ANSI escape code

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ANSI X3.64 (ISO/IEC 6429)
Htop.png
Output of the system-monitor htop, an ncurses-application (which uses SGR and other ANSI/ISO control sequences).
Standard
Classification ISO/IEC 2022 based control code and control sequence set
Other related encoding(s)

Other control function standards:

ANSI escape sequences are a standard for in-band signaling to control cursor location, color, font styling, and other options on video text terminals and terminal emulators. Certain sequences of bytes, most starting with an ASCII escape character and a bracket character, are embedded into text. The terminal interprets these sequences as commands, rather than text to display verbatim.

Contents

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 are used in development, scientific, commercial text-based applications as well as bulletin board systems to offer standardized functionality.

Although hardware text terminals have become increasingly rare in the 21st century, the relevance of the ANSI standard persists because a great majority of terminal emulators and command consoles interpret at least a portion of the ANSI standard.

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 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 DEC VT100 video display terminal. DEC VT100 terminal.jpg
The DEC VT100 video display terminal.

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. It is also adopted by ISO and IEC as standard ISO/IEC 6429. [5] A version is adopted as a Japanese Industrial Standard, as JIS X 0211.

Related standards include ITU T.61, the Teletex standard, and the ISO/IEC 8613, the Open Document Architecture standard (mainly ISO/IEC 8613-6 or ITU T.416). The two systems share many escape codes with the ANSI system, with extensions that are not necessarily meaningful to computer terminals. Both systems quickly fell into disuse, but ECMA-48 does mark the extensions used in them as reserved.

Platform support

The Xterm terminal emulator. XtermMenus.png
The Xterm terminal emulator.

In the early 1980s, large amounts of software directly used these sequences to update screen displays. This included everything on VMS (which assumed Dec terminals), most software designed to be portable on CP/M home computers, and even lots of Unix software as it was easier to use than the termcap libraries, such as the shell script examples below in this article.

Terminal emulators for communicating with remote machines almost always implement ANSI escape codes. This includes anything written to communicate with bulletin-board systems on home and personal computers. On Unix terminal emulators such as xterm also can communicate with software running on the same machine, and thus software running in X11 under a terminal emulator could assume the ability to write these sequences.

As computers got more powerful even built-in displays started supporting them, allowing software to be portable between CP/M systems. There were attempts to extend the escape sequences to support printers [6] and as an early PDF-like document storage format, the Open Document Architecture.[ citation needed ]

DOS and Windows

A huge blow to the popularity of the sequences was that the IBM PC, introduced in 1983, did not support them for local programs (this was common for "all in one" home computers, but rare for machines of this complexity). Only a few control characters (BEL, CR, LF, BS) were interpreted by the underlying BIOS, making it almost [lower-alpha 1] 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. This made any interesting software non-portable and led to the need to duplicate details of the display hardware in PC Clones.

DOS 2.0 introduced the ability to add a device driver for the ANSI escape sequences: ANSI.SYS . 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.[ citation 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.

Many clones of DOS were able to interpret the sequences and do not require a separate ANSI driver to be loaded. PTS-DOS [7] [8] as well as Concurrent DOS, Multiuser DOS [9] and REAL/32 have built-in support (plus a number of extensions). OS/2 had an ANSI command that enabled the sequences.

The Windows Console did not support ANSI escape sequences, nor did Microsoft provide any method to enable them. 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 [10] and Maximus5's ConEmu interpreted ANSI escape sequences printed by programs. A Python package named colorama [11] internally interprets ANSI escape sequences in text being printed, translating them to win32 calls to modify the state of the terminal, to make it easier to port Python code using ANSI to Windows. Cygwin performs similar translation to all output written to the console using Cygwin file descriptors, the filtering is done by the output functions of cygwin1.dll, to allow porting of POSIX C code to Windows.

