DUP(II)                       8/5/73                      DUP(II)



NAME
     dup - duplicate an open file descriptor

SYNOPSIS
     (dup = 41.; not in assembler)
     (file descriptor in r0)
     sys dup

     dup(fildes)
     int fildes;

DESCRIPTION
     Given a file descriptor returned from an open, pipe, or cre-
     at call, dup will allocate another file  descriptor  synony-
     mous with the original.  The new file descriptor is returned
     in r0.

     Dup is used more to reassign the value of  file  descriptors
     than  to  genuinely  duplicate a file descriptor.  Since the
     algorithm to allocate file descriptors  returns  the  lowest
     available  value,  combinations of dup and close can be used
     to manipulate file descriptors in a general  way.   This  is
     handy  for  manipulating standard input and/or standard out-
     put.

SEE ALSO
     creat(II), open(II), close(II), pipe(II)

DIAGNOSTICS
     The error bit (c-bit) is set if: the given  file  descriptor
     is  invalid; there are already too many open files.  From C,
     a -1 returned value indicates an error.

























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