ANSI escape code
In computing, ANSI escape code (or escape sequences) is the method of in-band signaling to control formatting, color, and other output options on video text terminals. To encode this formatting information, it embeds certain sequences of bytes into the text, which have to be interpreted specially, not as codes of characters. Although hardware text terminals have become increasingly rare in the 21st century, the relevance of this standard persists because most terminal emulators interpret at least some of the ANSI escape sequences in the output text. One notable exception is the win32 console component of Microsoft Windows.
Almost all manufacturers of video terminals added vendor-specific escape sequences to do operations such as placing the cursor at arbitrary positions on the screen. As these sequences were all different, elaborate libraries such as termcap had to be created so programs could use the same API for all of them. In addition, most designs required sending numbers (such as row & 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 first standard for ANSI escape sequences was ECMA-48, adopted in 1976. It was a continuation of a series of character coding standards, the first one being ECMA-6 from 1961, a 7-bit standard from which ASCII originates. ECMA-48 has been updated several times and the current edition is the 5th from 1991. It is also adopted by ISO and IEC as standard ISO/IEC 6429. The name "ANSI escape sequence" dates from 1981 when ANSI adopted ECMA-48 as the standard ANSI X3.64 (and later, in 1997, withdrew it).
The first popular video terminal to support these sequences was the Digital VT100 introduced in 1978, which sparked a variety of "clones", among the earliest and most popular of which was the much more affordable Zenith Z-19 in 1979. 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.
Most terminal emulators running on Unix-like systems (such as xterm and the OS X Terminal) interpret ANSI escape sequences. The Linux console (the text seen when X is not running) also interprets them. Terminal programs for Microsoft Windows designed to show text from an outside source (a serial port, modem, or socket) also interpret them. Some support for text from local programs on Windows is offered through alternate command processors such as JP Software's TCC (formerly 4NT), Michael J. Mefford's ANSI.COM, and Jason Hood's ansicon.
Many Unix console applications (e.g., ls, grep, Vim, and Emacs) can generate them. Utility programs such as tput output them, as well as in low-level programming libraries, such as termcap or terminfo, or a higher-level library such as curses.
Windows and DOS
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 (or far more often 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.
The Win32 console does not natively support ANSI escape sequences at all. Software such as ANSICON can act as a wrapper around the standard Win32 console and add support for ANSI escape sequences. Otherwise software must manipulate the console with the ioctl-like Console API interlaced with the text output. Some software internally interprets ANSI escape sequences in text being printed and translates them to these calls.
Escape sequences start with the character ESC (ASCII decimal 27/hex 0x1B/octal 033). For two character sequences, the second character is in the range ASCII 64 to 95 (@ to _). However, most of the sequences are more than two characters, and start with the characters ESC and [ (left bracket). This sequence is called CSI for Control Sequence Introducer (or Control Sequence Initiator). The final character of these sequences is in the range ASCII 64 to 126 (@ to ~).
There is a single-character CSI (155/0x9B/0233) as well. The ESC+[ two-character sequence is more often used than the single-character alternative, for details see C0 and C1 control codes. Only the two-character sequence is recognized by devices that support just ASCII (7-bit bytes) or devices that support 8-bit bytes but use the 0x80–0x9F control character range for other purposes. On terminals that use UTF-8 encoding, both forms take 2 bytes (CSI in UTF-8 is 0xC2, 0x9B)[discuss] but the ESC+[ sequence is clearer.
Though some encodings use multiple bytes per character, the following discussion is restricted to ASCII characters, and so assumes each character is directly represented by a single byte.
Note: 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.
- ESC N = SS2
- ESC O = SS3
- Select a single character from one of the alternate character sets.
- ESC ^ = PM
- ESC _ = APC
- These each take a single string of text, terminated by ST (ESC \ ). They are ignored by xterm.
- ESC P = DCS
- Device control string,
- ESC ] = OSC
- Operating system command — these are similar to CSI, but not limited to integer arguments. Because they are frequently used, in many cases BEL is an acceptable alternative to ST. E.g., in xterm, the window title can be set by: "OSC0;this is the window titleBEL"
Note: 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.
The general structure of most ANSI escape sequences is
CSI [private mode character(s?)] n1 ; n2... [trailing intermediate character(s?)] letter. The final byte, modified by private mode characters and trailing intermediate characters, specifies the command. The numbers are optional parameters. The default value used for omitted parameters varies with the command, but is usually 1 or 0. If trailing parameters are omitted, the trailing semicolons may also be omitted.
The final byte is technically any character in the range 64 to 126 (hex 0x40 to 0x7e, ASCII @ to ~), and may be modified with leading intermediate bytes in the range 32 to 47 (hex 0x20 to 0x2f).
The colon (0x3a) is the only character not a part of the general sequence; it was left for future standardization, so any sequence containing it should be ignored. Although multiple private mode characters or trailing intermediates are permitted, there are no such known usages.
If there are any leading private mode characters, the main body of the sequence could theoretically contain any order of characters 0x30 – 0x3f instead of a well-formed semicolon-separated list of numbers, but all known terminals are nice and just use them as a flag. Sequences are also private if the final byte is in the range 112 to 126 (hex 0x70 to 0x7e, ASCII p to ~).
