man.postnix Miscellaneous man pages of Plan 9 related material

     SYS-DUP(2)                                             SYS-DUP(2)

     NAME
          dup, fildes - duplicate an open file descriptor

     SYNOPSIS
          include "sys.m";
          sys := load Sys Sys->PATH;

          dup:    fn(oldfd, newfd: int):  int;
          fildes: fn(fd: int):            ref FD;

     DESCRIPTION
          The Limbo programming language and its libraries manage I/O
          via references to instances of abstract data type, FD,
          called a Limbo file descriptor, or simply `file descriptor'
          when the context is understood.  FD holds an integer-valued
          file descriptor, the form used by the operating system, in a
          structure that can be reference counted and garbage col-
          lected.  There are occasions when a program must access the
          underlying integer file descriptor, such as when rearranging
          the standard input and output for a new subprocess.

          The dup call takes a valid integer file descriptor, oldfd,
          referring to an open file, and returns a new integer file
          descriptor referring to the same file.  If newfd is in the
          range of legal file descriptors, dup will use that for the
          new file descriptor (closing any old file associated with
          newfd); if newfd is -1 the system chooses the lowest avail-
          able file descriptor.  If a suitable file descriptor cannot
          be found, dup returns -1.

          Fildes uses the integer file descriptor fd to create a new
          Limbo file descriptor, suitable for other Sys module func-
          tions.  It returns nil if it cannot convert fd.

     SEE ALSO
          sys-intro(2), sys-open(2)

     Page 1                       Plan 9            (printed 10/29/25)