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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/IEC 6429 / ANSI X3.64 terminal
       controls, plus certain private-mode sequences for changing the color palette, character-set mapping,  and
       so  on.   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)
       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)
       SUB (0x1A, ^Z)
              abort 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 %              Start sequence selecting character set
       ESC % @               Select default (ISO/IEC 646 / ISO/IEC 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 (followed by one of B, 0, U, K, as below)
       ESC ( B            Select default (ISO/IEC 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      Operating System Command prefix.
       ESC ] R            Reset palette.
       ESC ] P            Set palette, with parameter given in 7 hexadecimal digits nrrggbb after the final P.
                          Here n is the color (0–15), and rrggbb indicates the red/green/blue values (0–255).

       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 current line.
       X   ECH       Erase the indicated # of characters on 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 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 Select Graphic 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)
       3          set italic (since Linux 2.6.22; 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 underline; before Linux 4.17, this value set normal intensity (as is done in many other
                  terminals)
       22         set normal intensity
       23         italic off (since Linux 2.6.22)
       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         256/24-bit foreground color follows, shoehorned into 16 basic colors (before Linux 3.16: set
                  underscore on, set default foreground color)
       39         set default foreground color (before Linux 3.16: 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
       48         256/24-bit background color follows, shoehorned into 8 basic colors
       49         set default background color
       90..97     set foreground to bright versions of 30..37
       100..107   set background, same as 40..47 (bright not supported)

       Commands 38 and 48 require further arguments:

       ;5;x       256 color: values 0..15 are IBGR (black, red, green, ... white), 16..231 a 6x6x6  color  cube,
                  232..255 a grayscale ramp
       ;2;r;g;b   24-bit color, r/g/b components are in the range 0..255

       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; 8–15 = bright versions of 0–7.

       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.
       ESC [ 15 ]          Bring the previous console to the front (since Linux 2.6.0).
       ESC [ 16 ; n ]      Set the cursor blink interval in milliseconds (since Linux 4.2).

   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 make only 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 terminal 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.

       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 Linux 2.0.23, CSI is broken, and NUL is not ignored inside escape sequences.

       Some older kernel versions (after Linux 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

       ioctl_console(2), charsets(7)