source fileName
      Read file fileName and pass the contents to the Tcl
      interpreter as a sequence of commands to execute in the
      normal fashion. The return value of source is the
      return value of the last command executed from the
      file.  If an error occurs in executing the contents of
      the file, then the source command will return that
      error.  If a return command is invoked from within the
      file, the remainder of the file will be skipped and the
      source command will return normally with the result
      from the return command.