selection — Manipulate the X selection
selection clear ?-displayof window? ?-selection selection?
selection get ?-displayof window? ?-selection selection? ?-type type?
selection handle ?-selection s? ?-type t? ?-format f? window command
selection own ?-displayof window? ?-selection selection?
selection own ?-command command? ?-selection selection? window


selection — Manipulate the X selection


selection option ?arg arg ...?


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.


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


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