Linux - console_codes

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Linux - console_codes

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
       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

   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.


       @   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
       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.


       param   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 (ECMA-48 says "primary font").

       11      select null mapping, set display control flag, reset tog-
           gle meta flag (ECMA-48 says "first alternate font").
       12      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 tog-
           gled before the mapping table translation is done.
       21      set normal intensity (ECMA-48 says "doubly 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 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
       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.

       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.

       The 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  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  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:

       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 US-ASCII, respectively.

       The  user  can  configure  xterm     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 accepts a BEL to ter-
       minate  an  OSC    string.      These are a few of the OSC control sequences
       recognized by xterm:

       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):

       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
              xterm’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.
       ESC }   LS2R   Invoke the G2 character set as GR.
       ESC ~   LS1R   Invoke the G1 character set as GR.

       It also recognizes ESC % and provides a more complete UTF-8 implementa-
       tion than Linux console.

   CSI Sequences
       Old versions of xterm, e.g., from X11R5, interpret the blink SGR     as  a
       bold  SGR.  Later versions which implemented ANSI colors, e.g., XFree86
       3.1.2A in 1995, improved this by allowing the  blink  attribute    to  be
       displayed  as a color.  Modern versions of xterm implement 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 implements several ECMA-48 and DEC control sequences  not
       recognized by Linux.

       The  xterm  program  recognizes    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, 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 source distri-
       bution also contains sample scripts which exercise other features.

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.

       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 may interpret this as a con-
       trol sequence which requires a string terminator (ST).  Unlike the set-
       term  sequences    which  will be ignored (since they are invalid control
       sequences), the palette sequence will make xterm appear to hang (though
       pressing     the  return-key  will fix that).  To accommodate applications
       which have been hardcoded to use Linux control sequences, set the xterm
       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)



Linux                  2006-05-29              CONSOLE_CODES(4)

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