ANSI escape code

"ANSI code" redirects here. For other uses, see ANSI (disambiguation).

ANSI escape sequences are a standard for in-band signaling to control the cursor location, color, and other options on video text terminals. Certain sequences of bytes, most starting with Esc and '[', are embedded into the text, which the terminal looks for and interprets as commands, not as character codes.

ANSI sequences were introduced in the 1970s to replace vendor-specific sequences and became widespread in the computer equipment market by the early 1980s. They were used by the nascent bulletin board systems to offer improved displays compared to earlier systems lacking cursor movement, a primary reasons they became a standard adopted by all manufacturers.

Although hardware text terminals have become increasingly rare in the 21st century, the relevance of the ANSI standard persists because most terminal emulators interpret at least some of the ANSI escape sequences in output text. One notable exception was the Win32 console of Microsoft Windows before Windows 10 update TH2.

History

Almost all manufacturers of video terminals added vendor-specific escape sequences to perform operations such as placing the cursor at arbitrary positions on the screen. One example is the VT52 terminal, which allowed the cursor to be placed at an x,y location on the screen by sending the ESC character, a y character, and then two characters representing with numerical values equal to the x,y location plus 32 (thus starting at the ASCII space character and avoiding the control characters).

As these sequences were different for different terminals, elaborate libraries such as termcap and utilities such as tput had to be created so programs could use the same API to work with any terminal. In addition many of these terminals required sending numbers (such as row and column) as the binary values of the characters; for some programming languages, and for systems that did not use ASCII internally, it was often difficult or impossible to turn a number into the correct character.

The ANSI standard attempted to address these problems by making a command set that all terminals would use and requiring all numeric information to be transmitted as ASCII numbers. The first standard in the series was ECMA-48, adopted in 1976. It was a continuation of a series of character coding standards, the first one being ECMA-6 from 1965, a 7-bit standard from which ISO 646 originates. The name "ANSI escape sequence" dates from 1979 when ANSI adopted ANSI X3.64. The ANSI X3L2 committee collaborated with the ECMA committee TC 1 to produce nearly identical standards. These two standards were merged into an international standard, ISO 6429. In 1994, ANSI withdrew its standard in favor of the international standard.

The first popular video terminal to support these sequences was the Digital VT100, introduced in 1978. This model was very successful in the market, which sparked a variety of VT100 clones, among the earliest and most popular of which was the much more affordable Zenith Z-19 in 1979. Others included the Qume QVT-108, Televideo TVI-970, Wyse WY-99GT as well as optional "VT100" or "VT103" or "ANSI" modes with varying degrees of compatibility on many other brands. The popularity of these gradually led to more and more software (especially bulletin board systems) assuming the escape sequences worked, leading to almost all new terminals and emulator programs supporting them.

In 1981, ANSI X3.64 was adopted for use in the US government by FIPS publication 86. Later, the US government stopped duplicating industry standards, so FIPS pub. 86 was withdrawn.

ECMA-48 has been updated several times and is currently at its 5th edition, from 1991. It is also adopted by ISO and IEC as standard ISO/IEC 6429.

Platform support

The widespread use of ANSI by bulletin boards and online services led to almost universal platform support by the mid 1980s. In most cases this took the form of a terminal emulator (such as xterm on Unix or the OS X Terminal or ZTerm on MacOS and many communication programs for the IBM PC), although there was increasing support in the standard text output of many operating systems.

Unix and the AmigaOS all included some ANSI support in the OS, which led to widespread use of ANSI by programs running on those platforms. Unix-like operating systems could produce ANSI codes through libraries such as termcap and curses used by many pieces of software to update the display. These libraries are supposed to support non-ANSI terminals as well, but this is so rarely tested nowadays that they are unlikely to work. Many games and shell scripts (such as colored prompts) directly write the ANSI sequences and thus cannot be used on a terminal that does not interpret them.

AmigaOS not only interprets ANSI code sequences for text output to the screen, the AmigaOS printer driver also interprets them (with extensions proprietary to AmigaOS) and translates them into the codes required for the particular printer that is actually attached.

In spite of its popularity, ANSI codes were not universally supported. Support was not built-in on the original "classic" Mac OS, while the Atari ST used the command system adapted from the VT52 with some expansions for color support.