The existence of a C0 control, DEL (0x7f), or a high characters is undefined.[clarification needed] Typically, implementations will either cancel the sequence or execute the control and then continue parsing the CSI sequence.[clarification needed]
|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. (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 Display||Clears part of the screen. If n is zero (or missing), clear from cursor to end of screen. If n is one, clear from cursor to beginning of the screen. If n is two, clear entire screen (and moves cursor to upper left on DOS ANSI.SYS).
|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 and Vertical Position||Moves the cursor to row n, column m. Both default to 1 if omitted. 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 ;. With no parameters, CSI m is treated as CSI 0 m (reset / normal), which is typical of most of the ANSI escape sequences.
|CSI 6 n||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.|
|CSI ?25l||DECTCEM||Hides the cursor. (Note: the trailing character is lowercase L.)|
|CSI ?25h||DECTCEM||Shows the cursor.|
|0||Reset / Normal||all attributes off|
|1||Bold or increased intensity|
|2||Faint (decreased intensity)||not widely supported|
|3||Italic: on||not widely supported. Sometimes treated as inverse.|
|5||Blink: Slow||less than 150 per minute|
|6||Blink: Rapid||MS-DOS ANSI.SYS; 150 per minute or more; not widely supported|
|7||Image: Negative||inverse or reverse; swap foreground and background (reverse video)|
|8||Conceal||not widely supported|
|9||Crossed-out||Characters legible, but marked for deletion. Not widely supported.|
|11–19||n-th alternate font||Select the n-th alternate font. 14 being the fourth alternate font, up to 19 being the 9th alternate font.|
|20||Fraktur||hardly ever supported|
|21||Bold: off or Underline: Double||bold off not widely supported, double underline hardly ever|
|22||Normal color or intensity||neither bold nor faint|
|23||Not italic, not Fraktur|
|24||Underline: None||not singly or doubly underlined|
|29||Not crossed out|
|30–37||Set text color (foreground)||30 + x, where x is from the color table below|
|38||Set xterm-256 text color (foreground)[dubious ]||next arguments are 5;x where x is color index (0..255)|
|39||Default text color (foreground)||implementation defined (according to standard)|
|40–47||Set background color||40 + x, where x is from the color table below|
|48||Set xterm-256 background color||next arguments are 5;x where x is color index (0..255)|
|49||Default background color||implementation defined (according to standard)|
|54||Not framed or encircled|
|60||ideogram underline or right side line||hardly ever supported|
|61||ideogram double underline or double line on the right side||hardly ever supported|
|62||ideogram overline or left side line||hardly ever supported|
|63||ideogram double overline or double line on the left side||hardly ever supported|
|64||ideogram stress marking||hardly ever supported|
|90–99||Set foreground text color, high intensity||aixterm (not in standard)|
|100–109||Set background color, high intensity||aixterm (not in standard)|
Text colors (and SGR parameters in general) are manipulated using
CSI n1 [;n2 [; ...]] m sequences, where each
n2, ... is an SGR parameter as shown above. Thus, for instance, you use codes
30+i to specify foreground color,
40+i to specify background color, where
i is the number in the desired color's column header in the table below. The following examples can be used with the
printf utility, where
\x1b[ implements the CSI: To switch the foreground color to black, use
\x1b[30m; to switch to red, use
\x1b[31m; utilizing the "bold" parameter, gray would be
\x1b[30;1m; to get bold red, use
\x1b[31;1m. To reset colors to their defaults, use
\x1b[39;49m (or reset all attributes with
There are two other color standards CSS/HTML standard colors and X Window colors which standardize both the color names and associated RGB color values, but the escape sequence standard only specifies the color names, not RGB values. The chart below shows default RGB assignments for some common terminal programs, together with the CSS and the X-Window colors for these color names.
|Color name||Standard VGA colors||Windows XP
|Normal||Black||0, 0, 0||0, 0, 0||0, 0, 0||0, 0, 0||0, 0, 0||0, 0, 0||0, 0, 0|
|Red||170, 0, 0||128, 0, 0||194, 54, 33||187, 0, 0||205, 0, 0||255, 0, 0||255, 0, 0|
|Green||0, 170, 0||0, 128, 0||37, 188, 36||0, 187, 0||0, 205, 0||0, 255, 0||0, 128, 0|
|Brown/yellow||170, 85, 0||128, 128, 0||173, 173, 39||187, 187, 0||205, 205, 0||255, 255, 0||255, 255, 0|
|Blue||0, 0, 170||0, 0, 128||73, 46, 225||0, 0, 187||0, 0, 238||0, 0, 255||0, 0, 255|
|Magenta||170, 0, 170||128, 0, 128||211, 56, 211||187, 0, 187||205, 0, 205||255, 0, 255||255, 0, 255|
|Cyan||0, 170, 170||0, 128, 128||51, 187, 200||0, 187, 187||0, 205, 205||0, 255, 255||0, 255, 255|
|Gray||170, 170, 170||192, 192, 192||203, 204, 205||187, 187, 187||229, 229, 229||255, 255, 255||255, 255, 255|
|Bright/light||Darkgray||85, 85, 85||128, 128, 128||129, 131, 131||85, 85, 85||127, 127, 127|
|Red||255, 85, 85||255, 0, 0||252,57,31||255, 85, 85||255, 0, 0|
|Green||85, 255, 85||0, 255, 0||49, 231, 34||85, 255, 85||0, 255, 0||144, 238, 144||144, 238, 144|
|Yellow||255, 255, 85||255, 255, 0||234, 236, 35||255, 255, 85||255, 255, 0||255, 255, 224||225, 255, 224|
|Blue||85, 85, 255||0, 0, 255||88, 51, 255||85, 85, 255||92, 92, 255||173, 216, 230||173, 216, 230|
|Magenta||255, 85, 255||255, 0, 255||249, 53, 248||255, 85, 255||255, 0, 255|
|Cyan||85, 255, 255||0, 255, 255||20, 240, 240||85, 255, 255||0, 255, 255||224, 255, 255||224, 255, 255|
|White||255, 255, 255||255, 255, 255||233, 235, 235||255, 255, 255||255, 255, 255|
The VGA column denotes the typical colors that are used when booting PCs and leaving them in their classical 80×25 text mode. The colors are different in the EGA/VGA graphic modes.
