send(3) User Contributed Perl Documentation send(3)
NAME
Tk::send - Execute a command in a different application
SYNOPSIS
$result = $widget->send(?options,?app=>cmd?arg arg ...?)
DESCRIPTION
This method arranges for cmd (and args) to be 'sent' to the application
named by app. It returns the result or an error (hence above should
probably be 'wrapped' in eval{} and $@ tested). 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 string to be sent is contained
entirely within the cmd argument. If one or more args are present,
they are concatenated separated by white space to form the string to be
sent.
If the initial arguments of the call begin with ``-'' they are treated
as options. The following options are currently defined:
-async
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.
-- 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 appname method.
WHAT IS A SEND
The send mechanism was designed to allow Tcl/Tk applications to send
Tcl Scripts to each other. This does not map very well onto perl/Tk.
Perl/Tk "sends" a string to app, what happens as a result of this
depends on the receiving application. If the other application is a
Tcl/Tk4.* application it will be treated as a Tcl Script. If the
"other" application is perl/Tk application (including sends to self)
then the string is passed as an argument to a method call of the
following form:
$mainwindow->Receive(string);
There is a default (AutoLoaded) Tk::Receive which returns an error to
the sending application. A particular application may define its own
Receive method in any class in MainWindow's inheritance tree to do
whatever it sees fit. For example it could eval the string, possibly in
a Safe "compartment".
If a Tcl/Tk application "sends" anything to a perl/Tk application then
the perl/Tk application would have to attempt to interpret the incoming
string as a Tcl Script. Simple cases are should not be too hard to
emulate (split on white space and treat first element as "command" and
other elements as arguments).
SECURITY
The send command is potentially a serious security loophole, since any
application that can connect to your X server can send scripts to your
applications. Hence the default behaviour outlined above. (With the
availability of Safe it may make sense to relax default behaviour a
little.)
Unmonitored eval'ing of these incoming "scripts" can cause perl to read
and write 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,
core 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.
SEE ALSO
"eval" in perlfunc, Safe, system's administrator/corporate security
guidelines etc.
KEYWORDS
application, name, remote execution, security, send
perl v5.18.0 2012-11-12 send(3)
perl-Tk 804.030_502 - Generated Sat Aug 17 19:21:53 CDT 2013