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.Dd August 16, 2013 .Dt DUP3 3 .Os .Sh NAME .Nm dup3 .Nd duplicate an existing file descriptor .Sh LIBRARY .Lb libc .Sh SYNOPSIS n fcntl.h n unistd.h .Ft int .Fn dup3 "int oldd" "int newd" "int flags" .Sh DESCRIPTION The .Fn dup3 function duplicates an existing object descriptor while allowing the value of the new descriptor to be specified.
p The close-on-exec flag on the new file descriptor is determined by the .Dv O_CLOEXEC bit in .Fa flags .
p If .Fa oldd \*(Ne .Fa newd and .Fa flags == 0, the behavior is identical to .Li dup2(oldd, newd) .
p If .Fa oldd == .Fa newd , then .Fn dup3 fails, unlike .Xr dup2 2 . .Sh RETURN VALUES The value -1 is returned if an error occurs. The external variable .Va errno indicates the cause of the error. .Sh ERRORS The .Fn dup3 function fails if: l -tag -width Er t Bq Er EBADF The .Fa oldd argument is not a valid active descriptor or the .Fa newd argument is negative or exceeds the maximum allowable descriptor number t Bq Er EINVAL The .Fa oldd argument is equal to the .Fa newd argument. t Bq Er EINVAL The .Fa flags argument has bits set other than .Dv O_CLOEXEC . .El .Sh SEE ALSO .Xr accept 2 , .Xr close 2 , .Xr dup2 2 , .Xr fcntl 2 , .Xr getdtablesize 2 , .Xr open 2 , .Xr pipe 2 , .Xr socket 2 , .Xr socketpair 2 .Sh STANDARDS The .Fn dup3 function does not conform to any standard. .Sh HISTORY The .Fn dup3 function appeared in .Fx 10.0 .