NAME | SYNOPSIS | DESCRIPTION | PORTABILITY | SEE ALSO | AUTHORS | COLOPHON

user_caps(5)                 File Formats Manual                user_caps(5)

NAME         top

       user_caps - user-defined terminfo capabilities

SYNOPSIS         top

       tic -x, infocmp -x

DESCRIPTION         top

   Background
       Before ncurses 5.0, terminfo databases used a fixed repertoire of
       terminal capabilities designed for the SVr2 terminal database in
       1984, and extended in stages through SVr4 (1989), and standardized in
       the Single Unix Specification beginning in 1995.

       Most of the extensions in this fixed repertoire were additions to the
       tables of boolean, numeric and string capabilities.  Rather than
       change the meaning of an existing capability, a new name was added.
       The terminfo database uses a binary format; binary compatibility was
       ensured by using a header which gave the number of items in the
       tables for each type of capability.  The standardization was
       incomplete:

       ·   The binary format itself is not described in the X/Open Curses
           documentation.  Only the source format is described.

           Library developers rely upon the SVr4 documentation, and reverse-
           engineering the compiled terminfo files to match the binary
           format.

       ·   Lacking a standard for the binary format, most implementations
           copy the SVr2 binary format, which uses 16-bit signed integers,
           and is limited to 4096-byte entries.

           The format cannot represent very large numeric capabilities, nor
           can it represent large numbers of special keyboard definitions.

       ·   The tables of capability names differ between implementations.

           Although they may provide all of the standard capability names,
           the position in the tables differs because some features were
           added as needed, while others were added (out of order) to comply
           with X/Open Curses.

           While ncurses' repertoire of predefined capabilities is closest
           to Solaris, Solaris's terminfo database has a few differences
           from the list published by X/Open Curses.

       During the 1990s, some users were reluctant to use terminfo in spite
       of its performance advantages over termcap:

       ·   The fixed repertoire prevented users from adding features for
           unanticipated terminal improvements (or required them to reuse
           existing capabilities as a workaround).

       ·   The limitation to 16-bit signed integers was also mentioned.
           Because termcap stores everything as a string, it could represent
           larger numbers.

       Although termcap's extensibility was rarely used (it was never the
       speaker who had actually used the feature), the criticism had a
       point.  ncurses 5.0 provided a way to detect nonstandard
       capabilities, determine their type and optionally store and retrieve
       them in a way which did not interfere with other applications.  These
       are referred to as user-defined capabilities because no modifications
       to the toolset's predefined capability names are needed.

       The ncurses utilities tic and infocmp have a command-line option “-x”
       to control whether the nonstandard capabilities are stored or
       retrieved.  A library function use_extended_names is provided for the
       same purpose.

       When compiling a terminal database, if “-x” is set, tic will store a
       user-defined capability if the capability name is not one of the
       predefined names.

       Because ncurses provides a termcap library interface, these user-
       defined capabilities may be visible to termcap applications:

       ·   The termcap interface (like all implementations of termcap)
           requires that the capability names are 2-characters.

           When the capability is simple enough for use in a termcap
           application, it is provided as a 2-character name.

       ·   There are other user-defined capabilities which refer to features
           not usable in termcap, e.g., parameterized strings that use more
           than two parameters or use more than the trivial expression
           support provided by termcap.  For these, the terminfo database
           should have only capability names with 3 or more characters.

       ·   Some terminals can send distinct strings for special keys
           (cursor-, keypad- or function-keys) depending on modifier keys
           (shift, control, etc.).  While terminfo and termcap have a set of
           60 predefined function-key names, to which a series of keys can
           be assigned, that is insufficient for more than a dozen keys
           multiplied by more than a couple of modifier combinations.  The
           ncurses database uses a convention based on xterm to provide
           extended special-key names.

           Fitting that into termcap's limitation of 2-character names would
           be pointless.  These extended keys are available only with
           terminfo.

   Recognized capabilities
       The ncurses library uses the user-definable capabilities.  While the
       terminfo database may have other extensions, ncurses makes explicit
       checks for these:

          AX boolean, asserts that the terminal interprets SGR 39 and SGR 49
             by resetting the foreground and background color, respectively,
             to the default.

