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.
48 During the 1990s, some users were reluctant to use terminfo in spite of
50 its performance advantages over termcap:
51 · The fixed repertoire prevented users from adding features for unan‐
53 ticipated terminal improvements (or required them to reuse existing
54 capabilities as a workaround).
55 · The limitation to 16-bit signed integers was also mentioned.
57 Because termcap stores everything as a string, it could represent
58 larger numbers.
59 Although termcap's extensibility was rarely used (it was never the
61 speaker who had actually used the feature), the criticism had a point.
62 ncurses 5.0 provided a way to detect nonstandard capabilities, deter‐
63 mine their type and optionally store and retrieve them in a way which
64 did not interfere with other applications. These are referred to as
65 user-defined capabilities because no modifications to the toolset's
66 predefined capability names are needed.
67 The ncurses utilities tic and infocmp have a command-line option “-x”
69 to control whether the nonstandard capabilities are stored or
70 retrieved. A library function use_extended_names is provided for the
71 same purpose.
72 When compiling a terminal database, if “-x” is set, tic will store a
74 user-defined capability if the capability name is not one of the prede‐
75 fined names.
76 Because ncurses provides a termcap library interface, these user-
78 defined capabilities may be visible to termcap applications:
79 · The termcap interface (like all implementations of termcap)
81 requires that the capability names are 2-characters.
82 When the capability is simple enough for use in a termcap applica‐
84 tion, it is provided as a 2-character name.
85 · There are other user-defined capabilities which refer to features
87 not usable in termcap, e.g., parameterized strings that use more
88 than two parameters or use more than the trivial expression support
89 provided by termcap. For these, the terminfo database should have
90 only capability names with 3 or more characters.
91 · Some terminals can send distinct strings for special keys (cursor-,
93 keypad- or function-keys) depending on modifier keys (shift, con‐
94 trol, etc.). While terminfo and termcap have a set of 60 prede‐
95 fined function-key names, to which a series of keys can be
96 assigned, that is insufficient for more than a dozen keys multi‐
97 plied by more than a couple of modifier combinations. The ncurses
98 database uses a convention based on xterm to provide extended spe‐
99 cial-key names.
100 Fitting that into termcap's limitation of 2-character names would
102 be pointless. These extended keys are available only with ter‐
103 minfo.
104 Recognized capabilities
106 The ncurses library uses the user-definable capabilities. While the
107 terminfo database may have other extensions, ncurses makes explicit
108 checks for these:
109 AX boolean, asserts that the terminal interprets SGR 39 and SGR 49
111 by resetting the foreground and background color, respectively,
112 to the default.
113 This is a feature recognized by the screen program as well.
115 E3 string, tells how to clear the terminal's scrollback buffer.
117 When present, the clear(1) program sends this before clearing the
118 terminal.
119 The command “tput clear” does the same thing.
121 RGB
123 boolean, number or string, to assert that the set_a_foreground
124 and set_a_background capabilities correspond to direct colors,
125 using an RGB (red/green/blue) convention. This capability allows
126 the color_content function to return appropriate values without
127 requiring the application to initialize colors using init_color.
128 The capability type determines the values which ncurses sees:
130 boolean
132 implies that the number of bits for red, green and blue are
133 the same. Using the maximum number of colors, ncurses adds
134 two, divides that sum by three, and assigns the result to red,
135 green and blue in that order.
136 If the number of bits needed for the number of colors is not a
138 multiple of three, the blue (and green) components lose in
139 comparison to red.
140 number
142 tells ncurses what result to add to red, green and blue. If
143 ncurses runs out of bits, blue (and green) lose just as in the
144 boolean case.
145 string
147 explicitly list the number of bits used for red, green and
148 blue components as a slash-separated list of decimal integers.
149 Because there are several RGB encodings in use, applications
151 which make assumptions about the number of bits per color are
152 unlikely to work reliably. As a trivial case, for example, one
153 could define RGB#1 to represent the standard eight ANSI colors,
154 i.e., one bit per color.
155 U8 number, asserts that ncurses must use Unicode values for line-
157 drawing characters, and that it should ignore the alternate char‐
158 acter set capabilities when the locale uses UTF-8 encoding. For
159 more information, see the discussion of NCURSES_NO_UTF8_ACS in
160 ncurses(3X).
161 Set this capability to a nonzero value to enable it.
163 XM string, override ncurses's built-in string which enables/disables
165 xterm mouse mode.
166 Extended key-definitions
168 Several terminals provide the ability to send distinct strings for com‐
169 binations of modified special keys. There is no standard for what
170 those keys can send.
171 Since 1999, xterm has supported shift, control, alt, and meta modifiers
173 which produce distinct special-key strings. In a terminal description,
174 ncurses has no special knowledge of the modifiers used. Applications
175 can use the naming convention established for xterm to find these spe‐
176 cial keys in the terminal description.
177 Starting with the curses convention that key names begin with “k” and
179 that shifted special keys are an uppercase name, ncurses' terminal
180 database defines these names to which a suffix is added:
181 Name Description
183 ───────────────────────────────────────────────────────────────
184 kDC special form of kdch1 (delete character)
185 kDN special form of kcud1 (cursor down)
186 kEND special form of kend (End)
187 kHOM special form of khome (Home)
188 kLFT special form of kcub1 (cursor-left or cursor-back)
189 kNXT special form of knext (Next, or Page-Down)
190 kPRV special form of kprev (Prev, or Page-Up)
191 kRIT special form of kcuf1 (cursor-right, or cursor-forward)
192 kUP special form of kcuu1 (cursor-up)
193 These are the suffixes used to denote the modifiers:
195 Value Description
197 ──────────────────────────────────
198 2 Shift
199 3 Alt
200 4 Shift + Alt
202 5 Control
203 6 Shift + Control
204 7 Alt + Control
205 8 Shift + Alt + Control
206 9 Meta
207 10 Meta + Shift
208 11 Meta + Alt
209 12 Meta + Alt + Shift
210 13 Meta + Ctrl
211 14 Meta + Ctrl + Shift
212 15 Meta + Ctrl + Alt
213 16 Meta + Ctrl + Alt + Shift
214 None of these are predefined; terminal descriptions can refer to names
216 which ncurses will allocate at runtime to key-codes. To use these keys
217 in an ncurses program, an application could do this:
218 · using a list of extended key names, ask tigetstr(3X) for their val‐
220 ues, and
221 · given the list of values, ask key_defined(3X) for the key-code
223 which would be returned for those keys by wgetch(3X).
224
226 The “-x” extension feature of tic and infocmp has been adopted in Net‐
227 BSD curses. That implementation stores user-defined capabilities, but
228 makes no use of these capabilities itself.
229
231 tic(1), infocmp(1).
232
234 Thomas E. Dickey
235 beginning with ncurses 5.0 (1999)
236 user_caps(5)