1user_caps(5) File Formats Manual user_caps(5)
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6 user_caps - user-defined terminfo capabilities
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9 tic -x, infocmp -x
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12 Background
13 Before ncurses 5.0, terminfo databases used a fixed repertoire of ter‐
14 minal capabilities designed for the SVr2 terminal database in 1984, and
15 extended in stages through SVr4 (1989), and standardized in the Single
16 Unix Specification beginning in 1995.
17 Most of the extensions in this fixed repertoire were additions to the
19 tables of boolean, numeric and string capabilities. Rather than change
20 the meaning of an existing capability, a new name was added. The ter‐
21 minfo database uses a binary format; binary compatibility was ensured
22 by using a header which gave the number of items in the tables for each
23 type of capability. The standardization was incomplete:
24 · The binary format itself is not described in the X/Open Curses doc‐
26 umentation. Only the source format is described.
27 Library developers rely upon the SVr4 documentation, and reverse-
29 engineering the compiled terminfo files to match the binary format.
30 · Lacking a standard for the binary format, most implementations copy
32 the SVr2 binary format, which uses 16-bit signed integers, and is
33 limited to 4096-byte entries.
34 The format cannot represent very large numeric capabilities, nor
36 can it represent large numbers of special keyboard definitions.
37 · The tables of capability names differ between implementations.
39 Although they may provide all of the standard capability names, the
41 position in the tables differs because some features were added as
42 needed, while others were added (out of order) to comply with
43 X/Open Curses.
44 While ncurses' repertoire of predefined capabilities is closest to
46 Solaris, Solaris's terminfo database has a few differences from the
47 list published by X/Open Curses. For example, ncurses can be con‐
48 figured with tables which match the terminal databases for AIX, HP-
49 UX or OSF/1, rather than the default Solaris-like configuration.
50 · In SVr4 curses and ncurses, the terminal database is defined at
52 compile-time using a text file which lists the different terminal
53 capabilities.
54 In principle, the text-file can be extended, but doing this
56 requires recompiling and reinstalling the library. The text-file
57 used in ncurses for terminal capabilities includes details for var‐
58 ious systems past the documented X/Open Curses features. For exam‐
59 ple, ncurses supports these capabilities in each configuration:
60 memory_lock
62 (meml) lock memory above cursor
63 memory_unlock
65 (memu) unlock memory
66 box_chars_1
68 (box1) box characters primary set
69 The memory lock/unlock capabilities were included because they were
71 used in the X11R6 terminal description for xterm. The box1 capa‐
72 bility is used in tic to help with terminal descriptions written
73 for AIX.
74 During the 1990s, some users were reluctant to use terminfo in spite of
76 its performance advantages over termcap:
77 · The fixed repertoire prevented users from adding features for unan‐
79 ticipated terminal improvements (or required them to reuse existing
80 capabilities as a workaround).
81 · The limitation to 16-bit signed integers was also mentioned.
83 Because termcap stores everything as a string, it could represent
84 larger numbers.
85 Although termcap's extensibility was rarely used (it was never the
87 speaker who had actually used the feature), the criticism had a point.
88 ncurses 5.0 provided a way to detect nonstandard capabilities, deter‐
89 mine their type and optionally store and retrieve them in a way which
90 did not interfere with other applications. These are referred to as
91 user-defined capabilities because no modifications to the toolset's
92 predefined capability names are needed.
93 The ncurses utilities tic and infocmp have a command-line option “-x”
95 to control whether the nonstandard capabilities are stored or
96 retrieved. A library function use_extended_names is provided for the
97 same purpose.
98 When compiling a terminal database, if “-x” is set, tic will store a
100 user-defined capability if the capability name is not one of the prede‐
101 fined names.
102 Because ncurses provides a termcap library interface, these user-
104 defined capabilities may be visible to termcap applications:
105 · The termcap interface (like all implementations of termcap)
107 requires that the capability names are 2-characters.
108 When the capability is simple enough for use in a termcap applica‐
110 tion, it is provided as a 2-character name.
111 · There are other user-defined capabilities which refer to features
113 not usable in termcap, e.g., parameterized strings that use more
114 than two parameters or use more than the trivial expression support
115 provided by termcap. For these, the terminfo database should have
116 only capability names with 3 or more characters.
117 · Some terminals can send distinct strings for special keys (cursor-,
119 keypad- or function-keys) depending on modifier keys (shift, con‐
120 trol, etc.). While terminfo and termcap have a set of 60 prede‐
121 fined function-key names, to which a series of keys can be
122 assigned, that is insufficient for more than a dozen keys multi‐
123 plied by more than a couple of modifier combinations. The ncurses
124 database uses a convention based on xterm to provide extended spe‐
125 cial-key names.
