Xterm Control Sequences

Edward Moy
University of California, Berkeley

Revised by
Stephen Gildea
X Consortium (1994)
Thomas Dickey
XFree86 Project (1996-2004)

Definitions

C1 (8-Bit) Control Characters

The xterm program recognizes both 8-bit and 7-bit control characters. It generates 7-bit controls (by default) or 8-bit if S8C1T is enabled. The following pairs of 7-bit and 8-bit control characters are equivalent:

These control characters are used in the vtXXX emulation.

VT100 Mode

Most of these control sequences are standard VT102 control sequences, but there is support for later DEC VT terminals (i.e., VT220, VT320, VT420), as well as ISO 6429 and aixterm color controls. The only VT102 features not supported is auto-repeat, since the only way X provides for this will affect all windows. There are additional control sequences to provide xterm-dependent functions, such as the scrollbar or window size. Where the function is specified by DEC or ISO 6429, the code assigned to it is given in parentheses. The escape codes to designate and invoke character sets are specified by ISO 2022; see that document for a discussion of character sets.

Single-character functions

Controls beginning with ESC (other than those where ESC is part of a 7-bit equivalent to 8-bit C1 controls), ordered by the final character(s).

Application Program-Control functions

Device-Control functions

Functions using CSI , ordered by the final character(s)

Operating System Controls

Privacy Message

PC-Style Function Keys

If xterm does minimal translation of the function keys, it usually does this with a PC-style keyboard, so PC-style function keys result. Sun keyboards are similar to PC keyboards. Both have cursor and scrolling operations printed on the keypad, which duplicate the smaller cursor and scrolling keypads.
X does not predefine NumLock (used for VT220 keyboards) or Alt (used as an extension for the Sun/PC keyboards) as modifiers. These keys are recognized as modifiers when enabled by the numLock resource, or by the DECSET 1 0 3 5 control sequence.
The cursor keys transmit the following escape sequences depending on the mode specified via the DECCKM escape sequence.

The home- and end-keys (unlike PageUp and other keys also on the 6-key editing keypad) are considered "cursor keys" by xterm. Their mode is also controlled by the DECCKM escape sequence:

The application keypad transmits the following escape sequences depending on the mode specified via the DECPNM and DECPAM escape sequences. Use the NumLock key to override the application mode.
Not all keys are present on the Sun/PC keypad (e.g., PF1, Tab), but are supported by the program.

They also provide 12 function keys, as well as a few other special-purpose keys.

Older versions of xterm implement different escape sequences for F1 through F4. These can be activated by setting the oldXtermFKeys resource. However, since they do not correspond to any hardware terminal, they have been deprecated. (The DEC VT220 reserves F1 through F5 for local functions such as Setup).

In normal mode, i.e., a Sun/PC keyboard when the sunKeyboard resource is false, xterm recognizes function key modifiers which are parameters appended before the final character of the control sequence.

For example, shift-F5 would be sent as CSI 1 5 ; 2 ~

If the alwaysUseMods resource is set, the Meta modifier also is recognized, making parameters 9 through 16.

VT220-Style Function Keys

However, xterm is most useful as a DEC VT102 or VT220 emulator. Set the sunKeyboard resource to true to force a Sun/PC keyboard to act like a VT220 keyboard.
The VT102/VT220 application keypad transmits unique escape sequences in application mode, which are distinct from the cursor and scrolling keypad:

The VT220 provides a 6-key editing keypad, which is analogous to that on the PC keyboard. It is not affected by DECCKM or DECPNM/DECPAM:

The VT220 provides 8 additional function keys. With a Sun/PC keyboard, access these keys by Control/F1 for F13, etc.

VT52-Style Function Keys

A VT52 does not have function keys, but it does have a numeric keypad and cursor keys. They differ from the other emulations by the prefix. Also, the cursor keys do not change:

The keypad is similar:

Sun-Style Function Keys

The xterm program provides support for Sun keyboards more directly, by a menu toggle that causes it to send Sun-style function key codes rather than VT220. Note, however, that the sun and VT100 emulations are not really compatible. For example, their wrap-margin behavior differs.
Only function keys are altered; keypad and cursor keys are the same. The emulation responds identically. See the xterm-sun terminfo entry for details.

HP-Style Function Keys

Similarly, xterm can be compiled to support HP keyboards. See the xterm-hp terminfo entry for details.

The Alternate Screen Buffer

Xterm maintains two screen buffers. The normal screen buffer allows you to scroll back to view saved lines of output up to the maximum set by the saveLines resource. The alternate screen buffer is exactly as large as the display, contains no additional saved lines. When the alternate screen buffer is active, you cannot scroll back to view saved lines. Xterm provides control sequences and menu entries for switching between the two.
Most full-screen applications use terminfo or termcap to obtain strings used to start/stop full-screen mode, i.e., smcup and rmcup for terminfo, or the corresponding ti and te for termcap. The titeInhibit resource removes the ti and te strings from the TERMCAP string which is set in the environment for some platforms. That is not done when xterm is built with terminfo libraries because terminfo does not provide the whole text of the termcap data in one piece. It would not work for terminfo anyway, since terminfo data is not passed in environment variables; setting an environment variable in this manner would have no effect on the application’s ability to switch between normal and alternate screen buffers. Instead, the newer private mode controls (such as 1 0 4 9 ) for switching between normal and alternate screen buffers simply disable the switching. They add other features such as clearing the display for the same reason: to make the details of switching independent of the application that requests the switch.

