path: root/doc/selection.n

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.TH selection n 8.1 Tk "Tk Built-In Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
selection \- Manipulate the X selection
.SH SYNOPSIS
\fBselection \fIoption\fR ?\fIarg ...\fR?
.BE
.SH DESCRIPTION
.PP
This command provides a Tcl interface to the X selection mechanism and
implements the full selection functionality described in the
X Inter-Client Communication Conventions Manual (ICCCM).
.PP
Note that for management of the \fBCLIPBOARD\fR selection (see below), the
\fBclipboard\fR command may also be used.
.PP
The first argument to \fBselection\fR determines the format of the
rest of the arguments and the behavior of the command.  The following
forms are currently supported:
.\" METHOD: clear
.TP
\fBselection clear\fR ?\fB\-displayof\fI window\fR? ?\fB\-selection\fI selection\fR?
.
If \fIselection\fR exists anywhere on \fIwindow\fR's display, clear it
so that no window owns the selection anymore.  \fISelection\fR
specifies the X selection that should be cleared, and should be an
atom name such as \fBPRIMARY\fR or \fBCLIPBOARD\fR; see the Inter-Client
Communication Conventions Manual for complete details.
\fISelection\fR defaults to \fBPRIMARY\fR and \fIwindow\fR defaults to
.QW . .
Returns an empty string.
.\" METHOD: get
.TP
\fBselection get\fR ?\fB\-displayof\fI window\fR? ?\fB\-selection\fI selection\fR? ?\fB\-type\fI type\fR?
.
Retrieves the value of \fIselection\fR from \fIwindow\fR's display and
returns it as a result.  \fISelection\fR defaults to \fBPRIMARY\fR and
\fIwindow\fR defaults to
.QW . .
\fIType\fR specifies the form in which the selection is to be returned
(the desired
.QW target
for conversion, in ICCCM terminology), and
should be an atom name such as \fBSTRING\fR or \fBFILE_NAME\fR; see the
Inter-Client Communication Conventions Manual for complete details.
\fIType\fR defaults to \fBSTRING\fR.  The selection owner may choose to
return the selection in any of several different representation
formats, such as \fBSTRING\fR, \fBUTF8_STRING\fR, \fBATOM\fR,
\fBINTEGER\fR, etc. (this format is different
than the selection type; see the ICCCM for all the confusing details).
If the selection is returned in a non-string format, such as \fBINTEGER\fR
or \fBATOM\fR, the \fBselection\fR command converts it to string format as a
collection of fields separated by spaces: atoms are converted to their
textual names, and anything else is converted to hexadecimal integers.
Note that \fBselection get\fR does not retrieve the selection in the
\fBUTF8_STRING\fR format unless told to.
.\" METHOD: handle
.TP
\fBselection handle\fR ?\fB\-selection\fI s\fR? ?\fB\-type\fI t\fR? ?\fB\-format\fI f\fR? \fIwindow command\fR
.
Creates a handler for selection requests, such that \fIcommand\fR will
be executed whenever selection \fIs\fR is owned by \fIwindow\fR and
someone attempts to retrieve it in the form given by type \fIt\fR
(e.g. \fIt\fR is specified in the \fBselection get\fR command).
\fIS\fR defaults to \fBPRIMARY\fR, \fIt\fR defaults to \fBSTRING\fR, and
\fIf\fR defaults to \fBSTRING\fR.  If \fIcommand\fR is an empty string
then any existing handler for \fIwindow\fR, \fIt\fR, and
\fIs\fR is removed.
Note that when the selection is handled as type \fBSTRING\fR it is also
automatically handled as type \fBUTF8_STRING\fR as well.
.RS
.PP
When \fIselection\fR is requested, \fIwindow\fR is the selection owner,
and \fItype\fR is the requested type, \fIcommand\fR will be executed
as a Tcl command with two additional numbers appended to it
(with space separators).
The two additional numbers
are \fIoffset\fR and \fImaxChars\fR:  \fIoffset\fR specifies a starting
character position in the selection and \fImaxChars\fR gives the maximum
number of characters to retrieve.  The command should return a value consisting
of at most \fImaxChars\fR of the selection, starting at position
\fIoffset\fR.  For very large selections (larger than \fImaxChars\fR)
the selection will be retrieved using several invocations of \fIcommand\fR
with increasing \fIoffset\fR values.  If \fIcommand\fR returns a string
whose length is less than \fImaxChars\fR, the return value is assumed to
include all of the remainder of the selection;  if the length of
\fIcommand\fR's result is equal to \fImaxChars\fR then
\fIcommand\fR will be invoked again, until it eventually
returns a result shorter than \fImaxChars\fR.  The value of \fImaxChars\fR
will always be relatively large (thousands of characters).
.PP
If \fIcommand\fR returns an error then the selection retrieval is rejected
just as if the selection did not exist at all.
.PP
The \fIformat\fR argument specifies the representation that should be
used to transmit the selection to the requester (the second column of
Table 2 of the ICCCM), and defaults to \fBSTRING\fR.  If \fIformat\fR is
\fBSTRING\fR, the selection is transmitted as 8-bit ASCII characters (i.e.
just in the form returned by \fIcommand\fR, in the system \fBencoding\fR;
the \fBUTF8_STRING\fR format always uses UTF-8 as its encoding).
