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console_codes - Linux console escape and control sequences
The Linux console implements a large subset of the VT102 and ECMA-48/ISO
6429/ANSI X3.64 terminal controls, plus certain private-mode sequences for
changing the color palette, character-set mapping, etc. In the tabular
descriptions below, the second column gives ECMA-48 or DEC mnemonics (the
latter if prefixed with DEC) for the given function. Sequences without a
mnemonic are neither ECMA-48 nor VT102.
After all the normal output processing has been done, and a stream of characters
arrives at the console driver for actual printing, the first thing that
happens is a translation from the code used for processing to the code used
for printing.
If the console is in UTF-8 mode, then the incoming bytes are first assembled
into 16-bit Unicode codes. Otherwise each byte is transformed according to the
current mapping table (which translates it to a Unicode value). See the
CHARACTER SETS section below for discussion.
In the normal case, the Unicode value is converted to a font index, and this is
stored in video memory, so that the corresponding glyph (as found in video
ROM) appears on the screen. Note that the use of Unicode (and the design of
the PC hardware) allows us to use 512 different glyphs simultaneously.
If the current Unicode value is a control character, or we are currently
processing an escape sequence, the value will treated specially. Instead of
being turned into a font index and rendered as a glyph, it may trigger cursor
movement or other control functions. See the LINUX CONSOLE CONTROLS section
below for discussion.
It is generally not good practice to hard-wire terminal controls into programs.
Linux supports a
terminfo(5) database of terminal capabilities. Rather
than emitting console escape sequences by hand, you will almost always want to
use a terminfo-aware screen library or utility such as
ncurses(3),
tput(1), or
reset(1).
This section describes all the control characters and escape sequences that
invoke special functions (i.e. anything other than writing a glyph at the
current cursor location) on the Linux console.
A character is a control character if (before transformation according to the
mapping table) it has one of the 14 codes 00 (NUL), 07 (BEL), 08 (BS), 09
(HT), 0a (LF), 0b (VT), 0c (FF), 0d (CR), 0e (SO), 0f (SI), 18 (CAN), 1a
(SUB), 1b (ESC), 7f (DEL). One can set a `display control characters' mode
(see below), and allow 07, 09, 0b, 18, 1a, 7f to be displayed as glyphs. On
the other hand, in UTF-8 mode all codes 00-1f are regarded as control
characters, regardless of any `display control characters' mode.
If we have a control character, it is acted upon immediately and then discarded
(even in the middle of an escape sequence) and the escape sequence continues
with the next character. (However, ESC starts a new escape sequence, possibly
aborting a previous unfinished one, and CAN and SUB abort any escape
sequence.) The recognized control characters are BEL, BS, HT, LF, VT, FF, CR,
SO, SI, CAN, SUB, ESC, DEL, CSI. They do what one would expect:
BEL (0x07,
^G) beeps;
BS (0x08, ^H)
backspaces one column (but not past the beginning of the line);
HT (0x09, ^I)
goes to the next tab stop or to the end of the line if there is no earlier tab
stop;
LF (0x0A,
^J), VT (0x0B, ^K) and FF (0x0C, ^L) all give a linefeed;
CR (0x0D, ^M)
gives a carriage return;
SO (0x0E, ^N)
activates the G1 character set, and if LF/NL (new line mode) is set also a
carriage return;
SI (0x0F, ^O)
activates the G0 character set;
CAN (0x18,
^X) and SUB (0x1A, ^Z) interrupt escape sequences;
ESC (0x1B,
^[) starts an escape sequence;
DEL (0x7F) is
ignored;
CSI (0x9B) is
equivalent to ESC [.
