bind(3tk) Tk Built-In Commands bind(3tk)
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NAME
bind - Arrange for X events to invoke Tcl scripts
SYNOPSIS
bind tag ?sequence? ?+??script?
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INTRODUCTION
The bind command associates Tcl scripts with X events. If all three
arguments are specified, bind will arrange for script (a Tcl script
called the “binding script”) to be evaluated whenever the event(s)
given by sequence occur in the window(s) identified by tag. If script
is prefixed with a “+”, then it is appended to any existing binding for
sequence; otherwise script replaces any existing binding. If script
is an empty string then the current binding for sequence is destroyed,
leaving sequence unbound. In all of the cases where a script argument
is provided, bind returns an empty string.
If sequence is specified without a script, then the script currently
bound to sequence is returned, or an empty string is returned if there
is no binding for sequence. If neither sequence nor script is speci-
fied, then the return value is a list whose elements are all the se-
quences for which there exist bindings for tag.
The tag argument determines which window(s) the binding applies to. If
tag begins with a dot, as in .a.b.c, then it must be the path name for
a window; otherwise it may be an arbitrary string. Each window has an
associated list of tags, and a binding applies to a particular window
if its tag is among those specified for the window. Although the bind-
tags command may be used to assign an arbitrary set of binding tags to
a window, the default binding tags provide the following behavior:
• If a tag is the name of an internal window the binding applies to
that window.
• If the tag is the name of a toplevel window the binding applies to
the toplevel window and all its internal windows.
• If the tag is the name of a class of widgets, such as Button, the
binding applies to all widgets in that class;
• If tag has the value all, the binding applies to all windows in the
application.
EVENT PATTERNS
The sequence argument specifies a sequence of one or more event pat-
terns, with optional white space between the patterns. Each event pat-
tern may take one of three forms. In the simplest case it is a single
printing ASCII character, such as a or [. The character may not be a
space character or the character <. This form of pattern matches a
KeyPress event for the particular character. The second form of pat-
tern is longer but more general. It has the following syntax:
<modifier-modifier-type-detail>
The entire event pattern is surrounded by angle brackets. Inside the
angle brackets are zero or more modifiers, an event type, and an extra
piece of information (detail) identifying a particular button or
keysym. Any of the fields may be omitted, as long as at least one of
type and detail is present. The fields must be separated by white
space or dashes.
The third form of pattern is used to specify a user-defined, named vir-
tual event. It has the following syntax:
<<name>>
The entire virtual event pattern is surrounded by double angle brack-
ets. Inside the angle brackets is the user-defined name of the virtual
event. Modifiers, such as Shift or Control, may not be combined with a
virtual event to modify it. Bindings on a virtual event may be created
before the virtual event is defined, and if the definition of a virtual
event changes dynamically, all windows bound to that virtual event will
respond immediately to the new definition.
Some widgets (e.g. menu and text) issue virtual events when their in-
ternal state is updated in some ways. Please see the manual page for
each widget for details.
MODIFIERS
Modifiers consist of any of the following values:
Control Mod1, M1, Command
Alt Mod2, M2, Option
Shift Mod3, M3
Lock Mod4, M4
Extended Mod5, M5
Button1, B1 Meta, M
Button2, B2 Double
Button3, B3 Triple
Button4, B4 Quadruple
Button5, B5
Where more than one value is listed, separated by commas, the values
are equivalent. Most of the modifiers have the obvious X meanings.
For example, Button1 requires that button 1 be depressed when the event
occurs. For a binding to match a given event, the modifiers in the
event must include all of those specified in the event pattern. An
event may also contain additional modifiers not specified in the bind-
ing. For example, if button 1 is pressed while the shift and control
keys are down, the pattern <Control-Button-1> will match the event, but
<Mod1-Button-1> will not. If no modifiers are specified, then any com-
bination of modifiers may be present in the event.
Meta and M refer to whichever of the M1 through M5 modifiers is associ-
ated with the Meta key(s) on the keyboard (keysyms Meta_R and Meta_L).
