send — Execute a command in a different application
-displayof pathName


send — Execute a command in a different application


send ?options? app cmd ?arg arg ...?


This command arranges for cmd (and args) to be executed in the application named by app. It returns the result or error from that command execution. App may be the name of any application whose main window is on the display containing the sender's main window; it need not be within the same process. If no arg arguments are present, then the command to be executed is contained entirely within the cmd argument. If one or more args are present, they are concatenated to form the command to be executed, just as for the eval command.

If the initial arguments of the command begin with “-” they are treated as options. The following options are currently defined:

Requests asynchronous invocation. In this case the send command will complete immediately without waiting for cmd to complete in the target application; no result will be available and errors in the sent command will be ignored. If the target application is in the same process as the sending application then the -async option is ignored.
-displayof pathName
Specifies that the target application's main window is on the display of the window given by pathName, instead of the display containing the application's main window.
Serves no purpose except to terminate the list of options. This option is needed only if app could contain a leading “-” character.

Application names

The name of an application is set initially from the name of the program or script that created the application. You can query and change the name of an application with the tk appname command.

Disabling sends

If the send command is removed from an application (e.g. with the command rename send {}) then the application will not respond to incoming send requests anymore, nor will it be able to issue outgoing requests. Communication can be reenabled by invoking the tk appname command.


The send command is potentially a serious security loophole. On Unix, any application that can connect to your X server can send scripts to your applications. These incoming scripts can use Tcl to read and write your files and invoke subprocesses under your name. Host-based access control such as that provided by xhost is particularly insecure, since it allows anyone with an account on particular hosts to connect to your server, and if disabled it allows anyone anywhere to connect to your server. In order to provide at least a small amount of security, Tk checks the access control being used by the server and rejects incoming sends unless (a) xhost-style access control is enabled (i.e. only certain hosts can establish connections) and (b) the list of enabled hosts is empty. This means that applications cannot connect to your server unless they use some other form of authorization such as that provide by xauth. Under Windows, send is currently disabled. Most of the functionality is provided by the dde command instead.


This script fragment can be used to make an application that only runs once on a particular display.
if {[tk appname FoobarApp] ne "FoobarApp"} {
    send -async FoobarApp RemoteStart $argv
# The command that will be called remotely, which raises
# the application main window and opens the requested files
proc RemoteStart args {
    raise .
    foreach filename $args {
        OpenFile $filename

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