| ESC c |
RIS |
Reset. |
| ESC D |
IND |
Linefeed. |
| ESC E |
NEL |
Newline. |
| ESC H |
HTS |
Set tab stop at current column. |
| ESC M |
RI |
Reverse linefeed. |
| ESC Z |
DECID |
DEC private identification. The kernel |
|
|
returns the string ESC [ ? 6 c, claiming |
|
|
that it is a VT102. |
| ESC 7 |
DECSC |
Save current state (cursor coordinates, |
|
|
attributes, character sets pointed at by G0, G1). |
| ESC 8 |
DECRC |
Restore state most recently saved by ESC 7. |
| ESC [ |
CSI |
Control sequence introducer |
| ESC % |
|
Start sequence selecting character set |
| ESC % @ |
|
Select default (ISO 646 / ISO 8859-1) |
| ESC % G |
|
Select UTF-8 |
| ESC % 8 |
|
Select UTF-8 (obsolete) |
| ESC # 8 |
DECALN |
DEC screen alignment test - fill screen with E's. |
| ESC ( |
|
Start sequence defining G0 character set |
| ESC ( B |
|
Select default (ISO 8859-1 mapping) |
| ESC ( 0 |
|
Select vt100 graphics mapping |
| ESC ( U |
|
Select null mapping - straight to character
ROM |
| ESC ( K |
|
Select user mapping - the map that is loaded
by |
|
|
the utility mapscrn(8). |
| ESC ) |
|
Start sequence defining G1 |
|
|
(followed by one of B, 0, U, K, as above). |
| ESC > |
DECPNM |
Set numeric keypad mode |
| ESC = |
DECPAM |
Set application keypad mode |
| ESC ] |
OSC |
(Should be: Operating system command) |
|
|
ESC ] P nrrggbb: set palette, with parameter |
|
|
given in 7 hexadecimal digits after the final P :-(. |
|
|
Here n is the color (0-15), and rrggbb indicates |
|
|
the red/green/blue values (0-255). |
|
|
ESC ] R: reset palette |
CSI (or ESC [) is followed by a sequence of parameters, at most NPAR (16), that
are decimal numbers separated by semicolons. An empty or absent parameter is
taken to be 0. The sequence of parameters may be preceded by a single question
mark.
However, after CSI [ (or ESC [ [) a single character is read and this entire
sequence is ignored. (The idea is to ignore an echoed function key.)
The action of a CSI sequence is determined by its final character.
| @ |
ICH |
Insert the indicated # of blank characters. |
| A |
CUU |
Move cursor up the indicated # of rows. |
| B |
CUD |
Move cursor down the indicated # of rows. |
| C |
CUF |
Move cursor right the indicated # of columns. |
| D |
CUB |
Move cursor left the indicated # of columns. |
| E |
CNL |
Move cursor down the indicated # of rows, to column 1. |
| F |
CPL |
Move cursor up the indicated # of rows, to column 1. |
| G |
CHA |
Move cursor to indicated column in current row. |
| H |
CUP |
Move cursor to the indicated row, column (origin at 1,1). |
| J |
ED |
Erase display (default: from cursor to end of display). |
|
|
ESC [ 1 J: erase from start to cursor. |
|
|
ESC [ 2 J: erase whole display. |
| K |
EL |
Erase line (default: from cursor to end of line). |
|
|
ESC [ 1 K: erase from start of line to cursor. |
|
|
ESC [ 2 K: erase whole line. |
| L |
IL |
Insert the indicated # of blank lines. |
| M |
DL |
Delete the indicated # of lines. |
| P |
DCH |
Delete the indicated # of characters on the current line. |
| X |
ECH |
Erase the indicated # of characters on the current line. |
| a |
HPR |
Move cursor right the indicated # of columns. |
| c |
DA |
Answer ESC [ ? 6 c: `I am a VT102'. |
| d |
VPA |
Move cursor to the indicated row, current column. |
| e |
VPR |
Move cursor down the indicated # of rows. |
| f |
HVP |
Move cursor to the indicated row, column. |
| g |
TBC |
Without parameter: clear tab stop at the current position. |
|
|
ESC [ 3 g: delete all tab stops. |
| h |
SM |
Set Mode (see below). |
| l |
RM |
Reset Mode (see below). |
| m |
SGR |
Set attributes (see below). |
| n |
DSR |
Status report (see below). |
| q |
DECLL |
Set keyboard LEDs. |
|
|
ESC [ 0 q: clear all LEDs |
|
|
ESC [ 1 q: set Scroll Lock LED |
|
|
ESC [ 2 q: set Num Lock LED |
|
|
ESC [ 3 q: set Caps Lock LED |
| r |
DECSTBM |
Set scrolling region; parameters are top and bottom row. |
| s |
? |
Save cursor location. |
| u |
? |
Restore cursor location. |
| ` |
HPA |
Move cursor to indicated column in current row. |
The ECMA-48 SGR sequence ESC [ <parameters> m sets display attributes.
