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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:



  

  
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.

  

  
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.

  

  
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.





  

  

  

  
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







  

    8.1
    Tk