Windows and DOS

MS-DOS 1.x did not support the ANSI or any other escape sequences. Only a few control characters (BEL, CR, LF, BS) were interpreted by the underlying BIOS, making it almost impossible to do any kind of full-screen application. Any display effects had to be done with BIOS calls, which were notoriously slow, or by directly manipulating the IBM PC hardware.

DOS 2.0 introduced the ability to add a device driver for the ANSI escape sequences – the de facto standard being ANSI.SYS, but others like ANSI.COM, NANSI.SYS and ANSIPLUS.EXE are used as well (these are considerably faster as they bypass the BIOS). Slowness and the fact that it was not installed by default made software rarely take advantage of it; instead, applications continued to directly manipulate the hardware to get the text display needed. ANSI.SYS and similar drivers continued to work in Windows 9x up to Windows Me, and in NT-derived systems for 16-bit legacy programs executing under the NTVDM.

The Win32 console did not support ANSI escape sequences at all. Some replacements or additions for the console window such as JP Software's TCC (formerly 4NT), Michael J. Mefford's ANSI.COM, Jason Hood's ANSICON and Maximus5's ConEmu interpreted ANSI escape sequences printed by programs. A Python package internally interpreted ANSI escape sequences in text being printed, translating them to calls to manipulate the color and cursor position, to make it easier to port Python code using ANSI to Windows.

In 2016 with Windows 10 "Threshold 2" Microsoft unexpectedly started supporting ANSI escape sequences in the console app, making the porting of software from (or remote access to) Unix much easier.

Escape sequences

Sequences have different lengths. All sequences start with the ASCII character ESC (27 / hex 0x1B), followed by a second byte in the range 0x40–0x5F (ASCII @A–Z[\]^_).

The standard says that in 8-bit environments these two-byte sequences can be merged into single byte in the 0x80–0x9F range (for details see C1 control codes). However on modern devices those codes are often used for other purposes, such as parts of UTF-8 or for CP-1252 characters, so only the 2-byte sequence is used.

Other C0 codes besides ESC — commonly BEL, BS, CR, LF, FF, TAB, VT, SO, and SI — may produce similar or identical effects to some control sequences when output.

Some ANSI escape sequences (not a complete list)

Sequence	C1	Name	Effect
ESC N	0x8e	SS2 – Single Shift Two	Select a single character from one of the alternative character sets. In xterm, SS2 selects the G2 character set, and SS3 selects the G3 character set.
ESC O	0x8f	SS3 – Single Shift Three
ESC P	0x90	DCS – Device Control String	Controls a device. In xterm, uses of this sequence include defining User-Defined Keys, and requesting or setting Termcap/Terminfo data.
ESC [	0x9b	CSI - Control Sequence Introducer	Most of the useful sequences, see next section. Ends at ASCII 64 to 126 (@ to ~ / hex 0x40 to 0x7E).
ESC \	0x9c	ST – String Terminator	Terminates strings in other controls (including APC, DCS, OSC, PM, and SOS).
ESC ]	0x9d	OSC – Operating System Command	Starts a control string for the operating system to use. OSC sequences are similar to CSI sequences, but are not limited to integer arguments. In general, these control sequences are terminated by ST. In xterm, they may also be terminated by BEL. For example, in xterm, the window title can be set by OSC 0;this is the window title BEL.
ESC X	0x98	SOS – Start of String	Takes an argument of a string of text, terminated by ST. The uses for these string control sequences are defined by the application or privacy discipline. These functions are not implemented and the arguments are ignored by xterm.
ESC ^	0x9e	PM – Privacy Message
ESC _	0x9f	APC – Application Program Command
ESC c		RIS – Reset to Initial State	Resets the device to its original state. This may include (if applicable): reset graphic rendition, clear tabulation stops, reset to default font, and more.

Pressing special keys on the keyboard, as well as outputting many xterm CSI, DCS, or OSC sequences, often produces a CSI, DCS, or OSC sequence, sent from the terminal to the computer as though the user typed it.

CSI sequences

The ESC [ is followed by any number (including none) of "parameter bytes" in the range 0x30–0x3F (ASCII 0–9:;<=>?), then by any number of "intermediate bytes" in the range 0x20–0x2F (ASCII space and !"#$%&'()*+,-./), then finally by a single "final byte" in the range 0x40–0x7E (ASCII @A–Z[\]^_`a–z{|}~).