In 2016, Microsoft released the Windows 10 version 1511 update which unexpectedly implemented support for ANSI escape sequences, over two decades after the debut of Windows NT. [12] This was done alongside Windows Subsystem for Linux, allowing Unix-like terminal-based software to use the sequences in Windows Console. This defaults to off, but Windows PowerShell 5.1 enabled it. PowerShell 6 made it possible to embed the necessary ESC character into a string with `e. [13]

Windows Terminal, introduced in 2019, supports the sequences by default, and Microsoft intends to replace the Windows Console with Windows Terminal. [14]

Description

C0 control codes

Almost all users assume some functions of some single-byte characters. Initially defined as part of ASCII, the default C0 control code set is now defined in ISO 6429 (ECMA-48), making it part of the same standard as the C1 set invoked by the ANSI escape sequences (although ISO 2022 allows the ISO 6429 C0 set to be used without the ISO 6429 C1 set, and vice versa, provided that 0x1B is always ESC). This is used to shorten the amount of data transmitted, or to perform some functions that are unavailable from escape sequences:

Popular C0 control codes (not an exhaustive list)
^ C0AbbrNameEffect
^G0x07BELBellMakes an audible noise.
^H0x08BSBackspaceMoves the cursor left (but may "backwards wrap" if cursor is at start of line).
^I0x09HTTabMoves the cursor right to next multiple of 8.
^J0x0ALFLine FeedMoves to next line, scrolls the display up if at bottom of the screen. Usually does not move horizontally, though programs should not rely on this.
^L0x0CFFForm FeedMove a printer to top of next page. Usually does not move horizontally, though programs should not rely on this. Effect on video terminals varies.
^M0x0DCRCarriage ReturnMoves the cursor to column zero.
^[0x1BESCEscapeStarts all the escape sequences

Escape sequences vary in length. The general format for an ANSI-compliant escape sequence is defined by ANSI X3.41 (equivalent to ECMA-35 or ISO/IEC 2022). [15] :13.1 The escape sequences consist only of bytes in the range 0x20—0x7F (all the non-control ASCII characters), and can be parsed without looking ahead. The behavior when a control character, a byte with the high bit set, or a byte that is not part of any valid sequence, is encountered before the end is undefined.

Fe Escape sequences

If the ESC is followed by a byte in the range 0x40 to 0x5F, the escape sequence is of type Fe. Its interpretation is delegated to the applicable C1 control code standard. [15] :13.2.1 Accordingly, all escape sequences corresponding to C1 control codes from ANSI X3.64 / ECMA-48 follow this format. [5] :5.3.a

The standard says that, in 8-bit environments, the control functions corresponding to type Fe escape sequences (those from the set of C1 control codes) can be represented as single bytes in the 0x80–0x9F range. [5] :5.3.b This is possible in character encodings conforming to the provisions for an 8-bit code made in ISO 2022, such as the ISO 8859 series. However, in character encodings used on modern devices such as UTF-8 or CP-1252, those codes are often used for other purposes, so only the 2-byte sequence is typically used. In the case of UTF-8, representing a C1 control code via the C1 Controls and Latin-1 Supplement block results in a different two-byte code (e.g. 0xC2,0x8E for U+008E), but no space is saved this way.

Some type Fe (C1 set element) ANSI escape sequences (not an exhaustive list)
CodeC1AbbrNameEffect
ESC N0x8ESS2Single Shift TwoSelect a single character from one of the alternative character sets. SS2 selects the G2 character set, and SS3 selects the G3 character set. [16] In a 7-bit environment, this is followed by one or more GL bytes (0x20–0x7F) specifying a character from that set. [15] :9.4 In an 8-bit environment, these may instead be GR bytes (0xA0–0xFF). [15] :8.4
ESC O0x8FSS3Single Shift Three
ESC P0x90DCSDevice Control StringTerminated by ST. [5] :5.6 Xterm's uses of this sequence include defining User-Defined Keys, and requesting or setting Termcap/Terminfo data. [16]
ESC [0x9BCSI Control Sequence Introducer Starts most of the useful sequences, terminated by a byte in the range 0x40 through 0x7E. [5] :5.4
ESC \0x9CSTString TerminatorTerminates strings in other controls. [5] :8.3.143
ESC ]0x9DOSC Operating System Command Starts a control string for the operating system to use, terminated by ST. [5] :8.3.89
ESC X0x98SOSStart of StringTakes an argument of a string of text, terminated by ST. [5] :5.6 The uses for these string control sequences are defined by the application [5] :8.3.2,8.3.128 or privacy discipline. [5] :8.3.94 These functions are rarely implemented and the arguments are ignored by xterm. [16] Some Kermit clients allow the server to automatically execute Kermit commands on the client by embedding them in APC sequences; this is a potential security risk if the server is untrusted. [17]
ESC ^0x9EPMPrivacy Message
ESC _0x9FAPCApplication Program Command

