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 creat call, dup will allocate another file descriptor synonymous 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 between 0 and 9, 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 output. 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 10 open files. From C, a -1 returned value indicates an error.