Provided by: tcl8.4-doc_8.4.20-8_all 
NAME
dde - Execute a Dynamic Data Exchange command
SYNOPSIS
package require dde 1.2
dde eval ?-async? service cmd ?arg ...?
dde execute ?-async? service topic data
dde poke service topic item data
dde request ?-binary? service topic data
dde servername ?topic?
dde services service topic
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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.
The eval and execute commands accept the option -async:
DDE COMMANDS
The following commands are a subset of the full Dynamic Data Exchange set of commands.
dde servername ?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.
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 null strings ({}), then all service-topic
pairs currently available on the system are returned. If service is null and topic
is not, then all services with the specified topic are returned. If service is not
null and topic is, all topics for a given service are returned. If both are not
null, if that service-topic pair currently exists, it is returned; otherwise, null
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