CSI (Control Sequence Introducer) sequences

For Control Sequence Introducer, or CSI, commands, the ESC [ (written as \e[ or \033[ in several programming languages) 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

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.[ citation needed ]

Some ANSI control sequences (not an exhaustive list)
CodeAbbrNameEffect
CSI n ACUUCursor UpMoves 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 BCUDCursor Down
CSI n CCUFCursor Forward
CSI n DCUBCursor Back
CSI n ECNLCursor Next LineMoves cursor to beginning of the line n (default 1) lines down. (not ANSI.SYS)
CSI n FCPLCursor Previous LineMoves cursor to beginning of the line n (default 1) lines up. (not ANSI.SYS)
CSI n GCHACursor Horizontal AbsoluteMoves the cursor to column n (default 1). (not ANSI.SYS)
CSI n ; m HCUPCursor PositionMoves 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 JEDErase in DisplayClears 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 KELErase in LineErases part of the line. If n is 0 (or missing), clear from cursor to the end of the line. If n is 1, clear from cursor to beginning of the line. If n is 2, clear entire line. Cursor position does not change.
CSI n SSUScroll UpScroll whole page up by n (default 1) lines. New lines are added at the bottom. (not ANSI.SYS)
CSI n TSDScroll DownScroll whole page down by n (default 1) lines. New lines are added at the top. (not ANSI.SYS)
CSI n ; m fHVPHorizontal Vertical PositionSame as CUP, but counts as a format effector function (like CR or LF) rather than an editor function (like CUD or CNL). This can lead to different handling in certain terminal modes. [5] :Annex A
CSI n mSGR Select Graphic Rendition Sets colors and style of the characters following this code
CSI 5iAUX Port OnEnable aux serial port usually for local serial printer
CSI 4iAUX Port OffDisable aux serial port usually for local serial printer

CSI 6nDSRDevice Status ReportReports the cursor position (CPR) by transmitting ESC[n;mR, where n is the row and m is the column.
Some popular private sequences
CodeAbbrNameEffect
CSI sSCP, SCOSCSave Current Cursor PositionSaves the cursor position/state in SCO console mode. [18] In vertical split screen mode, instead used to set (as CSI n ; n s) or reset left and right margins. [19]
CSI uRCP, SCORCRestore Saved Cursor PositionRestores the cursor position/state in SCO console mode. [20]
CSI ? 25 hDECTCEMShows the cursor, from the VT220.
CSI ? 25 lDECTCEMHides the cursor.
CSI ? 1004 hEnable reporting focus. Reports whenever terminal emulator enters or exits focus as ESC [I and ESC [O, respectively.
CSI ? 1004 lDisable reporting focus.
CSI ? 1049 hEnable alternative screen buffer, from xterm
CSI ? 1049 lDisable alternative screen buffer, from xterm
CSI ? 2004 hTurn on bracketed paste mode. [21] In bracketed paste mode, text pasted into the terminal will be surrounded by ESC [200~ and ESC [201~; programs running in the terminal should not treat characters bracketed by those sequences as commands (Vim, for example, does not treat them as commands). [22] From xterm [23]
CSI ? 2004 lTurn off bracketed paste mode.