If there are no Meta keys, or if they are not associated with any modi-
fiers, then Meta and M will not match any events. Similarly, the Alt
modifier refers to whichever modifier is associated with the alt key(s)
on the keyboard (keysyms Alt_L and Alt_R).
The Double, Triple and Quadruple modifiers are a convenience for speci-
fying double mouse clicks and other repeated events. They cause a par-
ticular event pattern to be repeated 2, 3 or 4 times, and also place a
time and space requirement on the sequence: for a sequence of events to
match a Double, Triple or Quadruple pattern, all of the events must oc-
cur close together in time and without substantial mouse motion in be-
tween. For example, <Double-Button-1> is equivalent to <Button-1><But-
ton-1> with the extra time and space requirement.
The Command and Option modifiers are equivalents of Mod1 resp. Mod2,
they correspond to Macintosh-specific modifier keys.
The Extended modifier is, at present, specific to Windows. It appears
on events that are associated with the keys on the “extended keyboard”.
On a US keyboard, the extended keys include the Alt and Control keys at
the right of the keyboard, the cursor keys in the cluster to the left
of the numeric pad, the NumLock key, the Break key, the PrintScreen
key, and the / and Enter keys in the numeric keypad.
EVENT TYPES
The type field may be any of the standard X event types, with a few ex-
tra abbreviations. The type field will also accept a couple non-stan-
dard X event types that were added to better support the Macintosh and
Windows platforms. Below is a list of all the valid types; where two
names appear together, they are synonyms.
Activate Destroy Map
ButtonPress, Button Enter MapRequest
ButtonRelease Expose Motion
Circulate FocusIn MouseWheel
CirculateRequest FocusOut Property
Colormap Gravity Reparent
Configure KeyPress, Key ResizeRequest
ConfigureRequest KeyRelease Unmap
Create Leave Visibility
Deactivate
Most of the above events have the same fields and behaviors as events
in the X Windowing system. You can find more detailed descriptions of
these events in any X window programming book. A couple of the events
are extensions to the X event system to support features unique to the
Macintosh and Windows platforms. We provide a little more detail on
these events here. These include:
Activate, Deactivate
These two events are sent to every sub-window of a toplevel when
they change state. In addition to the focus Window, the Macintosh
platform and Windows platforms have a notion of an active window
(which often has but is not required to have the focus). On the
Macintosh, widgets in the active window have a different appear-
ance than widgets in deactive windows. The Activate event is sent
to all the sub-windows in a toplevel when it changes from being
deactive to active. Likewise, the Deactive event is sent when the
window's state changes from active to deactive. There are no use-
ful percent substitutions you would make when binding to these
events.
MouseWheel
Many contemporary mice support a mouse wheel, which is used for
scrolling documents without using the scrollbars. By rolling the
wheel, the system will generate MouseWheel events that the appli-
cation can use to scroll. The event is routed to the window cur-
rently under the mouse pointer. When the event is received you can
use the %D substitution to get the delta field for the event,
which is an integer value describing how the mouse wheel has
moved. The smallest value for which the system will report is de-
fined by the OS. The sign of the value determines which direction
your widget should scroll. Positive values should scroll up and
negative values should scroll down.
Horizontal scrolling uses Shift-MouseWheel events, with positive
%D delta substitution indicating left scrolling and negative right
scrolling. Only Windows and macOS Aqua typically fire MouseWheel
and Shift-MouseWheel events. On X11 vertical scrolling is rather
supported through Button-4 and Button-5 events, and horizontal
scrolling through Shift-Button-4 and Shift-Button-5 events. Hori-
zontal scrolling events may fire from many different hardware
units such as tilt wheels or touchpads. Horizontal scrolling can
also be emulated by holding Shift and scrolling vertically.
KeyPress, KeyRelease
The KeyPress and KeyRelease events are generated whenever a key is
pressed or released. KeyPress and KeyRelease events are sent to
the window which currently has the keyboard focus.
ButtonPress, ButtonRelease, Motion
The ButtonPress and ButtonRelease events are generated when the
user presses or releases a mouse button. Motion events are gener-
ated whenever the pointer is moved. ButtonPress, ButtonRelease,
and Motion events are normally sent to the window containing the
pointer.