             This is a feature recognized by the screen program as well.

          E3 string, tells how to clear the terminal's scrollback buffer.
             When present, the clear(1) program sends this before clearing
             the terminal.

             The command “tput clear” does the same thing.

          RGB
             boolean, number or string, to assert that the set_a_foreground
             and set_a_background capabilities correspond to direct colors,
             using an RGB (red/green/blue) convention.  This capability
             allows the color_content function to return appropriate values
             without requiring the application to initialize colors using
             init_color.

             The capability type determines the values which ncurses sees:

             boolean
                implies that the number of bits for red, green and blue are
                the same.  Using the maximum number of colors, ncurses adds
                two, divides that sum by three, and assigns the result to
                red, green and blue in that order.

                If the number of bits needed for the number of colors is not
                a multiple of three, the blue (and green) components lose in
                comparison to red.

             number
                tells ncurses what result to add to red, green and blue.  If
                ncurses runs out of bits, blue (and green) lose just as in
                the boolean case.

             string
                explicitly list the number of bits used for red, green and
                blue components as a slash-separated list of decimal
                integers.

          U8 boolean, asserts that ncurses must use Unicode values for line-
             drawing characters, and that it should ignore the alternate
             character set capabilities when the locale uses UTF-8 encoding.
             For more information, see the discussion of NCURSES_NO_UTF8_ACS
             in ncurses(3X).

             Set this capability to a nonzero value to enable it.

          XM string, override ncurses's built-in string which
             enables/disables xterm mouse mode.

   Extended key-definitions
       Several terminals provide the ability to send distinct strings for
       combinations of modified special keys.  There is no standard for what
       those keys can send.

       Since 1999, xterm has supported shift, control, alt, and meta
       modifiers which produce distinct special-key strings.  In a terminal
       description, ncurses has no special knowledge of the modifiers used.
       Applications can use the naming convention established for xterm to
       find these special keys in the terminal description.

       Starting with the curses convention that key names begin with “k” and
       that shifted special keys are an uppercase name, ncurses' terminal
       database defines these names to which a suffix is added:

            Name   Description
            ───────────────────────────────────────────────────────────────
            kDC    special form of kdch1 (delete character)
            kDN    special form of kcud1 (cursor down)
            kEND   special form of kend (End)
            kHOM   special form of khome (Home)
            kLFT   special form of kcub1 (cursor-left or cursor-back)
            kNXT   special form of knext (Next, or Page-Down)
            kPRV   special form of kprev (Prev, or Page-Up)
            kRIT   special form of kcuf1 (cursor-right, or cursor-forward)
            kUP    special form of kcuu1 (cursor-up)

       These are the suffixes used to denote the modifiers:

            Value   Description
            ──────────────────────────────────
            2       Shift
            3       Alt
            4       Shift + Alt
            5       Control

            6       Shift + Control
            7       Alt + Control
            8       Shift + Alt + Control
            9       Meta
            10      Meta + Shift
            11      Meta + Alt
            12      Meta + Alt + Shift
            13      Meta + Ctrl
            14      Meta + Ctrl + Shift
            15      Meta + Ctrl + Alt
            16      Meta + Ctrl + Alt + Shift

       None of these are predefined; terminal descriptions can refer to
       names which ncurses will allocate at runtime to key-codes.  To use
       these keys in an ncurses program, an application could do this:

       ·   using a list of extended key names, ask tigetstr(3X) for their
           values, and

       ·   given the list of values, ask key_defined(3X) for the key-code
           which would be returned for those keys by wgetch(3X).

PORTABILITY         top

       The “-x” extension feature of tic and infocmp has been adopted in
       NetBSD curses.  That implementation stores user-defined capabilities,
       but makes no use of these capabilities itself.

SEE ALSO         top

       tic(1), infocmp(1).

AUTHORS         top

       Thomas E. Dickey
       beginning with ncurses 5.0 (1999)

COLOPHON         top

       This page is part of the ncurses (new curses) project.  Information
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       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have a
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       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2017-11-25.  (At that
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                                                                user_caps(5)

Pages that refer to this page: ncurses(3x)terminfo(5)