SGR (Select Graphic Rendition) parameters

The control sequence CSI n m, named Select Graphic Rendition (SGR), sets display attributes. Several attributes can be set in the same sequence, separated by semicolons. [24] 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).

nNameNote
0Reset or normalAll attributes become turned off
1Bold or increased intensityAs with faint, the color change is a PC (SCO / CGA) invention. [25] [ better source needed ]
2Faint, decreased intensity, or dimMay be implemented as a light font weight like bold. [26]
3ItalicNot widely supported. Sometimes treated as inverse or blink. [25]
4UnderlineStyle extensions exist for Kitty, VTE, mintty, iTerm2 and Konsole. [27] [28] [29]
5Slow blinkSets blinking to less than 150 times per minute
6Rapid blinkMS-DOS ANSI.SYS, 150+ per minute; not widely supported
7 Reverse video or invertSwap foreground and background colors; inconsistent emulation [30] [ dubious ]
8Conceal or hideNot widely supported.
9 Crossed-out, or strikeCharacters legible but marked as if for deletion. Not supported in Terminal.app.
10Primary (default) font
11–19Alternative fontSelect alternative font n − 10
20 Fraktur (Gothic)Rarely supported
21Doubly underlined; or: not boldDouble-underline per ECMA-48, [5] :8.3.117 but instead disables bold intensity on several terminals, including in the Linux kernel's console before version 4.17. [31]
22Normal intensityNeither bold nor faint; color changes where intensity is implemented as such.
23Neither italic, nor blackletter
24Not underlinedNeither singly nor doubly underlined
25Not blinkingTurn blinking off
26Proportional spacing ITU T.61 and T.416, not known to be used on terminals
27Not reversed
28RevealNot concealed
29Not crossed out
30–37Set foreground color
38Set foreground color Next arguments are 5;n or 2;r;g;b
39Default foreground colorImplementation defined (according to standard)
40–47Set background color
48Set background color Next arguments are 5;n or 2;r;g;b
49Default background colorImplementation defined (according to standard)
50Disable proportional spacingT.61 and T.416
51FramedImplemented as "emoji variation selector" in mintty. [32]
52Encircled
53OverlinedNot supported in Terminal.app
54Neither framed nor encircled
55Not overlined
58Set underline color Not in standard; implemented in Kitty, VTE, mintty, and iTerm2. [27] [28] Next arguments are 5;n or 2;r;g;b.
59Default underline colorNot in standard; implemented in Kitty, VTE, mintty, and iTerm2. [27] [28]
60Ideogram underline or right side lineRarely supported
61Ideogram double underline, or double line on the right side
62Ideogram overline or left side line
63Ideogram double overline, or double line on the left side
64Ideogram stress marking
65No ideogram attributesReset the effects of all of 6064
73SuperscriptImplemented only in mintty [32]
74Subscript
75Neither superscript nor subscript
90–97Set bright foreground colorNot in standard; originally implemented by aixterm [16]
100–107Set bright background color

Colors

3-bit and 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.

The chart below shows a few examples of how VGA standard and modern terminal emulators translate the 4-bit color codes into 24-bit color codes.

FGBGNameVGA [lower-alpha 2] Windows XP
Console
[lower-alpha 3]
Windows
PowerShell&
1.0–6.0
[lower-alpha 4]
Visual Studio Code [lower-alpha 5] Windows 10
Console
[lower-alpha 6]
Terminal.app PuTTY mIRC xterm Ubuntu [lower-alpha 7] Eclipse Terminal
3040Black0,0,012,12,120,0,01,1,10,0,0
3141Red170,0,0128,0,0205, 49, 49197,15,31153,0,0187,0,0127,0,0205,0,0222,56,43205,0,0
3242Green0,170,00,128,013, 188, 12119,161,140,166,00,187,00,147,00,205,057,181,740,205,0
3343Yellow170,85,0 [lower-alpha 8] 128,128,0238,237,240229, 229, 16193,156,0153,153,0187,187,0252,127,0205,205,0255,199,6205,205,0
3444Blue0,0,1700,0,12836, 114, 2000,55,2180,0,1780,0,1870,0,1270,0,238 [34] 0,111,1840,0,238
3545Magenta170,0,170128,0,1281,36,86188, 63, 188136,23,152178,0,178187,0,187156,0,156205,0,205118,38,113205,0,205
3646Cyan0,170,1700,128,12817, 168, 20558,150,2210,166,1780,187,1870,147,1470,205,20544,181,2330,205,205
3747White170,170,170192,192,192229, 229, 229204,204,204191,191,191187,187,187210,210,210229,229,229204,204,204229,229,229
90100Bright Black (Gray)85,85,85128,128,128102, 102, 102118,118,118102,102,10285,85,85127,127,127127,127,127128,128,1280,0,0
91101Bright Red255,85,85255,0,0241, 76, 76231,72,86230,0,0255,85,85255,0,0
92102Bright Green85,255,850,255,035, 209, 13922,198,120,217,085,255,850,252,00,255,0
93103Bright Yellow255,255,85255,255,0245, 245, 67249,241,165230,230,0255,255,85255,255,0
94104Bright Blue85,85,2550,0,25559, 142, 23459,120,2550,0,25585,85,2550,0,25292,92,255 [35] 0,0,25592,92,255
95105Bright Magenta255,85,255255,0,255214, 112, 214180,0,158230,0,230255,85,255255,0,255
96106Bright Cyan85,255,2550,255,25541, 184, 21997,214,2140,230,23085,255,2550,255,255
97107Bright White255,255,255229, 229, 229242,242,242230,230,230255,255,255
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:[ citation needed ]