All sequences in common use just use the parameters as a series of semicolon-separated numbers (for instance 1;2;3). Missing numbers are treated as 0 (for instance 1;;3 acts like the middle number is 0, and no parameters at all in ESC[m acts like a 0 reset code). Some sequences (such as CUU) treat 0 as 1 in order to make the missing parameters useful. Intermediate bytes seem to not be used.

A subset of arrangements was declared "private" so that terminal manufacturers could insert their own sequences without conflicting with the standard. This includes use of the parameter bytes <=>? or the final bytes 0x70–0x7F (p–z{|}~). A popular example of a private code is the sequences CSI?25h and CSI?25l for the VT320 to turn the cursor on/off.

The behavior of the terminal is undefined in the case where a CSI sequence contains any character outside of the range 0x20–0x7E. These illegal characters are either C0 control characters (the range 0–0x1F), DEL (0x7F), or bytes with the high bit set. Possible responses are to ignore the byte, to process it immediately, and furthermore whether to continue with the CSI sequence, to abort it immediately, or to ignore the rest of it.

Some ANSI control sequences (not a complete list)

Code	Name	Effect
CSI n A	CUU – Cursor Up	Moves the cursor $n$ (default 1) cells in the given direction. If the cursor is already at the edge of the screen, this has no effect.
CSI n B	CUD – Cursor Down
CSI n C	CUF – Cursor Forward
CSI n D	CUB – Cursor Back
CSI n E	CNL – Cursor Next Line	Moves cursor to beginning of the line $n$ (default 1) lines down. (not ANSI.SYS)
CSI n F	CPL – Cursor Previous Line	Moves cursor to beginning of the line $n$ (default 1) lines up. (not ANSI.SYS)
CSI n G	CHA – Cursor Horizontal Absolute	Moves the cursor to column $n$ (default 1). (not ANSI.SYS)
CSI n ; m H	CUP – Cursor Position	Moves the cursor to row $n$, column $m$. The values are 1-based, and default to 1 (top left corner) if omitted. A sequence such as CSI ;5H is a synonym for CSI 1;5H as well as CSI 17;H is the same as CSI 17H and CSI 17;1H
CSI n J	ED – Erase in Display	Clears part of the screen. If $n$ is 0 (or missing), clear from cursor to end of screen. If $n$ is 1, clear from cursor to beginning of the screen. If $n$ is 2, clear entire screen (and moves cursor to upper left on DOS ANSI.SYS). If $n$ is 3, clear entire screen and delete all lines saved in the scrollback buffer (this feature was added for xterm and is supported by other terminal applications).
CSI n K	EL – Erase in Line	Erases part of the line. If $n$ is zero (or missing), clear from cursor to the end of the line. If $n$ is one, clear from cursor to beginning of the line. If $n$ is two, clear entire line. Cursor position does not change.
CSI n S	SU – Scroll Up	Scroll whole page up by $n$ (default 1) lines. New lines are added at the bottom. (not ANSI.SYS)
CSI n T	SD – Scroll Down	Scroll whole page down by $n$ (default 1) lines. New lines are added at the top. (not ANSI.SYS)
CSI n ; m f	HVP – Horizontal Vertical Position	Same as CUP
CSI n m	SGR – Select Graphic Rendition	Sets SGR parameters, including text color. After CSI can be zero or more parameters separated with semicolon. If none, CSI m is treated as CSI 0 m (reset / normal).
CSI 5i	AUX Port On	Enable aux serial port usually for local serial printer
CSI 4i	AUX Port Off	Disable aux serial port usually for local serial printer
CSI 6n	DSR – Device Status Report	Reports the cursor position (CPR) to the application as (as though typed at the keyboard) ESC[n;mR, where $n$ is the row and $m$ is the column.)
CSI s	SCP – Save Cursor Position	Saves the cursor position.
CSI u	RCP – Restore Cursor Position	Restores the cursor position.