When a mouse button is pressed, the window containing the pointer
automatically obtains a temporary pointer grab. Subsequent But-
tonPress, ButtonRelease, and Motion events will be sent to that
window, regardless of which window contains the pointer, until all
buttons have been released.
Configure
A Configure event is sent to a window whenever its size, position,
or border width changes, and sometimes when it has changed posi-
tion in the stacking order.
Map, Unmap
The Map and Unmap events are generated whenever the mapping state
of a window changes.
Windows are created in the unmapped state. Top-level windows be-
come mapped when they transition to the normal state, and are un-
mapped in the withdrawn and iconic states. Other windows become
mapped when they are placed under control of a geometry manager
(for example pack or grid).
A window is viewable only if it and all of its ancestors are
mapped. Note that geometry managers typically do not map their
children until they have been mapped themselves, and unmap all
children when they become unmapped; hence in Tk Map and Unmap
events indicate whether or not a window is viewable.
Visibility
A window is said to be obscured when another window above it in
the stacking order fully or partially overlaps it. Visibility
events are generated whenever a window's obscurity state changes;
the state field (%s) specifies the new state.
Expose
An Expose event is generated whenever all or part of a window
should be redrawn (for example, when a window is first mapped or
if it becomes unobscured). It is normally not necessary for
client applications to handle Expose events, since Tk handles them
internally.
Destroy
A Destroy event is delivered to a window when it is destroyed.
When the Destroy event is delivered to a widget, it is in a “half-
dead” state: the widget still exists, but operations that involve
it may return invalid results, or return an error.
FocusIn, FocusOut
The FocusIn and FocusOut events are generated whenever the key-
board focus changes. A FocusOut event is sent to the old focus
window, and a FocusIn event is sent to the new one.
In addition, if the old and new focus windows do not share a com-
mon parent, “virtual crossing” focus events are sent to the inter-
mediate windows in the hierarchy. Thus a FocusIn event indicates
that the target window or one of its descendants has acquired the
focus, and a FocusOut event indicates that the focus has been
changed to a window outside the target window's hierarchy.
The keyboard focus may be changed explicitly by a call to focus,
or implicitly by the window manager.
Enter, Leave
An Enter event is sent to a window when the pointer enters that
window, and a Leave event is sent when the pointer leaves it.
If there is a pointer grab in effect, Enter and Leave events are
only delivered to the window owning the grab.
In addition, when the pointer moves between two windows, Enter and
Leave “virtual crossing” events are sent to intermediate windows
in the hierarchy in the same manner as for FocusIn and FocusOut
events.
Property
A Property event is sent to a window whenever an X property be-
longing to that window is changed or deleted. Property events are
not normally delivered to Tk applications as they are handled by
the Tk core.
Colormap
A Colormap event is generated whenever the colormap associated
with a window has been changed, installed, or uninstalled.
Widgets may be assigned a private colormap by specifying a -col-
ormap option; the window manager is responsible for installing and
uninstalling colormaps as necessary.
Note that Tk provides no useful details for this event type.
MapRequest, CirculateRequest, ResizeRequest, ConfigureRequest, Create
These events are not normally delivered to Tk applications. They
are included for completeness, to make it possible to write X11
window managers in Tk. (These events are only delivered when a
client has selected SubstructureRedirectMask on a window; the Tk
core does not use this mask.)
Gravity, Reparent, Circulate
The events Gravity and Reparent are not normally delivered to Tk
applications. They are included for completeness.
A Circulate event indicates that the window has moved to the top
or to the bottom of the stacking order as a result of an XCircu-
lateSubwindows protocol request. Note that the stacking order may
be changed for other reasons which do not generate a Circulate
event, and that Tk does not use XCirculateSubwindows() internally.
This event type is included only for completeness; there is no re-
liable way to track changes to a window's position in the stacking
order.