ESC[38;5;nm Select foreground color      where n is a number from the table below ESC[48;5;nm Select background color   0-  7:  standard colors (as in ESC [ 30–37 m)   8- 15:  high intensity colors (as in ESC [ 90–97 m)  16-231:  6 × 6 × 6 cube (216 colors): 16 + 36 × r + 6 × g + b (0 ≤ r, g, b ≤ 5) 232-255:  grayscale from dark to light in 24 steps

The ITU's T.416 Information technology - Open Document Architecture (ODA) and interchange format: Character content architectures [36] uses ":" as separator characters instead:

ESC[38:5:nm Select foreground color      where n is a number from the table below ESC[48:5:nm Select background color

256-color mode — foreground: ESC[38;5;#m   background: ESC[48;5;#m
Standard colorsHigh-intensity colors
 0  1  2  3  4  5  6  7  8  9 101112131415
216 colors
161718192021222324252627282930313233343536373839404142434445464748495051
525354555657585960616263646566676869707172737475767778798081828384858687
888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123
124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159
160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195
196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231
Grayscale colors
232233234235236237238239240241242243244245246247248249250251252253254255

There has also been a similar but incompatible 88-color encoding using the same escape sequence, seen in rxvt and xterm-88color. Not much is known about the scheme besides the color codes. It uses a 4×4×4 color cube.

24-bit

As "true color" graphic cards with 16 to 24 bits of color became common, applications began to support 24-bit colors. Terminal emulators supporting setting 24-bit foreground and background colors with escape sequences include Xterm, [16] KDE's Konsole, [37] [38] and iTerm, as well as all libvte based terminals, [39] including GNOME Terminal. [40]

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

The syntax is likely based on the ITU's T.416 Open Document Architecture (ODA) and interchange format: Character content architectures, [36] which was adopted as ISO/IEC 8613-6 but ended up as a commercial failure.[ citation needed ] The ODA version is more elaborate and thus incompatible:

  • The parameters after the '2' (r, g, and b) are optional and can be left empty.
  • Semicolons are replaced by colons, as above.
  • There is a leading "colorspace ID". [16] The definition of the colorspace ID is not included in that document so it may be blank to represent the unspecified default.
  • In addition to the '2' value after 48 to specify a Red-Green-Blue format (and the '5' above for a 0-255 indexed color), there are alternatives of '0' for implementation-defined and '1' for transparent - neither of which have any further parameters; '3' specifies colors using a Cyan-Magenta-Yellow scheme, and '4' for a Cyan-Magenta-Yellow-Black one, the latter using the position marked as "unused" for the Black component: [36]
ESC[38:2:Color-Space-ID:r:g:b:unused: CS tolerance :Color-Space associated with tolerance: 0 for "CIELUV"; 1 for "CIELAB" m Select RGB foreground color ESC[48:2:Color-Space-ID:r:g:b:unused:CS tolerance:Color-Space associated with tolerance: 0 for "CIELUV"; 1 for "CIELAB" m Select RGB background color

The ITU-RGB variation is supported by xterm, with the colorspace ID and tolerance parameters ignored. The simpler scheme using semicolons is initially found in Konsole. [16] :Can I set a color by its number?

