Provided by: tk8.6-doc_8.6.14-1build1_all 
NAME
selection - Manipulate the X selection
SYNOPSIS
selection option ?arg arg ...?
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DESCRIPTION
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).
Note that for management of the CLIPBOARD selection (see below), the clipboard command may also be used.
The first argument to selection determines the format of the rest of the arguments and the behavior of
the command. The following forms are currently supported:
selection clear ?-displayof window? ?-selection selection?
If selection exists anywhere on window's display, clear it so that no window owns the selection
anymore. Selection specifies the X selection that should be cleared, and should be an atom name
such as PRIMARY or CLIPBOARD; see the Inter-Client Communication Conventions Manual for complete
details. Selection defaults to PRIMARY and window defaults to “.”. Returns an empty string.
selection get ?-displayof window? ?-selection selection? ?-type type?
Retrieves the value of selection from window's display and returns it as a result. Selection
defaults to PRIMARY and window defaults to “.”. Type specifies the form in which the selection is
to be returned (the desired “target” for conversion, in ICCCM terminology), and should be an atom
name such as STRING or FILE_NAME; see the Inter-Client Communication Conventions Manual for
complete details. Type defaults to STRING. The selection owner may choose to return the
selection in any of several different representation formats, such as STRING, UTF8_STRING, ATOM,
INTEGER, 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 INTEGER or ATOM,
the selection 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 selection get does not retrieve the selection in the UTF8_STRING format
unless told to.
selection handle ?-selection s? ?-type t? ?-format f? window command
Creates a handler for selection requests, such that command will be executed whenever selection s
is owned by window and someone attempts to retrieve it in the form given by type t (e.g. t is
specified in the selection get command). S defaults to PRIMARY, t defaults to STRING, and f
defaults to STRING. If command is an empty string then any existing handler for window, t, and s
is removed. Note that when the selection is handled as type STRING it is also automatically
handled as type UTF8_STRING as well.
When selection is requested, window is the selection owner, and type is the requested type,
command will be executed as a Tcl command with two additional numbers appended to it (with space
separators). The two additional numbers are offset and maxChars: offset specifies a starting
character position in the selection and maxChars gives the maximum number of characters to
retrieve. The command should return a value consisting of at most maxChars of the selection,
starting at position offset. For very large selections (larger than maxChars) the selection will
be retrieved using several invocations of command with increasing offset values. If command
returns a string whose length is less than maxChars, the return value is assumed to include all of
the remainder of the selection; if the length of command's result is equal to maxChars then
command will be invoked again, until it eventually returns a result shorter than maxChars. The
value of maxChars will always be relatively large (thousands of characters).
If command returns an error then the selection retrieval is rejected just as if the selection did
not exist at all.
The format 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 STRING. If format is
STRING, the selection is transmitted as 8-bit ASCII characters (i.e. just in the form returned by
command, in the system encoding; the UTF8_STRING format always uses UTF-8 as its encoding). If
format is ATOM, then the return value from command 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 format, the return value from command 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.
The format 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 format is irrelevant.
selection own ?-displayof window? ?-selection selection?
selection own ?-command command? ?-selection selection? window
The first form of selection own returns the path name of the window in this application that owns
selection on the display containing window, or an empty string if no window in this application
owns the selection. Selection defaults to PRIMARY and window defaults to “.”.
The second form of selection own causes window to become the new owner of selection on window's
display, returning an empty string as result. The existing owner, if any, is notified that it has
lost the selection. If command is specified, it is a Tcl script to execute when some other window
claims ownership of the selection away from window. Selection defaults to PRIMARY.
WIDGET FACILITIES
The text, entry, ttk::entry, listbox, spinbox and ttk::spinbox widgets have the option -exportselection.
If a widget has this option set to boolean true, then (in an unsafe interpreter) a selection made in the
widget is automatically written to the PRIMARY selection.
A GUI event, for example <<PasteSelection>>, can copy the PRIMARY selection to certain widgets. This
copy is implemented by a widget binding to the event. The binding script makes appropriate calls to the
selection command.
PORTABILITY ISSUES
On X11, the PRIMARY selection is a system-wide feature of the X server, allowing communication between
different processes that are X11 clients.
On Windows, the PRIMARY 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 PRIMARY
selection that is shared only with its child interpreters which are not safe interpreters.
SECURITY
A safe interpreter cannot read from the PRIMARY selection because its selection command is hidden. For
this reason the PRIMARY selection cannot be written to the Tk widgets of a safe interpreter.
A Tk widget can have its option -exportselection set to boolean true, but in a safe interpreter this
option has no effect: writing from the widget to the PRIMARY selection is disabled.
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 PRIMARY selection used by other interpreters.
EXAMPLES
On X11 platforms, one of the standard selections available is the SECONDARY selection. Hardly anything
uses it, but here is how to read it using Tk:
set selContents [selection get -selection SECONDARY]
Many different types of data may be available for a selection; the special type TARGETS allows you to get
a list of available types:
foreach type [selection get -type TARGETS] {
puts "Selection PRIMARY supports type $type"
}
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...
# Set up the data handler ready for incoming requests
set foo "This is a string with some data in it... blah blah"
selection handle -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"
selection own -command lost -selection SECONDARY .
proc lost {} {
puts "Lost selection"
}
SEE ALSO
clipboard(3tk)
KEYWORDS
clear, format, handler, ICCCM, own, selection, target, type
Tk 8.1 selection(3tk)