Several attributes can be set in the same sequence.
| par |
result |
| 0 |
reset all attributes to their defaults |
| 1 |
set bold |
| 2 |
set half-bright (simulated with color on a color display) |
| 4 |
set underscore (simulated with color on a color display) |
|
(the colors used to simulate dim or underline are set |
|
using ESC ] ...) |
| 5 |
set blink |
| 7 |
set reverse video |
| 10 |
reset selected mapping, display control flag, |
|
and toggle meta flag. |
| 11 |
select null mapping, set display control flag, |
|
reset toggle meta flag. |
| 12 |
select null mapping, set display control flag, |
|
set toggle meta flag. (The toggle meta flag |
|
causes the high bit of a byte to be toggled |
|
before the mapping table translation is done.) |
| 21 |
set normal intensity (this is not compatible with ECMA-48) |
| 22 |
set normal intensity |
| 24 |
underline off |
| 25 |
blink off |
| 27 |
reverse video off |
| 30 |
set black foreground |
| 31 |
set red foreground |
| 32 |
set green foreground |
| 33 |
set brown foreground |
| 34 |
set blue foreground |
| 35 |
set magenta foreground |
| 36 |
set cyan foreground |
| 37 |
set white foreground |
| 38 |
set underscore on, set default foreground color |
| 39 |
set underscore off, set default foreground color |
| 40 |
set black background |
| 41 |
set red background |
| 42 |
set green background |
| 43 |
set brown background |
| 44 |
set blue background |
| 45 |
set magenta background |
| 46 |
set cyan background |
| 47 |
set white background |
| 49 |
set default background color |
- ESC [ 3 h
- DECCRM (default off): Display control chars.
- ESC [ 4 h
- DECIM (default off): Set insert mode.
- ESC [ 20 h
- LF/NL (default off): Automatically follow echo of LF, VT or
FF with CR.
- ESC [ 5 n
- Device status report (DSR): Answer is ESC [ 0 n (Terminal
OK).
- ESC [ 6 n
- Cursor position report (CPR): Answer is ESC [ y ;
x R, where x,y is the cursor location.
These are not described in ECMA-48. We list the Set Mode sequences; the Reset
Mode sequences are obtained by replacing the final `h' by `l'.
- ESC [ ? 1 h
- DECCKM (default off): When set, the cursor keys send an ESC
O prefix, rather than ESC [.
- ESC [ ? 3 h
- DECCOLM (default off = 80 columns): 80/132 col mode switch.
The driver sources note that this alone does not suffice; some user-mode
utility such as resizecons(8) has to change the hardware registers
on the console video card.
- ESC [ ? 5 h
- DECSCNM (default off): Set reverse-video mode.
- ESC [ ? 6 h
- DECOM (default off): When set, cursor addressing is
relative to the upper left corner of the scrolling region.
- ESC [ ? 7 h
- DECAWM (default on): Set autowrap on. In this mode, a
graphic character emitted after column 80 (or column 132 of DECCOLM is on)
forces a wrap to the beginning of the following line first.
- ESC [ ? 8 h
- DECARM (default on): Set keyboard autorepreat on.
- ESC [ ? 9 h
- X10 Mouse Reporting (default off): Set reporting mode to 1
(or reset to 0) - see below.
- ESC [ ? 25 h
- DECCM (default on): Make cursor visible.
