Terminal capabilities

In computing and telecommunications, the capabilities of a terminal are various terminal features, above and beyond what is available from a pure teletypewriter, that host systems (and the programs that run on them) can make use of. They are (mainly) of control codes and escape codes that can be sent to or received from the terminal. The escape codes sent to the terminal perform various functions that a CRT terminal (and software terminal emulators) is capable of, but that a teletypewriter is not; such as moving the terminal's cursor to positions on the screen, clearing and scrolling all or parts of the screen, turning on and off attached printer devices, programming programmable function keys, changing display colours and attributes (such as reverse video), and setting display title strings. The escape codes received from the terminal signify things such as function key, arrow key, and other special key (home key, end key, help key, PgUp key, PgDn key, insert key, delete key, and so forth) keystrokes.

In Unix and other POSIX-compliant systems that support the POSIX terminal interface, these capabilities are encoded in databases that are configured by a system administrator and accessed from programs via the terminfo library (which supersedes the older termcap library), upon which in turn are built libraries such as the curses and ncurses libraries, by which applications programs use the terminal capabilities to provide textual user interfaces with windows, dialogue boxes, buttons, labels, input fields, menus, and so forth. The intention is that this allows applications programs to be independent of actual terminal characteristics. They don't need to hardwire any control codes or escape sequences into their code, and so don't have problems being used on a range of terminals with a range of capabilities.

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