Description

   This routine allows an application to verify the existence
   of, and return components of, a file specification. Wildcard
   operations are permitted. The routine uses the $PARSE and $SEARCH
   system services to seek the file specification.

   If no wildcards are included in the file specification string
   and the result-string returns a zero (0) length string, no
   file was found. If wildcard characters were present in the file
   specification and the result-string returns a zero (0) length
   string, there are no more files that match the wildcards.

   To find all the files that match a wildcard specification,
   repeatedly call this routine, passing the same arguments, until
   the routine returns a zero-length result string.

   The TPU$FILE_SEARCH routine is called by TPU when the TPU
   built-in procedure FILE_SEARCH is executed from TPU code. The
   return value of the built-in procedure is the string returned in
   the result-string argument.