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DUP(3)                     Library Functions Manual                     DUP(3)



NAME
       dup - dups of open files

SYNOPSIS
       bind #d /fd

       /fd/0
       /fd/0ctl
       /fd/1
       /fd/1ctl
       ...

DESCRIPTION
       The  dup  device  serves  a  one-level directory containing files whose
       names are decimal numbers.  Each such file also has an associated  con‐
       trol  file.   A file of name n corresponds to open file descriptor n in
       the current process.

       An open(2) of file n results in a file  descriptor  identical  to  what
       would  be returned from a system call dup(n, -1).  Note that the result
       is no longer a file in the dup device.

       The stat operation returns information about the device file,  not  the
       open  file it points to.  A stat of #d/n will contain n for the name, 0
       for the length, and 0400, 0200, or 0600  for  the  mode,  depending  on
       whether the dup target is open for reading, writing, or both.

       A file of name nctl may be read to discover the properties of the asso‐
       ciated file descriptor, in format identical to that of the fd  file  in
       proc(3).

SEE ALSO
       dup(2)

SOURCE
       /sys/src/9/port/devdup.c



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