ANSI escape code

In computing, ANSI escape codes (or escape sequences) are a method using in-band signaling to control the formatting, color, and other output options on video text terminals. To encode this formatting information, certain sequences of bytes are embedded into the text, which the terminal looks for and interprets as commands, not as character codes.

ANSI codes were introduced in the 1970s and became widespread in the minicomputer/mainframe market by the early 1980s. They were used by the nascent bulletin board system market to offer improved displays compared to earlier systems lacking cursor movement, leading to even more widespread use.

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 the output text. One notable exception was the Win32 console component of Microsoft Windows before Windows 10 update TH2.

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 platforms, elaborate libraries such as termcap had to be created so programs could use the same API to work with any terminal. Most of these systems 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.

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