Termcap (terminal capability) is a software library and
databaseused on Unix-likecomputers. It enables programs to use display computer terminals in a device-independent manner, which greatly simplifies the process of writing portable text modeapplications. Bill Joywrote the first termcap library [ [http://www.byte.com/art/9410/sec8/art3.htm Peter H. Salus, "The history of Unix is as much about collaboration as it is about technology", Byte, October 1994.] ] [ [http://www.mirbsd.org/cman/manPSD/19.curses.htm Kenneth C. R. C. Arnold and Elan Amir, "Screen Updating and Cursor Movement Optimization: A Library Package"] ] for the Berkeley Unix operating system; it has since been ported to most Unix and Unix-like environments. Joy's design was reportedly influenced by the design of the terminal data store in the earlier Incompatible Timesharing Systemsystem. [ [http://www.inwap.com/pdp10/usenet/its alt.sys.pdp10 posting] ]
A termcap database can describe the capabilities of hundreds of different display terminals.This allows external programs to be able to have character-based display output, independent of the type of terminal. On-screen text editors such as
viand emacsare examples of programs that may use termcap. Other programs are listed in the category.
Examples of what the database describes:
*how many columns wide it is
*what string to send to move the cursor to an arbitrary position (including how to encode the row and column numbers)
*how to scroll the screen up one or several lines
*how much padding is needed for such a scrolling operation.
Termcap databases consist of one or more descriptions of terminals.
Each description must contain the
canonicalname of the terminal.It may also contain one or more aliases for the name of the terminal.The canonical name or aliases are the keys by which the library searches the termcap database.
The description contains one or more capabilities, which have conventional names.The capabilities are typed: "boolean", "numeric" and "string".The termcap library has no predetermined type for each capability name.It determines the types of each capability by the syntax:
* "string" capabilities have an "=" between the capability name and its value,
* "numeric" capabilities have a "#" between the capability name and its value, and
* "boolean" capabilities have no associated value (they are always "true" if specified).
Applications which use termcap do expect specific types for the commonly used capabilities,and obtain the values of capabilities from the termcap database using library calls that return successfullyonly when the database contents matches the assumed type.
Termcap descriptions can be constructed by including the contents of one description in another,suppressing capabilities from the included description or overriding or adding capabilities.No matter what
storage modelis used, the termcap library constructs the terminal descriptionfrom the requested description, including, suppressing or overriding at the time of the request.
Termcap data is stored as text, making it simple to modify.The text can be retrieved by the termcap library from files or environment variables.
environment variablemay contain a termcap database.It is most often used to store a single termcap description,set by a terminal emulator to provide the terminal's characteristics to the shell and dependent programs.
The original (and most common) implementation of the termcap library retrieves data from a flat text file.Searching a large termcap file, e.g., 500Kb, can be slow.To aid performance, a utility such as reorder is usedto put the most frequently used entries near the beginning of the file.
Newer implementations of termcap store the terminal description in a hashed database,e.g., something like
Berkeley DBversion 1.85.These store two types of records: aliases which point to the canonical entry,and the canonical entry itself.The text of the termcap entry is stored literally.
Limitations and Extensions
The original termcap implementation was designed to use little memory:
* the first name is two characters, to fit in 16 bits
* capability names are two characters
* descriptions are limited to 1023 characters.
* only one description can be included, and must be at the end.
Newer implementations of the termcap interface generally do not require the two-character name at the beginning of the entry.
Capability names are still two characters in all implementations.
The tgetent function used to read the terminal description uses a buffer whose size must be large enough for the data,and is assumed to be 1024 characters.Newer implementations of the termcap interface may relax this constraint by allowing a null pointer in place of the fixed buffer [ [http://www.gnu.org/software/termutils/manual/termcap-1.3/termcap.html The GNU Termcap Library] ] ,or by hiding the data which would not fit, e.g., via the ZZ capability in
NetBSDtermcap. [ [http://www.daemon-systems.org/man/termcap.5.html NetBSD termcap file format] ] The terminfo library interface also emulates the termcap interface, and does not actually use the fixed-size buffer.
The terminfo library's emulation of termcap allows multiple descriptions to be included without restricting the position.A few other newer implementations of the termcap library may also provide this ability, though it is not well-documented. [ [http://freshmeat.net/projects/vi/ Discussion of termcap in vi] ]
curses (programming library)
* [http://invisible-island.net/ncurses/ncurses.faq.html#which_terminfo Current termcap data]
* [http://www.catb.org/~esr/terminfo/ Termcap/Terminfo Resources Page] at
Eric S. Raymond's website
Wikimedia Foundation. 2010.
Look at other dictionaries:
termcap — Terminal Capability Database (UNIX, s. /etc/termcap) … Acronyms
termcap — Terminal Capability Database (UNIX, s. /etc/termcap) … Acronyms von A bis Z
termcap — n. database in UNIX that contains information about the types of terminals in use and character strings to make the terminals perform a particular function (Computers) … English contemporary dictionary
TERMCAP — abbr. TERMinal CAPability (Unix) … United dictionary of abbreviations and acronyms
Terminfo — is a library and database that enables programs to use display terminals in a device independent manner. The origins of this library are from the UNIX System III operating system. Mark Horton implemented the first terminfo library in 1981 1982 as … Wikipedia
Tput — is a standard Unix computer operating system command which is used to set terminal features. Depending on the system, tput uses the terminfo or termcap database, as well as looking into the environment for the terminal type. History Tput was… … Wikipedia
ncurses — based menuconfig Developer(s) GNU Project Stable release 5.9 / 4 April 2011; 7 months ago ( … Wikipedia
Curses (programming library) — curses is a terminal control library for Unix like systems, enabling the construction of text user interface (TUI) applications.Curses is a on the term cursor optimization . It is a library of functions that manage an application s display on… … Wikipedia
Ncurses — Desarrollador Proyecto GNU www.gnu.org/software/ncurses/ncurses.html Información general Última versión estable 5.6 … Wikipedia Español
POSIX terminal interface — The POSIX terminal interface is the generalized abstraction, comprising both an Application Programming Interface for programs, and a set of behavioural expectations for users of a terminal, as defined by the POSIX standard and the Single Unix… … Wikipedia