If \fIformat\fR is
\fBATOM\fR, then the return value from \fIcommand\fR is divided into fields
separated by white space;  each field is converted to its atom value,
and the 32-bit atom value is transmitted instead of the atom name.
For any other \fIformat\fR, the return value from \fIcommand\fR is
divided into fields separated by white space and each field is
converted to a 32-bit integer;  an array of integers is transmitted
to the selection requester.
.PP
The \fIformat\fR argument is needed only for compatibility with
selection requesters that do not use Tk.  If Tk is being
used to retrieve the selection then the value is converted back to
a string at the requesting end, so \fIformat\fR is
irrelevant.
.RE
.\" METHOD: own
.TP
\fBselection own\fR ?\fB\-displayof\fI window\fR? ?\fB\-selection\fI selection\fR?
.TP
\fBselection own\fR ?\fB\-command\fI command\fR? ?\fB\-selection\fI selection\fR? \fIwindow\fR
.
The first form of \fBselection own\fR returns the path name of the
window in this application that owns \fIselection\fR on the display
containing \fIwindow\fR, or an empty string if no window in this
application owns the selection.  \fISelection\fR defaults to \fBPRIMARY\fR and
\fIwindow\fR defaults to
.QW . .
.RS
.PP
The second form of \fBselection own\fR causes \fIwindow\fR to become
the new owner of \fIselection\fR on \fIwindow\fR's display, returning
an empty string as result. The existing owner, if any, is notified
that it has lost the selection.
If \fIcommand\fR is specified, it is a Tcl script to execute when
some other window claims ownership of the selection away from
\fIwindow\fR.  \fISelection\fR defaults to PRIMARY.
.RE
.SH WIDGET FACILITIES
.PP
The \fBtext\fR, \fBentry\fR, \fBttk::entry\fR, \fBlistbox\fR, \fBspinbox\fR
and \fBttk::spinbox\fR widgets have the option \fB\-exportselection\fR.  If a
widget has this option set to boolean \fBtrue\fR, then (in an unsafe
interpreter) a selection made in the widget is automatically written to the
\fBPRIMARY\fR selection.
.PP
A GUI event, for example \fB<<PasteSelection>>\fR, can copy the \fBPRIMARY\fR
selection to certain widgets.  This copy is implemented by a widget binding to
the event.  The binding script makes appropriate calls to the \fBselection\fR
command.
.PP
.SH PORTABILITY ISSUES
.PP
On X11, the \fBPRIMARY\fR selection is a system-wide feature of the X server,
allowing communication between different processes that are X11 clients.
.PP
On Windows, the \fBPRIMARY\fR selection is not provided by the system, but
only by Tk, and so it is shared only between windows of a parent interpreter
and its child interpreters.  It is not shared between interpreters in
different processes or different threads.  Each parent interpreter has a
separate \fBPRIMARY\fR selection that is shared only with its child
interpreters which are not safe interpreters.
.PP
.SH SECURITY
.PP
A safe interpreter cannot read from the \fBPRIMARY\fR selection because its
\fBselection\fR command is hidden.  For this reason the \fBPRIMARY\fR
selection cannot be written to the Tk widgets of a safe interpreter.
.PP
A Tk widget can have its option \fB\-exportselection\fR set to boolean
\fBtrue\fR, but in a safe interpreter this option has no effect: writing
from the widget to the \fBPRIMARY\fR selection is disabled.
.PP
These are security features.  A safe interpreter may run untrusted code, and
it is a security risk if this untrusted code can read or write the
\fBPRIMARY\fR selection used by other interpreters.
.PP
.SH EXAMPLES
.PP
On X11 platforms, one of the standard selections available is the
\fBSECONDARY\fR selection. Hardly anything uses it, but here is how to read
it using Tk:
.PP
.CS
set selContents [\fBselection get\fR -selection SECONDARY]
.CE
.PP
Many different types of data may be available for a selection; the
special type \fBTARGETS\fR allows you to get a list of available types:
.PP
.CS
foreach type [\fBselection get\fR -type TARGETS] {
   puts "Selection PRIMARY supports type $type"
}
.CE
.PP
To claim the selection, you must first set up a handler to supply the
data for the selection. Then you have to claim the selection...
.CS
# Set up the data handler ready for incoming requests
set foo "This is a string with some data in it... blah blah"
\fBselection handle\fR -selection SECONDARY . getData
proc getData {offset maxChars} {
   puts "Retrieving selection starting at $offset"
   return [string range $::foo $offset [expr {$offset+$maxChars-1}]]
}

# Now we grab the selection itself
puts "Claiming selection"
\fBselection own\fR -command lost -selection SECONDARY .
proc lost {} {
   puts "Lost selection"
}
.CE
.SH "SEE ALSO"
clipboard(n)
.SH KEYWORDS
clear, format, handler, ICCCM, own, selection, target, type
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