BSD 4_3_Tahoe development

[unix-history] / usr / man / cat2 / dup.0

DUP(2)		    UNIX Programmer's Manual		   DUP(2)



N\bNA\bAM\bME\bE
     dup, dup2 - duplicate a descriptor

S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
     n\bne\bew\bwd\bd =\b= d\bdu\bup\bp(\b(o\bol\bld\bdd\bd)\b)
     i\bin\bnt\bt n\bne\bew\bwd\bd,\b, o\bol\bld\bdd\bd;\b;

     d\bdu\bup\bp2\b2(\b(o\bol\bld\bdd\bd,\b, n\bne\bew\bwd\bd)\b)
     i\bin\bnt\bt o\bol\bld\bdd\bd,\b, n\bne\bew\bwd\bd;\b;

D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
     _\bD_\bu_\bp duplicates an existing object descriptor.  The argument
     _\bo_\bl_\bd_\bd is a small non-negative integer index in the per-
     process descriptor table.	The value must be less than the
     size of the table, which is returned by _\bg_\be_\bt_\bd_\bt_\ba_\bb_\bl_\be_\bs_\bi_\bz_\be(2).
     The new descriptor returned by the call, _\bn_\be_\bw_\bd, is the lowest
     numbered descriptor that is not currently in use by the pro-
     cess.

     The object referenced by the descriptor does not distinguish
     between references using _\bo_\bl_\bd_\bd and _\bn_\be_\bw_\bd in any way.  Thus if
     _\bn_\be_\bw_\bd and _\bo_\bl_\bd_\bd are duplicate references to an open file,
     _\br_\be_\ba_\bd(2), _\bw_\br_\bi_\bt_\be(2) and _\bl_\bs_\be_\be_\bk(2) calls all move a single
     pointer into the file, and append mode, non-blocking I/O and
     asynchronous I/O options are shared between the references.
     If a separate pointer into the file is desired, a different
     object reference to the file must be obtained by issuing an
     additional _\bo_\bp_\be_\bn(2) call.  The close-on-exec flag on the new
     file descriptor is unset.

     In the second form of the call, the value of _\bn_\be_\bw_\bd desired is
     specified.  If this descriptor is already in use, the
     descriptor is first deallocated as if a _\bc_\bl_\bo_\bs_\be(2) call had
     been done first.

R\bRE\bET\bTU\bUR\bRN\bN V\bVA\bAL\bLU\bUE\bE
     The value -1 is returned if an error occurs in either call.
     The external variable _\be_\br_\br_\bn_\bo indicates the cause of the
     error.

E\bER\bRR\bRO\bOR\bRS\bS
     _\bD_\bu_\bp and _\bd_\bu_\bp_\b2 fail if:

     [EBADF]	    _\bO_\bl_\bd_\bd or _\bn_\be_\bw_\bd is not a valid active descriptor

     [EMFILE]	    Too many descriptors are active.

S\bSE\bEE\bE A\bAL\bLS\bSO\bO
     accept(2), open(2), close(2), fcntl(2), pipe(2), socket(2),
     socketpair(2), getdtablesize(2)





Printed 7/9/88		  May 13, 1986				1