Provided by: tk8.6-doc_8.6.13-2_all 
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 specified, 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
bindtags 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 class of widgets, such as Button, the binding applies to
all widgets in that class.
• If the tag is the name of a toplevel window the binding applies to the toplevel window
and all its internal windows.
• 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 patterns, with optional
white space between the patterns. Each event pattern 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 pattern 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 virtual 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 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 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:
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 binding. 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
combination of modifiers may be present in the event.
Meta and M refer to whichever of the M1 through M5 modifiers is associated 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 modifiers, 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 specifying double mouse
clicks and other repeated events. They cause a particular 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 <Button-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 “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 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.
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 appearance 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 useful
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 application can use to scroll. The event is routed to the
window currently 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 defined 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. Horizontal
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 generated 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 ButtonPress, 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 position 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 “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 keyboard 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 common parent, “virtual
crossing” 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 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 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 -colormap 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 XCirculateSubwindows 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 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 particular button will match; if no button number is given,
then an event on any button will match. Note: giving a specific button number is
different 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 specified 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 necessary, 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 example, <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 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
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. Virtual 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, ConfigureRequest, 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 CirculateRequest 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 VisibilityUnobscured, VisibilityPartiallyObscured, and
VisibilityFullyObscured 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, ButtonRelease, Motion, KeyPress,
KeyRelease, and MouseWheel events, %x and %y indicate the position of the mouse
pointer relative to the receiving window. For key events on the Macintosh these are
the coordinates 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 coordinates
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, XmbLookupString (or XLookupString when input method support is
turned off) does all the work of translating from the event to a UNICODE character.
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, KeyRelease, 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 evaluated. 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 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 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 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 winner, 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 sequence. This means, for example, that if button 1 is clicked
repeatedly 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 bgerror 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