SGR (Select Graphic Rendition) parameters

Code	Effect	Note
0	Reset / Normal	all attributes off
1	Bold or increased intensity
2	Faint (decreased intensity)	Not widely supported.
3	Italic	Not widely supported. Sometimes treated as inverse.
4	Underline
5	Slow Blink	less than 150 per minute
6	Rapid Blink	MS-DOS ANSI.SYS; 150+ per minute; not widely supported
7	reverse video	swap foreground and background colors
8	Conceal	Not widely supported.
9	Crossed-out	Characters legible, but marked for deletion. Not widely supported.
10	Primary(default) font
11–19	Alternative font	Select alternative font $n-10$
20	Fraktur	hardly ever supported
21	Bold off or Double Underline	Bold off not widely supported; double underline hardly ever supported.
22	Normal color or intensity	Neither bold nor faint
23	Not italic, not Fraktur
24	Underline off	Not singly or doubly underlined
25	Blink off
27	Inverse off
28	Reveal	conceal off
29	Not crossed out
30–37	Set foreground color	See color table below
38	Set foreground color	Next arguments are 5;n or 2;r;g;b, see below
39	Default foreground color	implementation defined (according to standard)
40–47	Set background color	See color table below
48	Set background color	Next arguments are 5;n or 2;r;g;b, see below
49	Default background color	implementation defined (according to standard)
51	Framed
52	Encircled
53	Overlined
54	Not framed or encircled
55	Not overlined
60	ideogram underline or right side line	hardly ever supported
61	ideogram double underline or double line on the right side
62	ideogram overline or left side line
63	ideogram double overline or double line on the left side
64	ideogram stress marking
65	ideogram attributes off	reset the effects of all of 60–64
90–97	Set bright foreground color	aixterm (not in standard)
100–107	Set bright background color	aixterm (not in standard)

Colors

3/4 bit

The original specification only had 8 colors, and just gave them names. The SGR parameters 30-37 selected the foreground color, while 40-47 selected the background. Quite a few terminals implemented "bold" (SGR code 1) as a brighter color rather than a different font, thus providing 8 additional foreground colors. Usually you could not get these as background colors, though sometimes inverse video (SGR code 7) would allow that. Examples: to get black letters on white background use ESC[30;47m, to get red use ESC[31m, to get bright red use ESC[1;31m. To reset colors to their defaults, use ESC[39;49m (not supported on some terminals), or reset all attributes with ESC[0m. Later terminals added the ability to directly specify the "bright" colors with 90-97 and 100-107.

When hardware started using 8-bit DACs several pieces of software assigned 24-bit color numbers to these names. The chart below shows values sent to the DAC for some common hardware and software.

Name	FG Code	BG Code	VGA	CMD	Terminal.app	PuTTY	mIRC	xterm	X	Ubuntu
Black	30	40	0,0,0							1,1,1
Red	31	41	170,0,0	128,0,0	194,54,33	187,0,0	127,0,0	205,0,0	255,0,0	222,56,43
Green	32	42	0,170,0	0,128,0	37,188,36	0,187,0	0,147,0	0,205,0	0,255,0	57,181,74
Yellow	33	43	170,85,0	128,128,0	173,173,39	187,187,0	252,127,0	205,205,0	255,255,0	255,199,6
Blue	34	44	0,0,170	0,0,128	73,46,225	0,0,187	0,0,127	0,0,238	0,0,255	0,111,184
Magenta	35	45	170,0,170	128,0,128	211,56,211	187,0,187	156,0,156	205,0,205	255,0,255	118,38,113
Cyan	36	46	0,170,170	0,128,128	51,187,200	0,187,187	0,147,147	0,205,205	0,255,255	44,181,233
White	37	47	170,170,170	192,192,192	203,204,205	187,187,187	210,210,210	229,229,229	255,255,255	204,204,204
Bright Black	1;30	100	85,85,85	128,128,128	129,131,131	85,85,85	127,127,127	127,127,127		128,128,128
Bright Red	1;31	101	255,85,85	255,0,0	252,57,31	255,85,85	255,0,0	255,0,0		255,0,0
Bright Green	1;32	102	85,255,85	0,255,0	49,231,34	85,255,85	0,252,0	0,255,0	144,238,144	0,255,0
Bright Yellow	1;33	103	255,255,85	255,255,0	234,236,35	255,255,85	255,255,0	255,255,0	255,255,224	255,255,0
Bright Blue	1;34	104	85,85,255	0,0,255	88,51,255	85,85,255	0,0,252	92,92,255	173,216,230	0,0,255
Bright Magenta	1;35	105	255,85,255	255,0,255	249,53,248	255,85,255	255,0,255	255,0,255		255,0,255
Bright Cyan	1;36	106	85,255,255	0,255,255	20,240,240	85,255,255	0,255,255	0,255,255	224,255,255	0,255,255
Bright White	1;37	107	255,255,255	255,255,255	233,235,235	255,255,255	255,255,255	255,255,255		255,255,255

