DUP (2)
duplicate a file descriptor
SYNOPSIS
#include <unistd.h>
int dup(int oldfd );
int dup2(int oldfd , int newfd );
DESCRIPTION
dup and dup2
create a copy of the file descriptor
oldfd .
After successful return of dup or dup2,
the old and new descriptors may be used interchangeably. They share
locks, file position pointers and flags; for example, if the file
position is modified by using
lseek
on one of the descriptors, the position is also changed for the other.
The two descriptors do not share the close-on-exec flag, however.
dup
uses the lowest-numbered unused descriptor for the new descriptor.
dup2
makes newfd be the copy of oldfd , closing newfd
first if necessary.
RETURN VALUE
dup and dup2
return the new descriptor, or -1 if an error occurred (in which case,
errno
is set appropriately).
ERRORS
EBADF
oldfd
isn't an open file descriptor, or
newfd
is out of the allowed range for file descriptors.
EMFILE
The process already has the maximum number of file
descriptors open and tried to open a new one.
WARNING
The error returned by
dup2
is different to that returned by
fcntl( ..., F_DUPFD , ... )
when
newfd
is out of range. On some systems
dup2
also sometimes returns
EINVAL
like
F_DUPFD .
CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4 documents additional
EINTR and ENOLINK error conditions. POSIX.1 adds EINTR.
SEE ALSO
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