Unix environment variables relating to color support

Rather than using the color support in termcap and terminfo introduced in SVr3.2 (1987), [41] the S-Lang library (version 0.99-32, June 1996) used a separate environment variable $COLORTERM to indicate whether a terminal emulator could use colors at all, and later added values to indicate if it supported 24-bit color. [42] [43] This system, although poorly documented, became widespread enough for Fedora and RHEL to consider using it as a simpler and more universal detection mechanism compared to querying the now-updated libraries. [44]

Some terminal emulators (urxvt, konsole) set $COLORFGBG to report the color scheme of the terminal (mainly light vs. dark background). This behavior originated in S-Lang [43] and is used by vim. Gnome-terminal refuses to add this behavior, as the syntax for the value is not agreed upon, the value cannot be changed upon a runtime change of the palette, and more "proper" xterm OSC 4/10/11 sequences already exist. [45]

OSC (Operating System Command) sequences

Most Operating System Command sequences were defined by Xterm, but many are also supported by other terminal emulators. For historical reasons, Xterm can end the command with BEL (0x07) as well as the standard ST (0x9C or 0x1B 0x5C). [16] For example, Xterm allows the window title to be set by ESC ]0;this is the window title BEL.

A non-xterm extension is the hyperlink, ESC ]8;;link ST from 2017, used by VTE, [46] [ discuss ] iTerm2, [46] and mintty, [47] among others. [48]

The Linux console uses ESC ] P n rr gg bb to change the palette, which, if hard-coded into an application, may hang other terminals. [49] However, appending ST will be ignored by Linux and form a proper, ignorable sequence for other terminals.[ citation needed ]

Fs Escape sequences

If the ESC is followed by a byte in the range 0x60—0x7E, the escape sequence is of type Fs. This type is used for control functions individually registered with the ISO-IR registry. [50] A table of these is listed under ISO/IEC 2022.

Fp Escape sequences

If the ESC is followed by a byte in the range 0x30—0x3F, the escape sequence is of type Fp, which is set apart for up to sixteen private-use control functions. [15] :6.5.3

Some type Fp (private-use) escape sequences recognised by the VT100
AbbrNameEffect
ESC 7DECSCDEC Save CursorSaves the cursor position, encoding shift state and formatting attributes. [51] [16]
ESC 8DECRCDEC Restore CursorRestores the cursor position, encoding shift state and formatting attributes from the previous DECSC if any, otherwise resets these all to their defaults. [51] [16]

nF Escape sequences

If the ESC is followed by a byte in the range 0x20—0x2F, the escape sequence is of type nF. Said byte is followed by any number of additional bytes in this range, and then a byte in the range 0x30-0x7E. These escape sequences are further subcategorised by the low two bits of the first byte, e.g. "type 2F" for sequences where the first byte is 0x22; and by whether the final byte is in the range 0x30—0x3F indicating private use (e.g. "type 2Fp") or not (e.g. "type 2Ft"). [15] :13.2.1

Most of the nFt sequences are for changing the current character set, and are listed in ISO/IEC 2022. Some others:

Some type 0Ft (announcement) ANSI escape sequences [16] [15] :15.2
AbbrNameEffect
ESC SP F
  • ACS6
  • S7C1T
  • Announce Code Structure 6
  • Send 7-bit C1 Control Character to the Host
Makes the function keys send ESC + letter instead of 8-bit C1 codes.
ESC SP G
  • ACS7
  • S8C1T
  • Announce Code Structure 7
  • Send 8-bit C1 Control Character to the Host
Makes the function keys send 8-bit C1 codes.

If the first byte is '#' the public sequences are reserved for additional ISO-IR registered individual control functions. [15] :6.5.2 No such sequences are presently registered. [50] Type 3Fp sequences (which includes ones starting with '#') are available for private-use control functions. [15] :6.5.3

Some type 3Fp (private-use) escape sequences recognised by the VT100
AbbrNameEffect
ESC # 3DECDHLDEC Double-Height Letters, Top HalfMakes the current line use characters twice as tall. This code is for the top half. [52]
ESC # 4DECDHLDEC Double-Height Letters, Bottom HalfMakes the current line use characters twice as tall. This code is for the bottom half. [52]
ESC # 5DECSWLDEC Single-Width LineMakes the current line use single-width characters, per the default behaviour. [53] [16]
ESC # 6DECDWLDEC Double-Width LineMakes the current line use double-width characters, discarding any characters in the second half of the line. [54] [16]

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. 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.

