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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 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).

   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

       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.
                     ESC [ 3 J: erase whole display including scroll-back
                                buffer (since Linux 3.0).
       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 semicolons.   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
               toggle 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
               toggled 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 autorepeat 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  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
       The mouse tracking  facility  is  intended  to  return  xterm(1)-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.

       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 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).

   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:

       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 depending on the way it is configured and
       initialized.

       It accepts ESC ] (OSC) for the setting of certain resources.  In addition 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):

       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(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 implementation 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 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(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 discussion 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 distribution 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 incomplete
       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 control sequences), the
       palette  sequence  will  make xterm(1) 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(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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.