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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
     creat call, dup will allocate another file descriptor syn-
     onymous 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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