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. [55]

make 2>&1 | sed -e 's/.*\bWARN.*/\x1b[7m&\x1b[0m/i' -e 's/.*\bERR.*/\x1b[93;41m&\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. [56]

flasher(){whiletrue;doprintf\\e[?5h;sleep0.1;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. [57]

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.

In C

Output of example program on Gnome Terminal ANSI sample program output.png
Output of example program on Gnome Terminal
#include<stdio.h>intmain(void){inti,j,n;for(i=0;i<11;i++){for(j=0;j<10;j++){n=10*i+j;if(n>108)break;printf("\033[%dm %3d\033[m",n,n);}printf("\n");}return0;}

Terminal input sequences

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.

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. To complicate the matter, the VT terminals themselves have two schemes of input, normal mode and application mode that can be switched by the application.

(draft section)

<char>                                         -> char <esc> <nochar>                                 -> esc <esc> <esc>                                    -> esc <esc> <char>                                   -> Alt-keypress or keycode sequence <esc> '[' <nochar>                             -> Alt-[ <esc> '[' (<modifier>) <char>                  -> keycode sequence, <modifier> is a decimal number and defaults to 1 (xterm) <esc> '[' (<keycode>) (';'<modifier>) '~'      -> keycode sequence, <keycode> and <modifier> are decimal numbers and default to 1 (vt) 

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 F9, <esc>[5C is Ctrl+.

In other words, the modifier is the sum of the following numbers:

Key pressedNumberComment
1always added, the rest are optional
Shift1
(Left) Alt2
Control4
Meta8
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 <modifier> is normally omitted if no modifier keys are pressed, but most implementations always emit the <modifier> for F1F4. (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. [16] Thomas Dickey has added a lot of support to it over time; [58] he also maintains a list of default keys used by other terminal emulators for comparison. [59]

See also

Notes

  1. 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.
  2. Typical colors that are used when booting PCs and leaving them in text mode, which used a 16-entry color table. The colors are different in the EGA/VGA graphic modes.
  3. Seen in Windows XP through Windows 8.1
  4. PowerShell's default shortcut .lnk, unchanged for over a decade, remaps yellow and magenta to give PowerShell distinctive foreground/background colors compared to the Command Prompt. [33] PowerShell 7 is unaffected.
  5. Debug console, "Dark+" theme
  6. Campbell theme, used as of Windows 10 version 1709.
  7. For virtual terminals, from /etc/vtrgb.
  8. 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 Archived 25 July 2011 at the Wayback Machine as an example.

Related Research Articles

<span class="mw-page-title-main">ASCII</span> American character encoding standard

ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of technical limitations of computer systems at the time it was invented, ASCII has just 128 code points, of which only 95 are printable characters, which severely limited its scope. Modern computer systems have evolved to use Unicode, which has millions of code points, but the first 128 of these are the same as the ASCII set.

<span class="mw-page-title-main">ISO/IEC 8859-1</span> Character encoding

ISO/IEC 8859-1:1998, Information technology — 8-bit single-byte coded graphic character sets — Part 1: Latin alphabet No. 1, is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1987. ISO/IEC 8859-1 encodes what it refers to as "Latin alphabet no. 1", consisting of 191 characters from the Latin script. This character-encoding scheme is used throughout the Americas, Western Europe, Oceania, and much of Africa. It is the basis for some popular 8-bit character sets and the first two blocks of characters in Unicode.

<span class="mw-page-title-main">Terminal emulator</span> Program that emulates a video terminal

A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.

<span class="mw-page-title-main">VT100</span> Computer terminal from Digital Equipment Corporation

The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special features like controlling the status lights on the keyboard. This led to rapid uptake of the ANSI standard, which became the de facto standard for hardware video terminals and later terminal emulators.

In computer science, an escape sequence is a combination of characters that has a meaning other than the literal characters contained therein; it is marked by one or more preceding characters.

