CONSOLE_CODES(S) Linux Programmer's Manual CONSOLE_CODES(S) NAME console_codes - Linux console escape and control sequences DESCRIPTION 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 trans- lation 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 CON- SOLE CONTROLS section below for discussion. It is generally not good practice to hard-wire terminal controls into programs. Linux supports a terminfo(o) 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(s), tput(t), or reset(t). LINUX CONSOLE CONTROLS This section describes all the control characters and escape sequences that invoke special functions (i.e. any- thing other than writing a glyph at the current cursor location) on the Linux console. Control characters A character is a control character if (before transforma- tion 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 charac- ters, regardless of any `display control characters' mode. If we have a control character, it is acted upon immedi- ately 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- but not CSI-sequences l l l. 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 graph- ics mapping ESC ( U Select null mapping - straight to character ROM ESC ( K Select user mapping - the map that is loaded by the util- ity mapscrn(n). ESC ) Start sequence defining G1 (followed by one of B, 0, U, K, as above). ESC > DECPNM Set numeric keypad mode ESC = DEC- PAM Set application keypad mode ESC ] OSC (Should be: Operating system command) ESC ] P nrrggbb: set palette, with parameter given in 7 hexadeci- mal digits after the final P :-(. Here n is the color (0-16), and rrggbb indicates the red/green/blue values (0-255). ESC ] R: reset palette ECMA-48 CSI sequences 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. l l l. @ ICH Insert the indicated # of blank charac- ters. 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 indi- cated row, column (origin at 1,1). J ED Erase dis- play (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 indi- cated row, current column. e VPR Move cursor down the indicated # of rows. f HVP Move cursor to the indi- cated 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. ECMA-48 Set Graphics Rendition The ECMA-48 SGR sequence ESC [ <parameters> m sets display attributes. Several attributes can be set in the same sequence. l l. 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 (simu- lated 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 fore- ground 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 back- ground 49 set default background color ECMA-48 Mode Switches 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. ECMA-48 Status Report Commands 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. DEC Private Mode (DECSET/DECRST) sequences. 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(s) 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. Linux Console Private CSI Sequences The following sequences are neither ECMA-48 nor native VT102. They are native to the Linux console driver. Col- ors are in SGR parameters: 0 = black, 1 = red, 2 = green, 3 = brown, 4 = blue, 5 = magenta, 6 = cyan, 7 = white. l l. 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 inter- val in minutes. CHARACTER SETS The kernel knows about 4 translations of bytes into con- sole-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 distribu- tions there is a program reset(t) 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 map- scrn(n). 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(t). MOUSE TRACKING 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(m) daemon. Parameters for all mouse tracking escape sequences gener- ated by xterm encode numeric parameters in a single char- acter 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 dis- abled 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 pro- duces. 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 send- ing 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=Con- trol. Again x and y are the x and y coordinates of the mouse event. The upper left corner is (1,1). COMPARISONS WITH OTHER TERMINALS Many different terminal types are described, like the Linux console, as being `VT100-compatible'. Here we dis- cuss differences vbetween the Linux console an the two most important others, the DEC VT102 and xterm(m). Control-character handling The vt102 also recognized the following control charac- ters: 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. Escape sequences VT100 console sequences not implemented on the Linux con- sole: l l l. ESC N SS2 Single shift 2. (Select G2 charac- ter 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 spe- cial character and line drawing set, UK, and USASCII, respectively. It accepts ESC ] for the setting of certain resources: l l. 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 mean- ing: l l l. ESC 7 DECSC Save cursor ESC 8 DECRC Restore cursor It also recognizes l l l. 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 % ... CSI Sequences The xterm program (as of XFree86 3.1.2G) does not recog- nize the blink or invisible-mode SGRs. Stock X11R6 ver- sions do not recognize the color-setting SGRs. All other ECMA-48 CSI sequences recognized by Linux are also recog- nized by xterm, and vice-versa. The xterm program will recognize all of the DEC Private Mode sequences listed above, but none of the Linux pri- vate-mode sequences. For discussion of xterm's own pri- vate-mode sequences, refer to the Xterm Control Sequences document by Edward Moy and Stephen Gildea, available with the X distribution. NOTE ESC 8 (DECRC) is not able to restore the character set changed with ESC %. BUGS In 2.0.23, CSI is broken, and NUL is not ignored inside escape sequences. SEE ALSO console(e), console_ioctl(l), charsets(s) Linux 1996-10-31 CONSOLE_CODES(S)