selection(3tk) Tk Built-In Commands selection(3tk)
______________________________________________________________________________
NAME
selection - Manipulate the X selection
SYNOPSIS
selection option ?arg arg ...?
______________________________________________________________________________
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 Communi-
cation Conventions Manual for complete details. Selection de-
faults 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 re-
turns 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 dif-
ferent 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 se-
lection 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 hexadeci-
mal integers. Note that selection get does not retrieve the se-
lection 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 max-
Chars: 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 in-
creasing offset values. If command returns a string whose
length is less than maxChars, the return value is assumed to in-
clude all of the remainder of the selection; if the length of
command's result is equal to maxChars then command will be in-
voked 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 re-
jected 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 col-
umn of Table 2 of the ICCCM), and defaults to STRING. If format
is STRING, the selection is transmitted as 8-bit ASCII charac-
ters (i.e. just in the form returned by command, in the system
encoding; the UTF8_STRING format always uses UTF-8 as its encod-
ing). 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 trans-
mitted instead of the atom name. For any other format, the re-
turn 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 selec-
tion requesters that do not use Tk. If Tk is being used to re-
trieve 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 ap-
plication 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 se-
lection to certain widgets. This copy is implemented by a widget bind-
ing 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 inter-
preter and its child interpreters. It is not shared between inter-
preters in different processes or different threads. Each parent in-
terpreter 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 SEC-
ONDARY 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 spe-
cial 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)
Generated by dwww version 1.14 on Fri Jan 24 06:28:30 CET 2025.