Tcl_GetOpenFile  -  Get a standard IO File * handle from a
       channel. (Unix only)


       #include <tcl.h>

       Tcl_GetOpenFile(interp, string, write, checkUsage, filePtr)


       Tcl_Interp   *interp      (in)      Tcl  interpreter  from
                                           which  file  handle is
                                           to be obtained.

       char         *string      (in)      String     identifying
                                           channel, such as stdin
                                           or file4.

       int          write        (in)      Non-zero   means   the
                                           file  will be used for
                                           writing, zero means it
                                           will be used for read­

       int          checkUsage   (in)      If non-zero,  then  an
                                           error  will  be gener­
                                           ated   if   the   file
                                           wasn't  opened for the
                                           access  indicated   by

       ClientData   *filePtr     (out)     Points   to   word  in
                                           which to store pointer
                                           to  FILE structure for
                                           the  file   given   by


       Tcl_GetOpenFile takes as argument a file identifier of the
       form returned by the open command and returns at  *filePtr
       a  pointer  to the FILE structure for the file.  The write
       argument indicates whether the FILE pointer will  be  used
       for  reading or writing.  In some cases, such as a channel
       that connects to a  pipeline  of  subprocesses,  different
       FILE  pointers  will  be returned for reading and writing.
       Tcl_GetOpenFile normally  returns  TCL_OK.   If  an  error
       occurs  in  Tcl_GetOpenFile  (e.g.  string didn't make any
       and the interpreter's result will contain  an  error  mes­
       sage.  In the current implementation checkUsage is ignored
       and consistency checks are always performed.               |

       Note that this interface is only  supported  on  the  Unix |


       channel, file handle, permissions, pipeline, read, write