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NAME    [Toc]    [Back]

       console_codes - Linux console escape and control sequences

DESCRIPTION    [Toc]    [Back]

       The   Linux  console  implements  a  large  subset  of  the  VT102  and
       ECMA-48/ISO 6429/ANSI X3.64 terminal controls,  plus  certain  privatemode
  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

       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.

   Control characters    [Toc]    [Back]
       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

       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    [Toc]    [Back]
       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).
       ESC 8	 DECRC	  Restore most recently saved state.
       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 (0-16), and rrggbb indicates
			  the red/green/blue values (0-255).
			  ESC ] R: reset palette

   ECMA-48 CSI sequences    [Toc]    [Back]
       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

       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.

   ECMA-48 Set Graphics Rendition    [Toc]    [Back]
       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

   ECMA-48 Mode Switches    [Toc]    [Back]
       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    [Toc]    [Back]
       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

       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 usermode
 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.

   Linux Console Private CSI Sequences    [Toc]    [Back]
       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.

CHARACTER SETS    [Toc]    [Back]

       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).

MOUSE TRACKING    [Toc]    [Back]

       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

   Control-character handling    [Toc]    [Back]
       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.

   Escape sequences    [Toc]    [Back]
       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 % ...

   CSI Sequences    [Toc]    [Back]
       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 Con-
       trol Sequences document by Edward Moy  and  Stephen  Gildea,  available
       with the X distribution.

BUGS    [Toc]    [Back]

       In  2.0.23,  CSI  is  broken,  and  NUL	is  not  ignored inside escape

SEE ALSO    [Toc]    [Back]

       console(4), console_ioctl(4), charsets(7)

Linux				  1996-10-31		      CONSOLE_CODES(4)
[ Back ]
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