8-bit

As 256-color lookup tables became common on graphic cards, escape sequences were added to select from a pre-defined set of 256 colors:

   ESC[ … 38;5;<n> … m Select foreground color
   ESC[ … 48;5;<n> … m Select background color
   0x00-0x07:  standard colors (as in ESC [ 30–37 m)
   0x08-0x0F:  high intensity colors (as in ESC [ 90–97 m)
   0x10-0xE7:  6 × 6 × 6 cube (216 colors): 16 + 36 × r + 6 × g + b (0 ≤ r, g, b ≤ 5)
   0xE8-0xFF:  grayscale from black to white in 24 steps

256-color mode — foreground: ESC[38;5;#m   background: ESC[48;5;#m
Standard colors																		High-intensity colors
0   1   2   3   4   5   6   7   8   9  10 11 12 13 14 15
216 colors
16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50	51
52	53	54	55	56	57	58	59	60	61	62	63	64	65	66	67	68	69	70	71	72	73	74	75	76	77	78	79	80	81	82	83	84	85	86	87
88	89	90	91	92	93	94	95	96	97	98	99	100	101	102	103	104	105	106	107	108	109	110	111	112	113	114	115	116	117	118	119	120	121	122	123
124	125	126	127	128	129	130	131	132	133	134	135	136	137	138	139	140	141	142	143	144	145	146	147	148	149	150	151	152	153	154	155	156	157	158	159
160	161	162	163	164	165	166	167	168	169	170	171	172	173	174	175	176	177	178	179	180	181	182	183	184	185	186	187	188	189	190	191	192	193	194	195
196	197	198	199	200	201	202	203	204	205	206	207	208	209	210	211	212	213	214	215	216	217	218	219	220	221	222	223	224	225	226	227	228	229	230	231
Grayscale colors
232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255

24-bit

As "true color" graphic cards with 16 to 24 bits of color became common, Xterm, KDE's Konsole, as well as all libvte based terminals (including GNOME Terminal) support ISO-8613-3 24-bit foreground and background color setting

   ESC[ … 38;2;<r>;<g>;<b> … m Select RGB foreground color
   ESC[ … 48;2;<r>;<g>;<b> … m Select RGB background color

The ITU's T.416 Information technology - Open Document Architecture (ODA) and interchange format: Character content architectures which was adopted as ISO/IEC International Standard 8613-6 gives an alternative version that seems to be less supported:

   ESC[ … 38:2:<r>:<g>:<b>:<unused>:<CS tolerance>:<Color-Space: 0="CIELUV"; 1="CIELAB">m Select RGB foreground color
   ESC[ … 48:2:<r>:<g>:<b>:<unused>:<CS tolerance>:<Color-Space: 0="CIELUV"; 1="CIELAB">m Select RGB background color

Note that this uses the otherwise reserved ':' character to separate the sub-options which may have been a source of confusion for real-world implementations. It also documents using '3' as the second parameter to specify colors using a Cyan-Magenta-Yellow scheme and '4' for a Cyan-Magenta-Yellow-Black one, the latter using the position marked as "unused" in the above examples for the Black component.

Xterm allows also setting colors by X11 color names using

   ESC]10;<foreground>BEL
   ESC]11;<background>BEL

where <foreground> and <background> are text, and BEL is the ASCII BEL character (code 7). The closing bracket instead of an opening bracket reveals that it belongs to the operating system control commands.

Examples

CSI 2 J — This clears the screen and, on some devices, locates the cursor to the y,x position 1,1 (upper left corner).

