ANSI escape code

ANSI escape sequences are a standard for in-band signaling to control the cursor location, color, and other options on video text terminals and terminal emulators. 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 in development, scientific and commercial applications and later by the nascent bulletin board systems to offer improved displays compared to earlier systems lacking cursor movement, a primary reason 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. A notable exception was DOS and older versions of the Win32 console of Microsoft Windows. 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 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.