dup, dup2, dup3

Duplicate a file descriptor. These system calls create a copy of the file descriptor oldfd.

SYNOPSIS

#include <unistd.h>
int dup(int oldfd);
int dup2(int oldfd, int newfd);

#define _GNU_SOURCE
#include <unistd.h>
int dup3(int oldfd, int newfd, int flags);

DESCRIPTION

dup() uses the lowest-numbered unused descriptor for the new descriptor.

dup2() makes newfd be the copy of oldfd, closing newfd first if necessary, but note the following:

  • If oldfd is not a valid file descriptor, then the call fails, and newfd is not closed.
  • If oldfd is a valid file descriptor, and newfd has the same value as oldfd, then dup2() does nothing, and returns newfd.

After a successful return from one of these system calls, the old and new file descriptors may be used interchangeably. They refer to the same open file description (see open(2)) and thus share file offset and file status flags; for example, if the file offset is modified by using lseek(2) on one of the descriptors, the offset is also changed for the other.

EXAMPLES

LICENSE

The original copy of this manual page is

  • Copyright © 1992 Drew Eckhardt;
  • Copyright © 1993 Michael Haardt, Ian Jackson.
  • Copyright © 2005, 2008 Michael Kerrisk [email protected]
  • Copyright © 2014 Michael Kerrisk [email protected]

The derived copy presented on this page is

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally.

Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work.

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