NAME
dup2 — duplicate an open file descriptor to a specific slot
SYNOPSIS
#include <unistd.h>
int dup2(int fildes, int fildes2);
DESCRIPTION
fildes
is a file descriptor obtained from a
creat(),
open(),
dup(),
fcntl(),
or
pipe()
system call.
fildes2
is a non-negative integer less than the maximum value
allowed for file descriptors.
dup2()
causes
fildes2
to refer to the same file as
fildes.
If
fildes2
refers to an already open file, the open file is closed first.
The file descriptor returned by
dup2()
has the following in common with
fildes:
Same open file (or pipe).
Same file pointer (that is, both file descriptors share one file pointer.)
Same access mode (read, write or read/write).
Same file status flags (see
fcntl(2),
F_DUPFD).
The new file descriptor is set to remain open across
exec()
system calls.
See
fcntl(2).
This routine is found in the C library.
Programs using
dup2()
but not using other routines from the Berkeley importability library
(such as the routines described in
bsdproc(3C))
should not give the
-lBSD
option to
ld(1).
RETURN VALUE
Upon successful completion,
dup2()
returns the new file descriptor as a non-negative integer,
fildes2.
Otherwise, it returns -1 and sets
errno
to indicate the error.
ERRORS
dup2()
fails if the following is true:
- [EBADF]
fildes
is not a valid open file descriptor or
fildes2
is not in the range of legal file descriptors.
- [EINTR]
An attempt to close
fildes2
was interrupted by a signal.
The file is still open.
STANDARDS CONFORMANCE
dup2(): AES, SVID2, SVID3, XPG3, XPG4, FIPS 151-2, POSIX.1
