18.13. termcap, terminfo, and curses

termcap stands for "terminal capability," and it refers to the text file /etc/termcap and a set of routines to read this file. The termcap scheme was developed at Berkeley to support the vi editor. The termcap file contains descriptions of various terminals: what features the terminal supports (how many lines and rows, whether the terminal support backspace, etc.) and how to make the terminal perform certain operations (clear the screen, move the cursor to a given location, etc.). Taking this information out of the compiled program and placing it into a text file that can easily be edited allows the vi editor to run on many different terminals.

The routines that support the termcap file were then extracted from the vi editor and placed into a separate curses library. Many features were added to make this library usable for any program that wanted to manipulate the screen.

The termcap scheme was not perfect. As more and more terminals were added to the data file, it took longer to scan the file, looking for a specific terminal. The data file also used two-character names to identify the various terminal attributes. These deficiencies led to development of the terminfo scheme and its associated curses library. The terminal descriptions in terminfo are basically compiled versions of a textual description and can be located faster at runtime. terminfo appeared with SVR2 and has been in all System V releases since then.

Historically, System Vbased systems used terminfo, and BSD-derived systems used termcap, but it is now common for systems to provide both. Mac OS X, however, supports only terminfo.

A description of terminfo and the curses library is provided by Goodheart [1991], but this is currently out of print. Strang [1986] describes the Berkeley version of the curses library. Strang, Mui, and O'Reilly [1988] provide a description of termcap and terminfo.

The ncurses library, a free version that is compatible with the SVR4 curses interface, can be found at http://invisible-island.net/ncurses/ncurses.html.

Neither termcap nor terminfo, by itself, addresses the problems we've been looking at in this chapter: changing the terminal's mode, changing one of the terminal special characters, handling the window size, and so on. What they do provide is a way to perform typical operations (clear the screen, move the cursor) on a wide variety of terminals. On the other hand, curses does help with some of the details that we've addressed in this chapter. Functions are provided by curses to set raw mode, set cbreak mode, turn echo on and off, and the like. But the curses library is designed for character-based dumb terminals, which have mostly been replaced by pixel-based graphics terminals today.