This command is part of the [TclX] package.
    :   '''dup''' ''fileId'' ?''targetFileId''?

Duplicate  an open file.  A new file id is opened that addresses the same file as ''fileId''.

If ''targetFileId'' is specified, the the file is dup-ped to this specified  file  id.  Normally this is [stdin], [stdout], or [stderr].  The '''dup''' command will handle flushing output and closing  this  file. The  new  file  will be buffered, if its needs to be unbuffered, use the [fcntl] command to set it unbuffered.

If ''fileId'' is a number rather than a Tcl channel name,  then  the  '''dup''' command  will  bind that file to a Tcl channel.  This is useful for accessing files that are passed  from  the  parent  process. The ''targetFileId'' argument is not valid with this operation.

On [Windows] 95/NT, only [stdin], [stdout], or [stderr] or a non-socket file handle number maybe specified for  ''targetFileId''.   The  '''dup''' command does not work on sockets on Windows 95/NT.



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