CSI 32 m — This makes text green. On MS-DOS, normally the green would be dark, dull green, so you may wish to enable Bold with the sequence CSI 1 m which would make it bright green, or combined as CSI 32 ; 1 m. MS-DOS ANSI.SYS uses the Bold state to make the character Bright; also the Blink state can be set (via INT 10, AX 1003h, BL 00h) to render the Background in the Bright mode. MS-DOS ANSI.SYS does not support SGR codes 90–97 and 100–107 directly.

CSI 0 ; 6 8 ; "DIR" ; 13 p — This reassigns the key F10 to send to the keyboard buffer the string "DIR" and ENTER, which in the DOS command line would display the contents of the current directory. (MS-DOS ANSI.SYS only) This was sometimes used for ANSI bombs. This is a private-use code (as indicated by the letter p), using a non-standard extension to include a string-valued parameter. Following the letter of the standard would consider the sequence to end at the letter D.

CSI s — This saves the cursor position. Using the sequence CSI u will restore it to the position. Say the current cursor position is 7(y) and 10(x). The sequence CSI s will save those two numbers. Now you can move to a different cursor position, such as 20(y) and 3(x), using the sequence CSI 20 ; 3 H or CSI 20 ; 3 f. Now if you use the sequence CSI u the cursor position will return to 7(y) and 10(x). Some terminals require the DEC sequences ESC 7 / ESC 8 instead which is more widely supported.

Example of use in shell scripting

ANSI escape codes are often used in UNIX and UNIX-like terminals to provide syntax highlighting. For example, on compatible terminals, the following list command color-codes file and directory names by type.

ls --color

Users can employ escape codes in their scripts by including them as part of standard output or standard error. For example, the following GNU sed command embellishes the output of the make command by displaying lines containing words starting with "WARN" in reverse video and words starting with "ERR" in bright yellow on a dark red background (letter case is ignored). The representations of the codes are highlighted.

make 2>&1 | sed -e 's/.*\bWARN.*/\x1b[7m&\x1b[0m/i' -e 's/.*\bERR.*/\x1b[93;41 m&\x1b[0m/i'

The following Bash function flashes the terminal (by alternately sending reverse and normal video mode codes) until the user presses a key.

flasher () { while true; do printf \\e[?5h; sleep 0.1; printf \\e[?5l; read -s -n1 -t1 && break; done; }

This can be used to alert a programmer when a lengthy command terminates, such as with make ; flasher .

printf \\033c

This will reset the console, similar to the command reset on modern Linux systems; however it should work even on older Linux systems and on other (non-Linux) UNIX variants.

Invalid and ambiguous sequences in use

• The Linux console uses OSC P n rr gg bb to change the palette, which, if hard-coded into an application, may hang other terminals. However, appending ST will be ignored by Linux and form a proper, ignorable sequence for other terminals.
• On the Linux console, certain function keys generate sequences of the form CSI [ char. The CSI sequence should terminate on the [.
• Old versions of Terminator generate SS3 1; modifiers char when F1–F4 are pressed with modifiers. The faulty behavior was copied from GNOME Terminal.
• xterm replies CSI row ; column R if asked for cursor position and CSI 1 ; modifiers R if the F3 key is pressed with modifiers, which collide in the case of row == 1. This can be avoided by using the ? private modifier, which will be reflected in the response.
• many terminals prepend ESC to any character that is typed with the alt key down. This creates ambiguity for uppercase letters and symbols @[\]^_, which would form C1 codes.
• Konsole generates SS3 modifiers char when F1–F4 are pressed with modifiers.

See also

• ANSI art
• Control character
• Advanced Video Attribute Terminal Assembler and Recreator (AVATAR)
• ISO/IEC JTC 1/SC 2

External links

• Standard ECMA-48, Control Functions For Coded Character Sets. (5th edition, June 1991), European Computer Manufacturers Association, Geneva 1991 (also published by ISO and IEC as standard ISO/IEC 6429)
• vt100.net DEC Documents
• ANSI.SYS -- ansi terminal emulation escape sequences at the Wayback Machine (archived 6 February 2006)
• Xterm / Escape Sequences
• AIXterm / Escape Sequences
• A collection of escape sequences for terminals that are vaguely compliant with ECMA-48 and friends.
• ANSI Escape Sequences
• ITU-T Rec. T.416 (03/93) Information technology – Open Document Architecture (ODA) and interchange format: Character content architectures