- ESC [ ? 1000 h
- X11 Mouse Reporting (default off): Set reporting mode to 2
(or reset to 0) - see below.
The following sequences are neither ECMA-48 nor native VT102. They are native to
the Linux console driver. Colors are in SGR parameters: 0 = black, 1 = red, 2
= green, 3 = brown, 4 = blue, 5 = magenta, 6 = cyan, 7 = white.
| ESC [ 1 ; n ] |
Set color n as the underline color |
| ESC [ 2 ; n ] |
Set color n as the dim color |
| ESC [ 8 ] |
Make the current color pair the default attributes. |
| ESC [ 9 ; n ] |
Set screen blank timeout to n minutes. |
| ESC [ 10 ; n ] |
Set bell frequency in Hz. |
| ESC [ 11 ; n ] |
Set bell duration in msec. |
| ESC [ 12 ; n ] |
Bring specified console to the front. |
| ESC [ 13 ] |
Unblank the screen. |
| ESC [ 14 ; n ] |
Set the VESA powerdown interval in minutes. |
The kernel knows about 4 translations of bytes into console-screen symbols. The
four tables are: a) Latin1 -> PC, b) VT100 graphics -> PC, c) PC ->
PC, d) user-defined.
There are two character sets, called G0 and G1, and one of them is the current
character set. (Initially G0.) Typing ^N causes G1 to become current, ^O
causes G0 to become current.
These variables G0 and G1 point at a translation table, and can be changed by
the user. Initially they point at tables a) and b), respectively. The
sequences ESC ( B and ESC ( 0 and ESC ( U and ESC ( K cause G0 to point at
translation table a), b), c) and d), respectively. The sequences ESC ) B and
ESC ) 0 and ESC ) U and ESC ) K cause G1 to point at translation table a), b),
c) and d), respectively.
The sequence ESC c causes a terminal reset, which is what you want if the screen
is all garbled. The oft-advised "echo ^V^O" will only make G0
current, but there is no guarantee that G0 points at table a). In some
distributions there is a program
reset(1) that just does "echo
^[c". If your terminfo entry for the console is correct (and has an entry
rs1=\Ec), then "tput reset" will also work.
The user-defined mapping table can be set using
mapscrn(8). The result of
the mapping is that if a symbol c is printed, the symbol s = map[c] is sent to
the video memory. The bitmap that corresponds to s is found in the character
ROM, and can be changed using
setfont(8).
The mouse tracking facility is intended to return xterm-compatible mouse status
reports. Because the console driver has no way to know the device or type of
the mouse, these reports are returned in the console input stream only when
the virtual terminal driver receives a mouse update ioctl. These ioctls must
be generated by a mouse-aware user-mode application such as the
gpm(8)
daemon.
Parameters for all mouse tracking escape sequences generated by
xterm
encode numeric parameters in a single character as
value+040. For
example, `!' is 1. The screen coordinate system is 1-based.
The X10 compatibility mode sends an escape sequence on button press encoding the
location and the mouse button pressed. It is enabled by sending ESC [ ? 9 h
and disabled with ESC [ ? 9 l. On button press,
xterm sends ESC [ M
bxy (6 characters). Here
b is button-1, and
x and
y are the x and y coordinates of the mouse when the button was pressed.
This is the same code the kernel also produces.
Normal tracking mode (not implemented in Linux 2.0.24) sends an escape sequence
on both button press and release. Modifier information is also sent. It is
enabled by sending ESC [ ? 1000 h and disabled with ESC [ 1000 l. On button
press or release,
xterm sends ESC [ M
bxy. The low two bits of
b encode button information: 0=MB1 pressed, 1=MB2 pressed, 2=MB3
pressed, 3=release. The upper bits encode what modifiers were down when the
button was pressed and are added together: 4=Shift, 8=Meta, 16=Control. Again
x and
y are the x and y coordinates of the mouse event. The
upper left corner is (1,1).