In July 2004, the blue colors of xterm changed, RGB (0,0,205) → (0,0,238) for normal and (0,0,255) → (92,92,255) for bright. As of 2010, old xterm versions still linger on many computers though.
Recent-enough versions of KDE's Konsole program support 24-bit foreground and background color setting[better source needed] Quoting one of the text-files in its source-tree:[better source needed]
ESC[ … 38;2;<r>;<g>;<b> … m Select RGB foreground color
ESC[ … 48;2;<r>;<g>;<b> … m Select RGB background color
In 256 color mode (ESC[38;5;<fgcode>m and ESC[48;5;<bgcode>m), the color-codes are the following:
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=216 colors: 16 + 36*r + 6*g + b (0≤r,g,b≤5) 0xe8-0xff: grayscale from black to white in 24 steps
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 re-assigns 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.
Users can employ escape codes in their scripts by including them as part of standard output or standard error. For example, the following sed command embellishes the output of the make command by displaying lines containing words starting with "ERR" in reverse video, and words starting with "WARN" in bold (letter case is ignored).
make 2>&1 | sed -e 's/.*\bERR.*/\x1b[7m&\x1b[0m/i' -e 's/.*\bWARN.*/\x1b[1m&\x1b[0m/i'
The representations of the codes are highlighted.
Invalid and ambiguous sequences in use
- The Linux console uses
OSC P n rr gg bbto change the palette, which, if hard-coded into an application, may hang other terminals. However, appending
STwill 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 generates
SS3 1; modifiers charwhen F1–F4 are pressed with modifiers. The faulty behavior was copied from GNOME Terminal.
- xterm replies
CSI row ; column Rif asked for cursor position and
CSI 1 ; modifiers Rif 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.[clarification needed]
- many terminals prepend
ESCto any character that is typed with the alt key down. This creates ambiguity for uppercase letters and symbols @[\]^_, which would form C1 codes.[clarification needed]
- Konsole generates
SS3 modifiers charwhen F1–F4 are pressed with modifiers.[clarification needed]
- See this NIST list of withdrawn standards
- Paul Williams (2006). "Digital's Video Terminals". VT100.net. Retrieved 17 August 2011.
- Heathkit Company (1979). "Heathkit Catalog 1979". Heathkit Company. Retrieved 4 November 2011.
- The screen display could be replaced by drawing the entire new screen's contents at the bottom, scrolling the previous screen up sufficiently to erase all the old text. The user would see the scrolling, and the hardware cursor would be left at the very bottom. Some early batch files achieved rudimentary "full screen" displays in this way.
- Michael Mefford (7 February 1989). "ANSI.com: Download It Here". PC Magazine. Retrieved 10 August 2011.
- Dan Kegel, Eric Auer (28 February 1999). "Nansi and NNansi - ANSI Drivers for MS-DOS". Dan Kegel's Web Hostel. Retrieved 10 August 2011.
- Jason Hood (2005). "Process ANSI escape sequences for Windows console programs". Jason Hood's Home page. Retrieved 9 May 2013.
- "Console Reference (Windows)". Microsoft. Retrieved 17 August 2013.
- "colorama 0.2.5 :". Python Package Index. Retrieved 17 August 2013.
- The names are standard, however the exact shade/hue/value of colors are not standardized and will depend on the device used to display them.
- On terminals based on CGA compatible hardware, such as ANSI.SYS running on DOS, this normal intensity foreground color is rendered as Orange. CGA RGBI monitors contained hardware to modify the dark yellow color to an orange/brown color by reducing the green component. See this ansi art as an example.
- "Patch #192 - 2004/7/12 - XFree86 220.127.116.11".
- "color-spaces.pl (a copy of 256colors2.pl from xterm dated 11 July 1999)". KDE. 6 December 2006.
- "README.moreColors". KDE. 22 April 2010.
- Colorized shell echo
- 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 February 6, 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