Mouse Tracking

The VT widget can be set to send the mouse position and other information on button presses. These modes are typically used by editors and other full-screen applications that want to make use of the mouse.

There are six mutually exclusive modes. One is DEC Locator mode, enabled by the DECELR CSI P s ; P s ´z control sequence, and is not described here (control sequences are summarized above). The remaining five modes are each enabled (or disabled) by a different parameter in DECSET CSI ? P m h or DECRST CSI ? P m l control sequence.

Manifest constants for the parameter values are defined in xcharmouse.h as follows:

The motion reporting modes are strictly xterm extensions, and are not part of any standard, though they are analogous to the DEC VT200 DECELR locator reports.

Parameters (such as pointer position and button number) for all mouse tracking escape sequences generated by xterm encode numeric parameters in a single character as value+32. For example, ! specifies the value 1. The upper left character position on the terminal is denoted as 1,1.

X10 compatibility mode sends an escape sequence only on button press, encoding the location and the mouse button pressed. It is enabled by specifying parameter 9 to DECSET. On button press, xterm sends CSI M C b C x C y (6 characters). C b is button−1. C x and C y are the x and y coordinates of the mouse when the button was pressed.

Normal tracking mode sends an escape sequence on both button press and release. Modifier key (shift, ctrl, meta) information is also sent. It is enabled by specifying parameter 1000 to DECSET. On button press or release, xterm sends CSI M C b C x C y . The low two bits of C b encode button information: 0=MB1 pressed, 1=MB2 pressed, 2=MB3 pressed, 3=release. The next three bits encode the modifiers which were down when the button was pressed and are added together: 4=Shift, 8=Meta, 16=Control. Note however that the shift and control bits are normally unavailable because xterm uses the control modifier with mouse for popup menus, and the shift modifier is used in the default translations for button events. The Meta modifier recognized by xterm is the mod1 mask, and is not necessarily the "Meta" key (see xmodmap). C x and C y are the x and y coordinates of the mouse event, encoded as in X10 mode.

Wheel mice may return buttons 4 and 5. Those buttons are represented by the same event codes as buttons 1 and 2 respectively, except that 64 is added to the event code. Release events for the wheel buttons are not reported.

Mouse hilite tracking notifies a program of a button press, receives a range of lines from the program, highlights the region covered by the mouse within that range until button release, and then sends the program the release coordinates. It is enabled by specifying parameter 1001 to DECSET. Highlighting is performed only for button 1, though other button events can be received. Warning: use of this mode requires a cooperating program or it will hang xterm. On button press, the same information as for normal tracking is generated; xterm then waits for the program to send mouse tracking information. All X events are ignored until the proper escape sequence is received from the pty: CSI P s ; P s ; P s ; P s ; P s T . The parameters are func, startx, starty, firstrow, and lastrow. func is non-zero to initiate hilite tracking and zero to abort. startx and starty give the starting x and y location for the highlighted region. The ending location tracks the mouse, but will never be above row firstrow and will always be above row lastrow. (The top of the screen is row 1.) When the button is released, xterm reports the ending position one of two ways: if the start and end coordinates are valid text locations: CSI t C x C y . If either coordinate is past the end of the line: CSI T C x C y C x C y C x C y . The parameters are startx, starty, endx, endy, mousex, and mousey. startx, starty, endx, and endy give the starting and ending character positions of the region. mousex and mousey give the location of the mouse at button up, which may not be over a character.

Button-event tracking is essentially the same as normal tracking, but xterm also reports button-motion events. Motion events are reported only if the mouse pointer has moved to a different character cell. It is enabled by specifying parameter 1002 to DECSET. On button press or release, xterm sends the same codes used by normal tracking mode. On button-motion events, xterm adds 32 to the event code (the third character, C b ). The other bits of the event code specify button and modifier keys as in normal mode. For example, motion into cell x,y with button 1 down is reported as CSI M @ C x C y . ( @ = 32 + 0 (button 1) + 32 (motion indicator) ). Similarly, motion with button 3 down is reported as CSI M B C x C y . ( B = 32 + 2 (button 3) + 32 (motion indicator) ).

Any-event mode is the same as button-event mode, except that all motion events are reported, even if no mouse button is down. It is enabled by specifying 1003 to DECSET.

Tektronix 4014 Mode

Most of these sequences are standard Tektronix 4014 control sequences. Graph mode supports the 12-bit addressing of the Tektronix 4014. The major features missing are the write-through and defocused modes. This document does not describe the commands used in the various Tektronix plotting modes but does describe the commands to switch modes.

VT52 Mode

Parameters for cursor movement are at the end of the ESC Y escape sequence. Each ordinate is encoded in a single character as value+32. For example, ! is 1. The screen coodinate system is 0-based.