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    Command:

    dup

    
    
    

    SYNOPSIS

           #include <unistd.h>
    
           int dup(int oldfd);
           int dup2(int oldfd, int newfd);
    
           #define _GNU_SOURCE             /* See feature_test_macros(7) */
           #include <fcntl.h>              /* Obtain O_* constant definitions */
           #include <unistd.h>
    
           int dup3(int oldfd, int newfd, int flags);
    
    
    

    DESCRIPTION

           These system calls create a copy of the file descriptor oldfd.
    
           dup()  uses  the lowest-numbered unused descriptor for the new descrip-
           tor.
    
           dup2() makes newfd be the copy of oldfd, closing newfd first if  neces-
           sary, 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.
    
           The two descriptors do not share file descriptor flags  (the  close-on-
           exec  flag).  The close-on-exec flag (FD_CLOEXEC; see fcntl(2)) for the
           duplicate descriptor is off.
    
           dup3() is the same as dup2(), except that:
    
           *  The caller can force the close-on-exec flag to be set  for  the  new
              file  descriptor by specifying O_CLOEXEC in flags.  See the descrip-
              tion of the same flag in open(2) for reasons why this may be useful.
    
           *  If oldfd equals newfd, then dup3() fails with the error EINVAL.
    
    
    

    RETURN VALUE

           On success, these system calls return the new descriptor.  On error, -1
           is returned, and errno is set appropriately.
    
    
    

    ERRORS

           EBADF  oldfd isn't an open file descriptor, or  newfd  is  out  of  the
    
    
    

    VERSIONS

           dup3() was added to Linux in version 2.6.27; glibc support is available
           starting with version 2.9.
    
    
    

    CONFORMING TO

           dup(), dup2(): SVr4, 4.3BSD, POSIX.1-2001.
    
           dup3() is Linux-specific.
    
    
    

    NOTES

           The error returned  by  dup2()  is  different  from  that  returned  by
           fcntl(...,  F_DUPFD, ...)  when newfd is out of range.  On some systems
           dup2() also sometimes returns EINVAL like F_DUPFD.
    
           If newfd was open, any errors that would have been reported at close(2)
           time  are  lost.   A  careful  programmer will not use dup2() or dup3()
           without closing newfd first.
    
    
    

    SEE ALSO

           close(2), fcntl(2), open(2)
    
    
    

    Linux 2012-02-14 DUP(2)

    
    
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