EVENT DETAILS
The last part of a long event specification is detail. In the case of
a ButtonPress or ButtonRelease event, it is the number of a button
(1-5). If a button number is given, then only an event on that partic-
ular button will match; if no button number is given, then an event on
any button will match. Note: giving a specific button number is dif-
ferent than specifying a button modifier; in the first case, it refers
to a button being pressed or released, while in the second it refers to
some other button that is already depressed when the matching event oc-
curs. If a button number is given then type may be omitted: if will
default to ButtonPress. For example, the specifier <1> is equivalent
to <ButtonPress-1>.
If the event type is KeyPress or KeyRelease, then detail may be speci-
fied in the form of an X keysym. Keysyms are textual specifications
for particular keys on the keyboard; they include all the alphanumeric
ASCII characters (e.g. “a” is the keysym for the ASCII character “a”),
plus descriptions for non-alphanumeric characters (“comma”is the keysym
for the comma character), plus descriptions for all the non-ASCII keys
on the keyboard (e.g. “Shift_L” is the keysym for the left shift key,
and “F1” is the keysym for the F1 function key, if it exists). The
complete list of keysyms is not presented here; it is available in
other X documentation and may vary from system to system. If neces-
sary, you can use the %K notation described below to print out the
keysym name for a particular key. If a keysym detail is given, then
the type field may be omitted; it will default to KeyPress. For exam-
ple, <Control-comma> is equivalent to <Control-KeyPress-comma>.
BINDING SCRIPTS AND SUBSTITUTIONS
The script argument to bind is a Tcl script, called the “binding
script”, which will be executed whenever the given event sequence oc-
curs. Command will be executed in the same interpreter that the bind
command was executed in, and it will run at global level (only global
variables will be accessible). If script contains any % characters,
then the script will not be executed directly. Instead, a new script
will be generated by replacing each %, and the character following it,
with information from the current event. The replacement depends on
the character following the %, as defined in the list below. Unless
otherwise indicated, the replacement string is the decimal value of the
given field from the current event. Some of the substitutions are only
valid for certain types of events; if they are used for other types of
events the value substituted is undefined.
%% Replaced with a single percent.
%# The number of the last client request processed by the server (the
serial field from the event). Valid for all event types.
%a The above field from the event, formatted as a hexadecimal number.
Valid only for Configure events. Indicates the sibling window im-
mediately below the receiving window in the stacking order, or 0
if the receiving window is at the bottom.
%b The number of the button that was pressed or released. Valid only
for ButtonPress and ButtonRelease events.
%c The count field from the event. Valid only for Expose events.
Indicates that there are count pending Expose events which have
not yet been delivered to the window.
%d The detail or user_data field from the event. The %d is replaced
by a string identifying the detail. For Enter, Leave, FocusIn,
and FocusOut events, the string will be one of the following:
NotifyAncestor NotifyNonlinearVirtual
NotifyDetailNone NotifyPointer
NotifyInferior NotifyPointerRoot
NotifyNonlinear NotifyVirtual
For ConfigureRequest events, the string will be one of:
Above Opposite
Below None
BottomIf TopIf
For virtual events, the string will be whatever value is stored in
the user_data field when the event was created (typically with
event generate), or the empty string if the field is NULL. Vir-
tual events corresponding to key sequence presses (see event add
for details) set the user_data to NULL. For events other than
these, the substituted string is undefined.
%f The focus field from the event (0 or 1). Valid only for Enter and
Leave events. 1 if the receiving window is the focus window or a
descendant of the focus window, 0 otherwise.
%h The height field from the event. Valid for the Configure, Config-
ureRequest, Create, ResizeRequest, and Expose events. Indicates
the new or requested height of the window.
%i The window field from the event, represented as a hexadecimal in-
teger. Valid for all event types.
%k The keycode field from the event. Valid only for KeyPress and
KeyRelease events.
%m The mode field from the event. The substituted string is one of
NotifyNormal, NotifyGrab, NotifyUngrab, or NotifyWhileGrabbed.
Valid only for Enter, FocusIn, FocusOut, and Leave events.
%o The override_redirect field from the event. Valid only for Map,
Reparent, and Configure events.
%p The place field from the event, substituted as one of the strings
PlaceOnTop or PlaceOnBottom. Valid only for Circulate and Circu-
lateRequest events.
