### 3.2 bind

bind \- Arrange for X events to invoke Tcl commands

#### Synopsis

bind windowSpec
bind windowSpec sequence
bind windowSpec sequence command
bind windowSpec sequence +command

#### Description

If all three arguments are specified, bind will arrange for command (a Tcl command) to be executed whenever the sequence of events given by sequence occurs in the window(s) identified by windowSpec. If command is prefixed with a “+”, then it is appended to any existing binding for sequence; otherwise command replaces the existing binding, if any. If command is an empty string then the current binding for sequence is destroyed, leaving sequence unbound. In all of the cases where a command argument is provided, bind returns an empty string.

If sequence is specified without a command, then the command currently bound to sequence is returned, or an empty string if there is no binding for sequence. If neither sequence nor command is specified, then the return value is a list whose elements are all the sequences for which there exist bindings for windowSpec.

The windowSpec argument selects which window(s) the binding applies to. It may have one of three forms. If windowSpec is the path name for a window, then the binding applies to that particular window. If windowSpec is the name of a class of widgets, then the binding applies to all widgets in that class. Lastly, windowSpec may have the value all, in which case the binding applies to all windows in the application.

The sequence argument specifies a sequence of one or more event patterns, with optional white space between the patterns. Each event pattern may take either of two 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.

Modifiers may consist of any of the values in the following list:

    Control                  Any
    Shift                    Double
    Lock                     Triple
    Button1, B1              Mod1, M1, Meta, M
    Button2, B2              Mod2, M2, Alt
    Button3, B3              Mod3, M3
    Button4, B4              Mod4, M4
    Button5, B5              Mod5, M5

Where more than one value is listed, separated by commas, the values are equivalent. All of the modifiers except Any, Double, and Triple have the obvious X meanings. For example, Button1 requires that button 1 be depressed when the event occurs. Under normal conditions the button and modifier state at the time of the event must match exactly those specified in the bind command. If no modifiers are specified, then events will match only if no modifiers are present. If the Any modifier is specified, then additional modifiers may be present besides those specified explicitly. For example, if button 1 is pressed while the shift and control keys are down, the specifier <Any-Control-Button-1> will match the event, but the specifier <Control-Button-1> will not.

The Double and Triple modifiers are a convenience for specifying double mouse clicks and other repeated events. They cause a particular event pattern to be repeated 2 or 3 times, and also place a time and space requirement on the sequence: for a sequence of events to match a Double or Triple 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 type field may be any of the standard X event types, with a few extra abbreviations. Below is a list of all the valid types; where two name appear together, they are synonyms.

    ButtonPress, Button      Expose             Leave
    ButtonRelease            FocusIn            Map
    Circulate                FocusOut           Property
    CirculateRequest         Gravity            Reparent
    Colormap                 Keymap             ResizeRequest
    Configure                KeyPress, Key      Unmap
    ConfigureRequest         KeyRelease         Visibility
    Destroy                  MapRequest
    Enter                    Motion

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 (“Shift_L” is the keysm 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 should be available in other X documentation. If necessary, you can use the %K notation described below to print out the keysym name for an arbitrary 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>. If a keysym detail is specified then the Shift modifier need not be specified and will be ignored if specified: each keysym already implies a particular state for the shift key.

The command argument to bind is a Tcl command string, 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. If command contains any % characters, then the command string will not be executed directly. Instead, a new command string 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. Valid only for ConfigureNotify events.

|%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, GraphicsExpose, and MappingNotify events.

|%d|

  The detail field from the event. The |%d| is replaced by a string identifying the detail. For EnterNotify, LeaveNotify, FocusIn, and FocusOut events, the string will be one of the following:

      NotifyAncestor            NotifyNonlinearVirtual
      NotifyDetailNone          NotifyPointer
      NotifyInferior            NotifyPointerRoot
      NotifyNonlinear           NotifyVirtual

  For ConfigureRequest events, the substituted string will be one of the following:

      Above                     Opposite
      Below                     TopIf
      BottomIf

