
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are expected to conform
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to IEEE Std 1003.1-1988 (POSIX).
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