%s The state field from the event. For ButtonPress, ButtonRelease,
Enter, KeyPress, KeyRelease, Leave, and Motion events, a decimal
string is substituted. For Visibility, one of the strings Visi-
bilityUnobscured, VisibilityPartiallyObscured, and VisibilityFul-
lyObscured is substituted. For Property events, substituted with
either the string NewValue (indicating that the property has been
created or modified) or Delete (indicating that the property has
been removed).
%t The time field from the event. This is the X server timestamp
(typically the time since the last server reset) in milliseconds,
when the event occurred. Valid for most events.
%w The width field from the event. Indicates the new or requested
width of the window. Valid only for Configure, ConfigureRequest,
Create, ResizeRequest, and Expose events.
%x, %y
The x and y fields from the event. For ButtonPress, ButtonRe-
lease, Motion, KeyPress, KeyRelease, and MouseWheel events, %x and
%y indicate the position of the mouse pointer relative to the re-
ceiving window. For key events on the Macintosh these are the co-
ordinates of the mouse at the moment when an X11 KeyEvent is sent
to Tk, which could be slightly later than the time of the physical
press or release. For Enter and Leave events, the position where
the mouse pointer crossed the window, relative to the receiving
window. For Configure and Create requests, the x and y coordi-
nates of the window relative to its parent window.
%A Substitutes the UNICODE character corresponding to the event, or
the empty string if the event does not correspond to a UNICODE
character (e.g. the shift key was pressed). On X11, XmbLookup-
String (or XLookupString when input method support is turned off)
does all the work of translating from the event to a UNICODE char-
acter. On X11, valid only for KeyPress event. On Windows and
macOS/aqua, valid only for KeyPress and KeyRelease events.
%B The border_width field from the event. Valid only for Configure,
ConfigureRequest, and Create events.
%D This reports the delta value of a MouseWheel event. The delta
value represents the rotation units the mouse wheel has been
moved. The sign of the value represents the direction the mouse
wheel was scrolled.
%E The send_event field from the event. Valid for all event types.
0 indicates that this is a “normal” event, 1 indicates that it is
a “synthetic” event generated by SendEvent.
%K The keysym corresponding to the event, substituted as a textual
string. Valid only for KeyPress and KeyRelease events.
%M The number of script-based binding patterns matched so far for the
event. Valid for all event types.
%N The keysym corresponding to the event, substituted as a decimal
number. Valid only for KeyPress and KeyRelease events.
%P The name of the property being updated or deleted (which may be
converted to an XAtom using winfo atom.) Valid only for Property
events.
%R The root window identifier from the event. Valid only for events
containing a root field.
%S The subwindow window identifier from the event, formatted as a
hexadecimal number. Valid only for events containing a subwindow
field.
%T The type field from the event. Valid for all event types.
%W The path name of the window to which the event was reported (the
window field from the event). Valid for all event types.
%X, %Y
The x_root and y_root fields from the event. If a virtual-root
window manager is being used then the substituted values are the
corresponding x-coordinate and y-coordinate in the virtual root.
Valid only for ButtonPress, ButtonRelease, Enter, KeyPress, KeyRe-
lease, Leave and Motion events. Same meaning as %x and %y, except
relative to the (virtual) root window.
The replacement string for a %-replacement is formatted as a proper Tcl
list element. This means that spaces or special characters such as $
and { may be preceded by backslashes. This guarantees that the string
will be passed through the Tcl parser when the binding script is evalu-
ated. Most replacements are numbers or well-defined strings such as
Above; for these replacements no special formatting is ever necessary.
The most common case where reformatting occurs is for the %A substitu-
tion. For example, if script is
insert %A
and the character typed is an open square bracket, then the script ac-
tually executed will be
insert \[
This will cause the insert to receive the original replacement string
(open square bracket) as its first argument. If the extra backslash
had not been added, Tcl would not have been able to parse the script
correctly.
MULTIPLE MATCHES
It is possible for several bindings to match a given X event. If the
bindings are associated with different tag's, then each of the bindings
will be executed, in order. By default, a binding for the widget will
be executed first, followed by a class binding, a binding for its
toplevel, and an all binding. The bindtags command may be used to
change this order for a particular window or to associate additional
binding tags with the window.