<span class="mw-page-title-main">Newline</span> Special characters in computing signifying the end of a line of text

A newline is a control character or sequence of control characters in character encoding specifications such as ASCII, EBCDIC, Unicode, etc. This character, or a sequence of characters, is used to signify the end of a line of text and the start of a new one.

<span class="mw-page-title-main">Computer terminal</span> Computer input/output device for users

A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and predated the use of a computer screen by decades. Starting in the mid-1970s with machines such as the Sphere 1, Sol-20, and Apple I, terminal circuitry began to be integrated into personal and workstation computer systems, with the computer handling character generation and outputting to a CRT display such as a computer monitor or, sometimes, a consumer TV.

<span class="mw-page-title-main">VT220</span> Computer terminal from Digital Equipment Corporation

The VT220 is a computer terminal introduced by Digital Equipment Corporation (DEC) in November 1983. The VT240 added monochrome ReGIS vector graphics support to the base model, while the VT241 did the same in color. The 200 series replaced the successful VT100 series, providing more functionality in a much smaller unit with a much smaller and lighter keyboard. Like the VT100, the VT200 series implemented a large subset of ANSI X.364. Among its major upgrades was a number of international character sets, as well as the ability to define new character sets.

The null character is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646, the C0 control code, the Universal Coded Character Set, and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL. In 8-bit codes, it is known as a null byte.

ISO/IEC 2022Information technology—Character code structure and extension techniques, is an ISO/IEC standard in the field of character encoding. It is equivalent to the ECMA standard ECMA-35, the ANSI standard ANSI X3.41 and the Japanese Industrial Standard JIS X 0202. Originating in 1971, it was most recently revised in 1994.

<span class="mw-page-title-main">Text-based user interface</span> Type of interface based on outputting to or controlling a text display

In computing, text-based user interfaces (TUI), is a retronym describing a type of user interface (UI) common as an early form of human–computer interaction, before the advent of bitmapped displays and modern conventional graphical user interfaces (GUIs). Like modern GUIs, they can use the entire screen area and may accept mouse and other inputs. They may also use color and often structure the display using box-drawing characters such as ┌ and ╣. The modern context of use is usually a terminal emulator.

Text mode is a computer display mode in which content is internally represented on a computer screen in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of character cells, each of which contains one of the characters of a character set; at the same time, contrasted to graphics mode or other kinds of computer graphics modes.

<span class="mw-page-title-main">Shift Out and Shift In characters</span> ASCII control characters

Shift Out (SO) and Shift In (SI) are ASCII control characters 14 and 15, respectively. These are sometimes also called "Control-N" and "Control-O".

ANSI.SYS is a device driver in the DOS family of operating systems that provides extra console functions through ANSI escape sequences. It is partially based upon a subset of the text terminal control standard proposed by the ANSI X3L2 Technical Committee on Codes and Character Sets.

xterm Standard terminal emulator for the X Window system

xterm is the standard terminal emulator for the X Window System. It allows users to run programs which require a command-line interface.

<span class="mw-page-title-main">Esc key</span> Computer key

On computer keyboards, the Esc keyEsc is a key used to generate the escape character. The escape character, when sent from the keyboard to a computer, often is interpreted by software as "stop", "cancel" or "exit", and when sent from the computer to an external device marks the beginning of an escape sequence to specify operating modes or characteristics generally.

<span class="mw-page-title-main">GNOME Terminal</span> Terminal emulator from GNOME

GNOME Terminal is a terminal emulator for the GNOME desktop environment written by Havoc Pennington and others. Terminal emulators allow users to access a UNIX shell while remaining on their graphical desktop.

The C0 and C1 control code or control character sets define control codes for use in text by computer systems that use ASCII and derivatives of ASCII. The codes represent additional information about the text, such as the position of a cursor, an instruction to start a new line, or a message that the text has been received.

luit

luit is a utility program used to translate the character set of a computer program so that its output can be displayed correctly on a terminal emulator that uses a different character set. Whereas iconv converts the character set of strings or text files at rest, luit converts the input and output of programs running interactively.

Bracketed paste, is a mode of some terminal emulators which allows programs running in the terminal to treat pasted text differently from text typed normally.

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