126 Fitting that into termcap's limitation of 2-character names would
128 be pointless. These extended keys are available only with ter‐
129 minfo.
130 Recognized capabilities
132 The ncurses library uses the user-definable capabilities. While the
133 terminfo database may have other extensions, ncurses makes explicit
134 checks for these:
135 AX boolean, asserts that the terminal interprets SGR 39 and SGR 49
137 by resetting the foreground and background color, respectively,
138 to the default.
139 This is a feature recognized by the screen program as well.
141 E3 string, tells how to clear the terminal's scrollback buffer.
143 When present, the clear(1) program sends this before clearing the
144 terminal.
145 The command “tput clear” does the same thing.
147 RGB
149 boolean, number or string, to assert that the set_a_foreground
150 and set_a_background capabilities correspond to direct colors,
151 using an RGB (red/green/blue) convention. This capability allows
152 the color_content function to return appropriate values without
153 requiring the application to initialize colors using init_color.
154 The capability type determines the values which ncurses sees:
156 boolean
158 implies that the number of bits for red, green and blue are
159 the same. Using the maximum number of colors, ncurses adds
160 two, divides that sum by three, and assigns the result to red,
161 green and blue in that order.
162 If the number of bits needed for the number of colors is not a
164 multiple of three, the blue (and green) components lose in
165 comparison to red.
166 number
168 tells ncurses what result to add to red, green and blue. If
169 ncurses runs out of bits, blue (and green) lose just as in the
170 boolean case.
171 string
173 explicitly list the number of bits used for red, green and
174 blue components as a slash-separated list of decimal integers.
175 Because there are several RGB encodings in use, applications
177 which make assumptions about the number of bits per color are
178 unlikely to work reliably. As a trivial case, for example, one
179 could define RGB#1 to represent the standard eight ANSI colors,
180 i.e., one bit per color.
181 U8 number, asserts that ncurses must use Unicode values for line-
183 drawing characters, and that it should ignore the alternate char‐
184 acter set capabilities when the locale uses UTF-8 encoding. For
185 more information, see the discussion of NCURSES_NO_UTF8_ACS in
186 ncurses(3X).
187 Set this capability to a nonzero value to enable it.
189 XM string, override ncurses's built-in string which enables/disables
191 xterm mouse mode.
192 Extended key-definitions
194 Several terminals provide the ability to send distinct strings for com‐
195 binations of modified special keys. There is no standard for what
196 those keys can send.
197 Since 1999, xterm has supported shift, control, alt, and meta modifiers
199 which produce distinct special-key strings. In a terminal description,
200 ncurses has no special knowledge of the modifiers used. Applications
201 can use the naming convention established for xterm to find these spe‐
202 cial keys in the terminal description.
203 Starting with the curses convention that key names begin with “k” and
205 that shifted special keys are an uppercase name, ncurses' terminal
206 database defines these names to which a suffix is added:
207 Name Description
209 ───────────────────────────────────────────────────────────────
210 kDC special form of kdch1 (delete character)
211 kDN special form of kcud1 (cursor down)
212 kEND special form of kend (End)
213 kHOM special form of khome (Home)
214 kLFT special form of kcub1 (cursor-left or cursor-back)
215 kNXT special form of knext (Next, or Page-Down)
216 kPRV special form of kprev (Prev, or Page-Up)
217 kRIT special form of kcuf1 (cursor-right, or cursor-forward)
218 kUP special form of kcuu1 (cursor-up)
219 These are the suffixes used to denote the modifiers:
221 Value Description
223 ──────────────────────────────────
224 2 Shift
225 3 Alt
226 4 Shift + Alt
227 5 Control
228 6 Shift + Control
229 7 Alt + Control
230 8 Shift + Alt + Control
231 9 Meta
232 10 Meta + Shift
233 11 Meta + Alt
234 12 Meta + Alt + Shift
235 13 Meta + Ctrl
236 14 Meta + Ctrl + Shift
237 15 Meta + Ctrl + Alt
238 16 Meta + Ctrl + Alt + Shift
239 None of these are predefined; terminal descriptions can refer to names
241 which ncurses will allocate at runtime to key-codes. To use these keys
242 in an ncurses program, an application could do this:
243 · using a list of extended key names, ask tigetstr(3X) for their val‐
245 ues, and
246 · given the list of values, ask key_defined(3X) for the key-code
248 which would be returned for those keys by wgetch(3X).
249
251 The “-x” extension feature of tic and infocmp has been adopted in Net‐
252 BSD curses. That implementation stores user-defined capabilities, but
253 makes no use of these capabilities itself.
254
256 tic(1M), infocmp(1M).
257
259 Thomas E. Dickey
260 beginning with ncurses 5.0 (1999)
261 user_caps(5)