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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,  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) 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 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 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.
       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.
                      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

       ioctl_console(2), charsets(7)

COLOPHON

       This  page  is  part  of  release  4.15  of  the  Linux man-pages project.  A description of the project,
       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.

Linux                                              2017-09-15                                   CONSOLE_CODES(4)