unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (Debian-3.1)
Page:
Section:
Apropos / Subsearch:
optional field

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;

       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 identi-
       fication. The kernel           returns the string  ESC [ ? 6 c,  claim-
       ing            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  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  (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

   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.

       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 (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, dis-
       play  control  flag,       and toggle meta flag.  11   select null map-
       ping,  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  fore-
       ground  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 fore-
       ground color 39   set underscore  off,  set  default  foreground  color
       40   set  black background 41   set red background 42   set green back-
       ground 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
              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.  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 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 con-
       sole 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  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  vbetween  the
       Linux  console  an  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  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 (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:

       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  (nor-
       mally  disabled       by a compile-time option) ESC ] 5 0 ; fn BEL  Set
       font to fn.

       It recognizes the following with slightly modified meaning:

       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 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 dis-
       cussion 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.

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



Linux                             1996-10-31                  CONSOLE_CODES(4)