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The Termcap Library

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3.1 Basic Characteristics

This section documents the capabilities that describe the basic and nature of the terminal, and also those that are relevant to the output of graphic characters.

Flag whose presence means that the terminal can overstrike. This means that outputting a graphic character does not erase whatever was present in the same character position before. The terminals that can overstrike include printing terminals, storage tubes (all obsolete nowadays), and many bit-map displays.

Flag whose presence means that outputting a space erases a character position even if the terminal supports overstriking. If this flag is not present and overstriking is supported, output of a space has no effect except to move the cursor.

(On terminals that do not support overstriking, you can always assume that outputting a space at a position erases whatever character was previously displayed there.)

Flag whose presence means that this terminal type is a generic type which does not really describe any particular terminal. Generic types are intended for use as the default type assigned when the user connects to the system, with the intention that the user should specify what type he really has. One example of a generic type is the type `network'.

Since the generic type cannot say how to do anything interesting with the terminal, termcap-using programs will always find that the terminal is too weak to be supported if the user has failed to specify a real terminal type in place of the generic one. The `gn' flag directs these programs to use a different error message: "You have not specified your real terminal type", rather than "Your terminal is not powerful enough to be used".

Flag whose presence means this is a hardcopy terminal.

String of commands to output a graphic character c, repeated n times. The first parameter value is the ASCII code for the desired character, and the second parameter is the number of times to repeat the character. Often this command requires padding proportional to the number of times the character is repeated. This effect can be had by using parameter arithmetic with `%'-sequences to compute the amount of padding, then generating the result as a number at the front of the string so that tputs will treat it as padding.

Flag whose presence means that the ASCII character `~' cannot be output on this terminal because it is used for display commands.

Programs handle this flag by checking all text to be output and replacing each `~' with some other character(s). If this is not done, the screen will be thoroughly garbled.

The old Hazeltine terminals that required such treatment are probably very rare today, so you might as well not bother to support this flag.

String whose presence means the terminal has a settable command character. The value of the string is the default command character (which is usually ESC).

All the strings of commands in the terminal description should be written to use the default command character. If you are writing an application program that changes the command character, use the `CC' capability to figure out how to translate all the display commands to work with the new command character.

Most programs have no reason to look at the `CC' capability.

Flag whose presence identifies Superbee terminals which are unable to transmit the characters ESC and Control-C. Programs which support this flag are supposed to check the input for the code sequences sent by the F1 and F2 keys, and pretend that ESC or Control-C (respectively) had been read. But this flag is obsolete, and not worth supporting.

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