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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/.