Many different terminal types are described, like the Linux console, as being
`VT100-compatible'. Here we discuss differences vbetween the Linux console an
the two most important others, the DEC VT102 and
xterm(1).
The vt102 also recognized the following control characters:
NUL (0x00)
was ignored;
ENQ (0x05)
triggered an answerback message;
DC1 (0x11,
^Q, XON) resumed transmission;
DC3 (0x13,
^S, XOFF) caused vt100 to ignore (and stop transmitting) all codes except XOFF
and XON.
VT100-like DC1/DC3 processing may be enabled by the tty driver.
The
xterm program (in vt100 mode) recognizes the control characters BEL,
BS, HT, LF, VT, FF, CR, SO, SI, ESC.
VT100 console sequences not implemented on the Linux console:
| ESC N |
SS2 |
Single shift 2. (Select G2 character set for the next |
|
|
character only.) |
| ESC O |
SS3 |
Single shift 3. (Select G3 character set for the next |
|
|
character only.) |
| ESC P |
DCS |
Device control string (ended by ESC \) |
| ESC X |
SOS |
Start of string. |
| ESC ^ |
PM |
Privacy message (ended by ESC \) |
| ESC \ |
ST |
String terminator |
| ESC * ... |
|
Designate G2 character set |
| ESC + ... |
|
Designate G3 character set |
The program
xterm (in vt100 mode) recognizes ESC c, ESC # 8, ESC >,
ESC =, ESC D, ESC E, ESC H, ESC M, ESC N, ESC O, ESC P ... ESC ESC Z (it
answers ESC [ ? 1 ; 2 c, `I am a vt100 with advanced video option') and ESC ^
... ESC with the same meanings as indicated above. It accepts ESC (,
ESC ), ESC *, ESC + followed by 0, A, B for the DEC special character and line
drawing set, UK, and USASCII, respectively. It accepts ESC ] for the setting
of certain resources:
| ESC ] 0 ; txt BEL |
Set icon name and window title to txt. |
| ESC ] 1 ; txt BEL |
Set icon name to txt. |
| ESC ] 2 ; txt BEL |
Set window title to txt. |
| ESC ] 4 6 ; name BEL |
Change log file to name (normally disabled |
|
by a compile-time option) |
| ESC ] 5 0 ; fn BEL |
Set font to fn. |
It recognizes the following with slightly modified meaning:
| ESC 7 DECSC |
Save cursor |
|
| ESC 8 DECRC |
Restore cursor |
|
It also recognizes
| ESC F |
|
Cursor to lower left corner of screen (if enabled by |
|
|
the hpLowerleftBugCompat resource) |
| ESC l |
|
Memory lock (per HP terminals). |
|
|
Locks memory above the cursor. |
| ESC m |
|
Memory unlock (per HP terminals). |
| ESC n |
LS2 |
Invoke the G2 character set. |
| ESC o |
LS3 |
Invoke the G3 character set. |
| ESC | |
LS3R |
Invoke the G3 character set as GR. |
|
|
Has no visible effect in xterm. |
| ESC } |
LS2R |
Invoke the G2 character set as GR. |
|
|
Has no visible effect in xterm. |
| ESC ~ |
LS1R |
Invoke the G1 character set as GR. |
|
|
Has no visible effect in xterm. |
It does not recognize ESC % ...
The
xterm program (as of XFree86 3.1.2G) does not recognize the blink or
invisible-mode SGRs. Stock X11R6 versions do not recognize the color-setting
SGRs. All other ECMA-48 CSI sequences recognized by Linux are also recognized
by
xterm, and vice-versa.
The
xterm program will recognize all of the DEC Private Mode sequences
listed above, but none of the Linux private-mode sequences. For discussion of
xterm's own private-mode sequences, refer to the
Xterm Control
Sequences document by Edward Moy and Stephen Gildea, available with the X
distribution.
In 2.0.23, CSI is broken, and NUL is not ignored inside escape sequences.
console(4),
console_ioctl(4),
charsets(7)