  For events other than these, the substituted string is undefined. .RE

|%f|

  The focus field from the event (0 or 1). Valid only for EnterNotify and LeaveNotify events.

|%h|

  The height field from the event. Valid only for Configure, ConfigureNotify, Expose, GraphicsExpose, and ResizeRequest events.

|%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 EnterWindow, FocusIn, FocusOut, and LeaveWindow events.

|%o|

  The override_redirect field from the event. Valid only for CreateNotify, MapNotify, ReparentNotify, and ConfigureNotify events.

|%p|

  The place field from the event, substituted as one of the strings PlaceOnTop or PlaceOnBottom. Valid only for CirculateNotify and CirculateRequest events.

|%s|

  The state field from the event. For ButtonPress, ButtonRelease, EnterNotify, KeyPress, KeyRelease, LeaveNotify, and MotionNotify events, a decimal string is substituted. For VisibilityNotify, one of the strings VisibilityUnobscured, VisibilityPartiallyObscured, and VisibilityFullyObscured is substituted.

|%t|

  The time field from the event. Valid only for events that contain a time field.

|%v|

  The value_mask field from the event. Valid only for ConfigureRequest events.

|%w|

  The width field from the event. Valid only for Configure, ConfigureRequest, Expose, GraphicsExpose, and ResizeRequest events.

|%x|

  The x field from the event. Valid only for events containing an x field.

|%y|

  The y field from the event. Valid only for events containing a y field.

%A

  Substitutes the ASCII character corresponding to the event, or the empty string if the event doesn’t correspond to an ASCII character (e.g. the shift key was pressed). XLookupString does all the work of translating from the event to an ASCII character. Valid only for KeyPress and KeyRelease events.

%B

  The border_width field from the event. Valid only for ConfigureNotify and CreateWindow events.

%D

  The display field from the event. Valid for all event types.

%E

  The send_event field from the event. Valid for all event types.

%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.

%R

  The root window identifier from the event. Valid only for events containing a root field.

%S

  The subwindow window identifier from the event. 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

  The x_root field from the event. If a virtual-root window manager is being used then the substituted value is the corresponding x-coordinate in the virtual root. Valid only for ButtonPress, ButtonRelease, KeyPress, KeyRelease, and MotionNotify events.

%Y

  The y_root field from the event. If a virtual-root window manager is being used then the substituted value is the corresponding y-coordinate in the virtual root. Valid only for ButtonPress, ButtonRelease, KeyPress, KeyRelease, and MotionNotify events.

If the replacement string for a %-replacement contains characters that are interpreted specially by the Tcl parser (such as backslashes or square brackets or spaces) additional backslashes are added during replacement so that the result after parsing is the original replacement string. For example, if command is

    insert %A

and the character typed is an open square bracket, then the command actually executed will be

    insert \e[

This will cause the insert to receive the original replacement string (open square bracket) as its first argument. If the extra backslash hadn’t been added, Tcl would not have been able to parse the command correctly.

At most one binding will trigger for any given X event. If several bindings match the recent events, the most specific binding is chosen and its command will be executed. The following tests are applied, in order, to determine which of several matching sequences is more specific: (a) a binding whose windowSpec names a particular window is more specific than a binding for a class, which is more specific than a binding whose windowSpec is all; (b) a longer sequence (in terms of number of events matched) is more specific than a shorter sequence; (c) an event pattern that specifies a specific button or key is more specific than one that doesn’t; (e) an event pattern that requires a particular modifier is more specific than one that doesn’t require the modifier; (e) an event pattern specifying the Any modifier is less specific than one that doesn’t. 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 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).

When a sequence specified in a bind command contains more than one event pattern, then its command 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 MotionNotify 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 MotionNotify events occur in a row, only the last one is used for purposes of matching binding sequences.

If an error occurs in executing the command for a binding then the tkerror mechanism is used to report the error. The command will be executed at global level (outside the context of any Tcl procedure).

See tkerror.

#### Keywords

form, manual