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dde(n)                                      Tcl Bundled Packages                                      dde(n)



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NAME
       dde - Execute a Dynamic Data Exchange command

SYNOPSIS
       package require dde 1.3

       dde servername ?-force? ?-handler proc? ?--? ?topic?

       dde execute ?-async? service topic data

       dde poke service topic item data

       dde request ?-binary? service topic item

       dde services service topic

       dde eval ?-async? topic cmd ?arg arg ...?
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DESCRIPTION
       This  command  allows  an  application to send Dynamic Data Exchange (DDE) command when running under
       Microsoft Windows. Dynamic Data Exchange is a mechanism where applications  can  exchange  raw  data.
       Each  DDE  transaction needs a service name and a topic. Both the service name and topic are applica-tion application
       tion defined; Tcl uses the service name TclEval, while the topic name is the name of the  interpreter
       given  by  dde  servername. Other applications have their own service names and topics. For instance,
       Microsoft Excel has the service name Excel.


DDE COMMANDS
       The following commands are a subset of the full Dynamic Data Exchange set of commands.

       dde servername ?-force? ?-handler proc? ?--? ?topic?
              dde servername registers the interpreter as a DDE server with the service name TclEval and the
              topic  name  specified by topic.  If no topic is given, dde servername returns the name of the
              current topic or the empty string if it is not registered as a service.  If  the  given  topic
              name  is  already  in use, then a suffix of the form " #2" or " #3" is appended to the name to
              make it unique. The command's result will be the name actually used. The -force option is used
              to force registration of precisely the given topic name.

              The  -handler option specifies a Tcl procedure that will be called to process calls to the dde
              server. If the package has been loaded into a safe interpreter then a -handler procedure  must
              be defined. The procedure is called with all the arguments provided by the remote call.

       dde execute ?-async? service topic data
              dde  execute  takes  the  data  and sends it to the server indicated by service with the topic
              indicated by topic. Typically, service is the name of an application, and topic is a  file  to
              work  on.   The  data  field  is  given to the remote application.  Typically, the application
              treats the data field as a script, and the script is  run  in  the  application.   The  -async
              option  requests  asynchronous invocation.  The command returns an error message if the script
              did not run, unless the -async flag was used, in which case the  command  returns  immediately
              with no error.

       dde poke service topic item data
              dde  poke  passes  the data to the server indicated by service using the topic and item speci-fied. specified.
              fied.  Typically, service is the name of an application.  topic is  application  specific  but
              can be a command to the server or the name of a file to work on.  The item is also application
              specific and is often not used, but it must always be non-null.  The data field  is  given  to
              the remote application.

       dde request ?-binary? service topic item
              dde  request is typically used to get the value of something; the value of a cell in Microsoft
              Excel or the text of a selection in Microsoft Word. service is typically the name of an appli-cation, application,
              cation, topic is typically the name of the file, and item is application-specific. The command
              returns the value of item as defined in the application.  Normally this is interpreted to be a
              string  with  terminating  null.   If  -binary  is specified, the result is returned as a byte
              array.

       dde services service topic
              dde services returns a list of service-topic pairs that currently exist  on  the  machine.  If
              service  and  topic are both empty strings ({}), then all service-topic pairs currently avail-able available
              able on the system are returned. If service is empty and topic is not, then all services  with
              the specified topic are returned. If service is non-empty and topic is, all topics for a given
              service are returned. If both are non-empty, if that service-topic pair currently  exists,  it
              is returned; otherwise, an empty string is returned.

       dde eval ?-async? topic cmd ?arg arg ...?
              dde  eval  evaluates a command and its arguments using the interpreter specified by topic. The
              DDE service must be the TclEval service.  The -async option requests asynchronous  invocation.
              The  command  returns  an  error message if the script did not run, unless the -async flag was
              used, in which case the command returns immediately with no error.  This command can  be  used
              to replace send on Windows.

DDE AND TCL
       A  Tcl  interpreter  always has a service name of TclEval.  Each different interpreter of all running
       Tcl applications must be given a unique name specified by dde servername. Each interp is available as
       a DDE topic only if the dde servername command was used to set the name of the topic for each interp.
       So a dde services TclEval {} command will return a list of service-topic pairs,  where  each  of  the
       currently running interps will be a topic.

       When  Tcl  processes a dde execute command, the data for the execute is run as a script in the interp
       named by the topic of the dde execute command.

       When Tcl processes a dde request command, it returns the value of the variable given in the dde  com-mand command
       mand  in  the  context  of the interp named by the dde topic. Tcl reserves the variable $TCLEVAL$EXE-CUTE$RESULT $TCLEVAL$EXECUTE$RESULT
       CUTE$RESULT for internal use, and dde request commands for  that  variable  will  give  unpredictable
       results.

       An  external application which wishes to run a script in Tcl should have that script store its result
       in a variable, run the dde execute command, and the run dde request to get the value of the variable.

       When  using  DDE,  be careful to ensure that the event queue is flushed using either update or vwait.
       This happens by default when using wish unless a blocking command is called  (such  as  exec  without
       adding  the  &  to  place  the  process in the background).  If for any reason the event queue is not
       flushed, DDE commands may hang until the event queue is flushed.  This can create a  deadlock  situa-tion. situation.
       tion.

EXAMPLE
       This  asks  Internet  Explorer (which must already be running) to go to a particularly important web-site: website:
       site:
              package require dde
              dde execute iexplore WWW_OpenURL http://www.tcl.tk/

SEE ALSO
       tk(n), winfo(n), send(n)

KEYWORDS
       application, dde, name, remote execution



dde                                                  1.3                                              dde(n)