bind(n) Tk Built-In Commands bind(n)
NAME
bind - Arrange for X events to invoke Tcl scripts
SYNOPSIS
bind tag ?sequence? ?+??script?
INTRODUCTION
The bind command associates Tcl scripts with X events. If all three
arguments are specified, bind will arrange for script (a Tcl script) to
be evaluated whenever the event(s) given by sequence occur in the win-
dow(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
sequences 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:
o If a tag is the name of an internal window the binding applies to
that window.
o If the tag is the name of a toplevel window the binding applies to
the toplevel window and all its internal windows.
o If the tag is the name of a class of widgets, such as Button, the
binding applies to all widgets in that class;
o 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: <modi-
fier-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 sep-
arated 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 brackets. 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 vir-
tual event is defined, and if the definition of a virtual event changes
dynamically, all windows bound to that virtual event will respond imme-
diately to the new definition.
Some widgets (e.g. menu and text) issue virtual events when their
internal 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: Con-
trol Mod1, M1, Command Alt Mod2,
M2, Option Shift Mod3, M3
Lock Mod4, M4 Extended Mod5, M5 But-
ton1, 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
occur close together in time and without substantial mouse motion in
between. For example, <Double-Button-1> is equivalent to <But-
ton-1><Button-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 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
extra abbreviations. The type field will also accept a couple non-
standard 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. Acti-
vate Destroy Map ButtonPress, But-
ton Enter MapRequest ButtonRe-
lease Expose Motion Circu-
late FocusIn MouseWheel CirculateRequest Focu-
sOut Property Colormap Gravity Reparent
Configure KeyPress, KeyResizeRequest Configur-
eRequest KeyRelease Unmap Cre-
ate Leave Visibility Deactivate Most of the
above events have the same fields and behaviors as events in the X Win-
dowing system. You can find more detailed descriptions of these events
in any X window programming book. A couple of the events are exten-
sions 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. Like Key events the event is always
routed to the window that currently has focus. When the event is
received you can use the %D substitution to get the delta field
for the event, which is a integer value describing how the mouse
wheel has moved. The smallest value for which the system will
report is defined by the OS. On Windows 95 & 98 machines this
value is at least 120 before it is reported. However, higher res-
olution devices may be available in the future. The sign of the
value determines which direction your widget should scroll. Posi-
tive values should scroll up and negative values should scroll
down.
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
become mapped when they transition to the normal state, and are
unmapped 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 state:
the widget still exists, but most operations on it will fail.
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, focus events are sent to the intermediate 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 win-
dow 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 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
belonging 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
reliable way to track changes to a window's position in the stack-
ing 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
occurs. 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. is the keysym for the ASCII character plus
descriptions for non-alphanumeric characters plus descriptions for all
the non-ASCII keys on the keyboard (e.g. is the keysym for the left
shift key, and 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, which will be executed
whenever the given event sequence occurs. 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
immediately 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 NotifyDetail-
None NotifyPointer NotifyInferior NotifyPointer-
Root NotifyNonlinear NotifyVirtual For ConfigureRequest
events, the string will be one of: Above Oppo-
site 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
integer. 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
receiving window. 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). XmbLookupString (or
XLookupString when input method support is turned off) does all
the work of translating from the event to a UNICODE character.
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. On Windows 95 & 98 systems the smallest value for the
delta is 120. Future systems may support higher resolution values
for the delta. 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 event, 1 indicates that it is a event
generated by SendEvent.
%K The keysym corresponding to the event, substituted as a textual
string. Valid only for KeyPress and KeyRelease events.
%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, KeyPress, KeyRelease,
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 it will be surrounded with braces if it
contains 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 evaluated. Most replacements
are numbers or well-defined strings such as Above; for these replace-
ments no special formatting is ever necessary. The most common case
where reformatting occurs is for the %A substitution. For example, if
script is insert %A and the character typed is an open square bracket,
then the script actually 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,
then the current binding script is terminated but Tk will continue pro-
cessing binding scripts associated with other tag's. If the break com-
mand is invoked within a binding script, then that script terminates
and no other scripts will be invoked for the event.
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
sequence 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 unde-
fined.
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
sequence. 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
ignored 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
Motion 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(n), bindtags(n), event(n), focus(n), grab(n), keysyms(n)
KEYWORDS
binding, event
Tk 8.0 bind(n)
bind 8.5.4 - Generated Fri Aug 22 18:07:11 CDT 2008