Provided by: tcl8.5-doc_8.5.19-4_all 
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 application
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 specified.
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
application, 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 available 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 command
in the context of the interp named by the dde topic. Tcl reserves the variable $TCLEVAL$EXECUTE$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 then 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 situation.
EXAMPLE
This asks Internet Explorer (which must already be running) to go to a particularly important website:
package require dde
dde execute -async iexplore WWW_OpenURL http://www.tcl.tk/
SEE ALSO
tk(3tk), winfo(3tk), send(3tk)
KEYWORDS
application, dde, name, remote execution