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CONSOLE_CODES(4)           Linux Programmer's Manual          CONSOLE_CODES(4)



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 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 trans-
       formed 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 Uni-
       code (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 cur-
       rently 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  capabili-
       ties.   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).

   Linux Console Controls
       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

       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, and
              if LF/NL (new-line mode) is set also a carriage return;

       CR (0x0D, ^M) gives a carriage return;

       SO (0x0E, ^N) activates the G1 character set;

       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     T{  DEC private
       identification. The kernel returns the string  ESC [ ?  6  c,  claiming
       that it is a VT102.  T} ESC 7     DECSC     T{ Save current state (cur-
       sor coordinates, attributes, character sets pointed at by G0, G1).   T}
       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 map-
       ping - 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  T{ (Should
       be: Operating system command) ESC ] P nrrggbb: set palette, with param-
       eter  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 T}

       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   characters.
       A    CUU  Move  cursor up the indicated # of rows.  B    CUD  Move cur-
       sor 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, col-
       umn.  g    TBC  Without parameter: clear tab stop at the current  posi-
       tion.             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, separated by  semi-
       colons.   An empty parameter (between semicolons or string initiator or
       terminator) is interpreted as a zero.

       l l.  param     result 0    reset  all  attributes  to  their  defaults
       1    set  bold  2    set  half-bright  (simulated with color on a color
       display) 4    T{ set underscore (simulated with color on a  color  dis-
       play) (the colors used to simulate dim or underline are set using ESC ]
       ...)  T} 5    set blink 7    set reverse video 10   T{  reset  selected
       mapping, display control flag, and toggle meta flag (ECMA-48 says "pri-
       mary font").  T} 11   T{ select null mapping, set display control flag,
       reset  toggle  meta  flag  (ECMA-48  says  "first alternate font").  T}
       12   T{ select null mapping, set display control flag, set toggle  meta
       flag  (ECMA-48  says  "second  alternate  font").  The toggle meta flag
       causes the high bit of a byte to be toggled before  the  mapping  table
       translation  is done.  T} 21   set normal intensity (ECMA-48 says "dou-
       bly  underlined")  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  fore-
       ground  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 fore-
       ground 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

       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(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
              DECTECM (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.  Colors 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 interval in minutes.

   Character Sets
       The kernel knows about 4 translations of bytes into console-screen sym-
       bols.  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), respec-
       tively.   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
       The mouse tracking facility is intended to return  (1)xterm(1)-compati-
       ble  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.

       The  mouse  tracking  escape  sequences  generated  by  xterm(1) 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(1) 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(1) 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 modi-
       fiers 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).

   Comparisons With Other Terminals
       Many different terminal types are described, like the Linux console, as
       being  "VT100-compatible".   Here  we  discuss  differences between the
       Linux console and the two most important  others,  the  DEC  VT102  and
       xterm(1).

       Control-character handling

       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(1) 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 console:

       l l l.  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(1) (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 US-ASCII, respectively.

       The user can configure xterm(1) to respond  to  VT220-specific  control
       sequences, and it will identify itself as a VT52, VT100, and up depend-
       ing on the way it is configured and initialized.

       It accepts ESC ] (OSC) for the setting of certain resources.  In  addi-
       tion  to  the ECMA-48 string terminator (ST), xterm(1) accepts a BEL to
       terminate an OSC string.  These are a few of the OSC control  sequences
       recognized by xterm(1):

       l l.  ESC ] 0 ; txt ST    Set icon name and window title to txt.  ESC ]
       1 ; txt ST     Set icon name to txt.  ESC ] 2 ;  txt  ST    Set  window
       title to txt.  ESC ] 4 ; num; txt ST    Set ANSI color num to txt.  ESC
       ] 10 ; txt ST    Set dynamic text color to txt.   ESC  ]  4  6  ;  name
       ST Change  log  file  to name (normally disabled      by a compile-time
       option) ESC ] 5 0 ; fn ST   Set font to fn.

       It recognizes the following with slightly modified meaning (saving more
       state, behaving closer to VT100/VT220):

       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            xterm(1)'s  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 also recognizes ESC % and provides a more complete UTF-8 implementa-
       tion than Linux console.

       CSI Sequences

       Old  versions of xterm(1), for example, from X11R5, interpret the blink
       SGR as a bold SGR.  Later versions which implemented ANSI  colors,  for
       example,  XFree86  3.1.2A  in 1995, improved this by allowing the blink
       attribute to be displayed as a color.  Modern versions of xterm  imple-
       ment  blink  SGR  as  blinking  text and still allow colored text as an
       alternate rendering of SGRs.  Stock X11R6 versions  did  not  recognize
       the  color-setting  SGRs  until the X11R6.8 release, which incorporated
       XFree86 xterm.  All ECMA-48 CSI sequences recognized by Linux are  also
       recognized  by  xterm,  however xterm(1) implements several ECMA-48 and
       DEC control sequences not recognized by Linux.

       The xterm(1) program recognizes all of the DEC Private  Mode  sequences
       listed  above,  but none of the Linux private-mode sequences.  For dis-
       cussion of xterm(1)'s own private-mode sequences, refer  to  the  Xterm
       Control Sequences document by Edward Moy, Stephen Gildea, and Thomas E.
       Dickey available with the X distribution.  That document, though terse,
       is much longer than this manual page.  For a chronological overview,

           http://invisible-island.net/xterm/xterm.log.html

       details changes to xterm.

       The vttest program

           http://invisible-island.net/vttest/

       demonstrates many of these control sequences.  The xterm(1) source dis-
       tribution also contains sample scripts which exercise other features.

NOTES
       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.

       Some  older  kernel  versions  (after  2.0)  interpret  8-bit   control
       sequences.   These  "C1  controls"  use  codes  between  128 and 159 to
       replace ESC [, ESC ] and similar two-byte control sequence  initiators.
       There  are  fragments  of  that in modern kernels (either overlooked or
       broken by changes to support UTF-8), but the implementation  is  incom-
       plete and should be regarded as unreliable.

       Linux  "private  mode" sequences do not follow the rules in ECMA-48 for
       private mode control sequences.  In particular, those ending with ]  do
       not  use  a  standard  terminating  character.   The  OSC (set palette)
       sequence is a greater problem, since xterm(1) may interpret this  as  a
       control  sequence  which requires a string terminator (ST).  Unlike the
       setterm(1) sequences which will be ignored (since they are invalid con-
       trol sequences), the palette sequence will make xterm(1) appear to hang
       (though pressing the return-key will fix that).  To accommodate  appli-
       cations  which  have been hardcoded to use Linux control sequences, set
       the xterm(1) resource brokenLinuxOSC to true.

       An older version of this document implied  that  Linux  recognizes  the
       ECMA-48 control sequence for invisible text.  It is ignored.

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

COLOPHON
       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-01-01                  CONSOLE_CODES(4)