user_caps(5) — Linux manual page

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.  For
           example, ncurses can be configured with tables which match
           the terminal databases for AIX, HP-UX or OSF/1, rather than
           the default Solaris-like configuration.

       •   In SVr4 curses and ncurses, the terminal database is defined
           at compile-time using a text file which lists the different
           terminal capabilities.

           In principle, the text-file can be extended, but doing this
           requires recompiling and reinstalling the library.  The text-
           file used in ncurses for terminal capabilities includes
           details for various systems past the documented X/Open Curses
           features.  For example, ncurses supports these capabilities
           in each configuration:

               memory_lock
                    (meml) lock memory above cursor

               memory_unlock
                    (memu) unlock memory

               box_chars_1
                    (box1) box characters primary set

           The memory lock/unlock capabilities were included because
           they were used in the X11R6 terminal description for xterm.
           The box1 capability is used in @TIC@ to help with terminal
           descriptions written for AIX.

       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.

             Because there are several RGB encodings in use,
             applications which make assumptions about the number of
             bits per color are unlikely to work reliably.  As a trivial
             case, for example, one could define RGB#1 to represent the
             standard eight ANSI colors, i.e., one bit per color.

          U8 number, 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.

             ncurses sends a character sequence to the terminal to
             initialize mouse mode, and when the user clicks the mouse
             buttons or (in certain modes) moves the mouse, handles the
             characters sent back by the terminal to tell it what was
             done with the mouse.

             The mouse protocol is enabled when the mask passed in the
             mousemask function is nonzero.  By default, ncurses handles
             the responses for the X11 xterm mouse protocol.  It also
             knows about the SGR 1006 xterm mouse protocol, but must to
             be told to look for this specifically.  It will not be able
             to guess which mode is used, because the responses are
             enough alike that only confusion would result.

             The XM capability has a single parameter.  If nonzero, the
             mouse protocol should be enabled.  If zero, the mouse
             protocol should be disabled.  ncurses inspects this
             capability if it is present, to see whether the 1006
             protocol is used.  If so, it expects the responses to use
             the SGR 1006 xterm mouse protocol.

             The xterm mouse protocol is used by other terminal
             emulators.  The terminal database uses building-blocks for
             the various xterm mouse protocols which can be used in
             customized terminal descriptions.

             The terminal database building blocks for this mouse
             feature also have an experimental capability xm.  The “xm”
             capability describes the mouse response.  Currently there
             is no interpreter which would use this information to make
             the mouse support completely data-driven.

             xm shows the format of the mouse responses.  In this
             experimental capability, the parameters are

               p1   y-ordinate

               p2   x-ordinate

               p3   button

               p4   state, e.g., pressed or released

               p5   y-ordinate starting region

               p6   x-ordinate starting region

               p7   y-ordinate ending region

               p8   x-ordinate ending region

             Here are examples from the terminal database for the most
             commonly used xterm mouse protocols:

               xterm+x11mouse|X11 xterm mouse protocol,
                       kmous=\E[M, XM=\E[?1000%?%p1%{1}%=%th%el%;,
                       xm=\E[M
                          %?%p4%t%p3%e%{3}%;%' '%+%c
                          %p2%'!'%+%c
                          %p1%'!'%+%c,

               xterm+sm+1006|xterm SGR-mouse,
                       kmous=\E[<, XM=\E[?1006;1000%?%p1%{1}%=%th%el%;,
                       xm=\E[<%i%p3%d;
                          %p1%d;
                          %p2%d;
                          %?%p4%tM%em%;,

   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@(1M), @INFOCMP@(1M).

       The terminal database section NCURSES USER-DEFINABLE CAPABILITIES
       summarizes commonly-used user-defined capabilities which are used
       in the terminal descriptions.  Some of those features are
       mentioned in screen(1) or tmux(1).

       XTerm Control Sequences provides further information on the xterm
       features which are used in these extended capabilities.

AUTHORS         top

       Thomas E. Dickey
       beginning with ncurses 5.0 (1999)

COLOPHON         top

       This page is part of the ncurses (new curses) project.
       Information about the project can be found at 
       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have
       a bug report for this manual page, send it to
       bug-ncurses-request@gnu.org.  This page was obtained from the
       project's upstream Git mirror of the CVS repository
       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2020-12-18.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2020-12-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

                                                            user_caps(5)

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