ANSI escape code

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). The Hazeltine 1500 had a similar feature, invoked using ~, DC1 and then the X and Y positions separated with a comma. While the two terminals had identical functionality in this regard, different control sequences had to be used to invoke them.

As these sequences were different for different terminals, elaborate libraries such as termcap ("terminal capabilities") 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 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.[1] 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.[1] 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.[2] 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.[3] 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 and other online services) 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.[4]

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

Sequences have different lengths. All sequences start with ESC (27 / hex 0x1B / oct 033), followed by a second byte in the range 0x40–0x5F (ASCII @A–Z[\]^_).[5]^:5.3.a

The standard says that in 8-bit environments these two-byte sequences can be merged into single C1 control code in the 0x80–0x9F range.[5]^:5.3.b 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 typically used.

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

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.

For CSI, or "Control Sequence Introducer" commands, 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{|}~).[5]^:5.4

All common sequences just use the parameters as a series of semicolon-separated numbers such as 1;2;3. Missing numbers are treated as 0 (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 missing parameters useful.[5]^:F.4.2 Bytes other than digits and semicolon 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. Sequences containing the parameter bytes <=>? or the final bytes 0x70–0x7E (p–z{|}~) are private.

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.

SGR (Select Graphic Rendition) sets display attributes. Several attributes can be set in the same sequence, separated by semicolons.[25] Each display attribute remains in effect until a following occurrence of SGR resets it.[5] If no codes are given, CSI m is treated as CSI 0 m (reset / normal).

In ECMA-48 SGR is called "Select Graphic Rendition".[5]^:8.3.117 In Linux manual pages the term "Set Graphics Rendition" is used.[25]

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. The green may be a 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. Some implementations use the Bold state to make the character Bright.

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.

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

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

printf \\033c

Example of use in C

Output of example program on Gnome Terminal

 1 #include <stdio.h>
 2 
 3 int main(void)
 4 {
 5   int i, j, n;
 6   
 7   for (i = 0; i < 11; i++) {
 8     for (j = 0; j < 10; j++) {
 9       n = 10*i + j;
10       if (n > 108) break;
11       printf("\033[%dm %3d\033[m", n, n);
12     }
13     printf("\n");
14   }
15   return (0);
16 }

When typing input on a terminal keypresses outside the normal main alphanumeric keyboard area can be sent to the host as ANSI sequences. For keys that have an equivalent output function, such as the cursor keys, these often mirror the output sequences. However, for most keypresses there isn't an equivalent output sequence to use.

There are several encoding schemes, and unfortunately most terminals mix sequences from different schemes, so host software has to be able to deal with input sequences using any scheme.

(draft section)

<char>                                -> char
<esc> <nochar>                        -> esc
<esc> <esc>                           -> esc
<esc> <char>                          -> Alt-keypress or keycode sequence
<esc> '[' <nochar>                    -> Alt-[
<esc> '[' (<num>) (';'<num>) '~'      -> keycode sequence, <num> defaults to 1

If the terminating character is '~', the first number must be present and is a keycode number, the second number is an optional modifier value. If the terminating character is a letter, the letter is the keycode value, and the optional number is the modifier value.

The modifier value defaults to 1, and after subtracting 1 is a bitmap of modifier keys being pressed: Meta-Ctrl-Alt-Shift. So, for example, <esc>[4;2~ is Shift-End, <esc>[20~ is function key 9, <esc>[5C is Ctrl-Right.

vt sequences:
<esc>[1~    - Home        <esc>[16~   -             <esc>[31~   - F17
<esc>[2~    - Insert      <esc>[17~   - F6          <esc>[32~   - F18
<esc>[3~    - Delete      <esc>[18~   - F7          <esc>[33~   - F19
<esc>[4~    - End         <esc>[19~   - F8          <esc>[34~   - F20
<esc>[5~    - PgUp        <esc>[20~   - F9          <esc>[35~   - 
<esc>[6~    - PgDn        <esc>[21~   - F10         
<esc>[7~    - Home        <esc>[22~   -             
<esc>[8~    - End         <esc>[23~   - F11         
<esc>[9~    -             <esc>[24~   - F12         
<esc>[10~   - F0          <esc>[25~   - F13         
<esc>[11~   - F1          <esc>[26~   - F14         
<esc>[12~   - F2          <esc>[27~   -             
<esc>[13~   - F3          <esc>[28~   - F15         
<esc>[14~   - F4          <esc>[29~   - F16         
<esc>[15~   - F5          <esc>[30~   -             

xterm sequences:
<esc>[A     - Up          <esc>[K     -             <esc>[U     -
<esc>[B     - Down        <esc>[L     -             <esc>[V     -
<esc>[C     - Right       <esc>[M     -             <esc>[W     -
<esc>[D     - Left        <esc>[N     -             <esc>[X     -
<esc>[E     -             <esc>[O     -             <esc>[Y     -
<esc>[F     - End         <esc>[1P    - F1          <esc>[Z     -
<esc>[G     - Keypad 5    <esc>[1Q    - F2       
<esc>[H     - Home        <esc>[1R    - F3       
<esc>[I     -             <esc>[1S    - F4       
<esc>[J     -             <esc>[T     - 

<esc>[A to <esc>[D are the same as the ANSI output sequences. The <num> is normally omitted if no modifier keys are pressed, but most implementations always emit the <num> for F1-F4. (draft section)

Xterm has a comprehensive documentation page on the various function-key and mouse input sequence schemes from DEC's VT terminals and various other terminals it emulates.[19] Thomas Dickey has added a lot of support to it over time;[35] he also maintains a list of default keys used by other terminal emulators for comparison.[36]

• ANSI art
• Control character
• Advanced Video Attribute Terminal Assembler and Recreator (AVATAR)
• ISO/IEC JTC 1/SC 2
• C0 and C1 control codes

• 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". Archived from the original on 6 February 2006. Retrieved 22 February 2007.
• 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