The continue and break commands may be used inside a binding script to
control the processing of matching scripts. If continue is invoked
within a binding script, then this binding script, including all other
“+” appended scripts, is terminated but Tk will continue processing
binding scripts associated with other tag's. If the break command is
invoked within a binding script, then that script terminates and no
other scripts will be invoked for the event.
Within a script called from the binding script, return -code ok may be
used to continue processing (including “+” appended scripts), or return
-code break may be used to stop processing all other binding scripts.
If more than one binding matches a particular event and they have the
same tag, then the most specific binding is chosen and its script is
evaluated. The following tests are applied, in order, to determine
which of several matching sequences is more specific:
(a) an event pattern that specifies a specific button or key
is more specific than one that does not;
(b) a longer sequence (in terms of number of events matched)
is more specific than a shorter sequence;
(c) if the modifiers specified in one pattern are a subset of
the modifiers in another pattern, then the pattern with
more modifiers is more specific;
(d) a virtual event whose physical pattern matches the se-
quence is less specific than the same physical pattern
that is not associated with a virtual event;
(e) given a sequence that matches two or more virtual events,
one of the virtual events will be chosen, but the order
is undefined.
If the matching sequences contain more than one event, then tests
(c)-(e) are applied in order from the most recent event to the least
recent event in the sequences. If these tests fail to determine a win-
ner, then the most recently registered sequence is the winner.
If there are two (or more) virtual events that are both triggered by
the same sequence, and both of those virtual events are bound to the
same window tag, then only one of the virtual events will be triggered,
and it will be picked at random:
event add <<Paste>> <Control-y>
event add <<Paste>> <Button-2>
event add <<Scroll>> <Button-2>
bind Entry <<Paste>> {puts Paste}
bind Entry <<Scroll>> {puts Scroll}
If the user types Control-y, the <<Paste>> binding will be invoked, but
if the user presses button 2 then one of either the <<Paste>> or the
<<Scroll>> bindings will be invoked, but exactly which one gets invoked
is undefined.
If an X event does not match any of the existing bindings, then the
event is ignored. An unbound event is not considered to be an error.
MULTI-EVENT SEQUENCES AND IGNORED EVENTS
When a sequence specified in a bind command contains more than one
event pattern, then its script is executed whenever the recent events
(leading up to and including the current event) match the given se-
quence. This means, for example, that if button 1 is clicked repeat-
edly the sequence <Double-ButtonPress-1> will match each button press
but the first. If extraneous events that would prevent a match occur
in the middle of an event sequence then the extraneous events are ig-
nored unless they are KeyPress or ButtonPress events. For example,
<Double-ButtonPress-1> will match a sequence of presses of button 1,
even though there will be ButtonRelease events (and possibly Motion
events) between the ButtonPress events. Furthermore, a KeyPress event
may be preceded by any number of other KeyPress events for modifier
keys without the modifier keys preventing a match. For example, the
event sequence aB will match a press of the a key, a release of the a
key, a press of the Shift key, and a press of the b key: the press of
Shift is ignored because it is a modifier key. Finally, if several Mo-
tion events occur in a row, only the last one is used for purposes of
matching binding sequences.
ERRORS
If an error occurs in executing the script for a binding then the bger-
ror mechanism is used to report the error. The bgerror command will be
executed at global level (outside the context of any Tcl procedure).
EXAMPLES
Arrange for a string describing the motion of the mouse to be printed
out when the mouse is double-clicked:
bind . <Double-1> {
puts "hi from (%x,%y)"
}
A little GUI that displays what the keysym name of the last key pressed
is:
set keysym "Press any key"
pack [label .l -textvariable keysym -padx 2m -pady 1m]
bind . <Key> {
set keysym "You pressed %K"
}
SEE ALSO
bgerror(3tcl), bindtags(3tk), event(3tk), focus(3tk), grab(3tk),
keysyms(3tk)
KEYWORDS
binding, event
Tk 8.0 bind(3tk)
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