user_caps(5) — Linux manual page


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

       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

       •   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

       •   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

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

           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

                    (meml) lock memory above cursor

                    (memu) unlock memory

                    (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

   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.

             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

             The capability type determines the values which ncurses sees:

                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.

                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.

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

             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

             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%;,
                          %?%p4%t%p3%e%{3}%;%' '%+%c

               xterm+sm+1006|xterm SGR-mouse,
                       kmous=\E[<, XM=\E[?1006;1000%?%p1%{1}%=%th%el%;,

   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
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       ⟨git://⟩ on 2020-11-01.  (At that
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