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term(5) File formats term(5)
term - compiled terminfo terminal description
tic(1) compiles a terminfo terminal type description, and setupterm(3x)
reads it. A compiled description may be stored in a file or in a
database of, potentially, many such descriptions. Further, a compiled
description may be in one of two formats: one similar to that used by
System V, and a newer, extensible format employed exclusively by
ncurses.
Compiled terminfo descriptions are placed under the directory
/usr/share/terminfo. One of two configurations is selected when
building the ncurses libraries.
directory tree
A two-level scheme is used to avoid a linear search of a huge Unix
system directory: /usr/share/terminfo/c/name where name is the
name of the terminal, and c is the first character of name. Thus,
the compiled description of terminal type "act4" is found in the
file /usr/share/terminfo/a/act4. Synonyms for the same terminal
are implemented by multiple links to the same compiled file.
hashed database
Using the Berkeley database API, two types of records are stored:
the terminfo data in the same format as that stored in a directory
tree with the terminal's primary type name as a key, and records
containing only aliases pointing to the primary name.
If built to write hashed databases, ncurses can still read term-
info databases organized as a directory tree, but cannot write
entries into the directory tree. It can write (or rewrite)
entries in the hashed database.
ncurses distinguishes the two cases in the TERMINFO and
TERMINFO_DIRS environment variable by assuming a directory tree
for entries that correspond to an existing directory, and a hashed
database otherwise.
The format has been chosen so that it will be the same on all hardware.
A byte of at least eight bits' width is assumed, but no assumptions
about bit ordering or sign extension are made.
The file is divided into six parts:
(a) header,
(b) terminal names,
(c) Boolean flags,
(d) numbers,
(e) strings, and
(f) a string table.
The header section begins the file. This section contains six short
integers in the format described below. These integers are
(1) the magic number
(octal 0432);
(2) the size,
in bytes, of the terminal names section;
(3) the number of bytes in the Boolean flags section;
(4) the number of short integers in the numbers section;
(5) the number of offsets
(short integers) in the strings section;
(6) the size,
in bytes, of the string table.
The capabilities in the Boolean flags, numbers, and strings sections
are in the same order as in the header file term.h.
Short integers are signed, in the range -32768 to 32767, and stored in
little-endian format.
Numbers in a terminal description, whether they are entries in the
numbers or strings table, are positive integers. Boolean flags are
treated as positive one-byte integers. In each case, those positive
integers represent a terminal capability. The terminal compiler tic
uses negative integers to handle the cases where a capability is not
available:
o If a capability is absent from this terminal, tic stores a -1 in
the corresponding table.
The integer value -1 is represented by two bytes 0377, 0377.
Absent Boolean values are represented by the byte 0 (false).
o If a capability has been canceled from this terminal, tic stores a
-2 in the corresponding table.
The integer value -2 is represented by two bytes 0377, 0376.
The Boolean value -2 is represented by the byte 0376.
o Other negative values are illegal.
The terminal names section comes after the header. It contains the
first line of the terminfo description, listing the various names for
the terminal, separated by the "|" character. The terminal names
section is terminated with an ASCII NUL character.
The Boolean flags section has one byte for each flag. Boolean
capabilities are either 1 or 0 (true or false) according to whether the
terminal supports the given capability or not.
Between the Boolean flags section and the number section, a null byte
will be inserted, if necessary, to ensure that the number section
begins on an even byte This is a relic of the PDP-11's word-addressed
architecture, originally designed to avoid traps induced by addressing
a word on an odd byte boundary. All short integers are aligned on a
short word boundary.
The numbers section is similar to the Boolean flags section. Each
capability takes up two bytes, and is stored as a little-endian short
integer.
The strings section is also similar. Each capability is stored as a
short integer. The capability value is an index into the string table.
The string table is the last section. It contains all of the values of
string capabilities referenced in the strings section. Each string is
null-terminated. Special characters in ^X or \c notation are stored in
their interpreted form, not the printing representation. Padding
information $<nn> and parameter information %x are stored intact in
uninterpreted form.
The previous section describes the conventional terminfo binary format.
With some minor variations of the offsets (see PORTABILITY), the same
binary format is used in all modern Unix systems. Each system uses a
predefined set of Boolean, number or string capabilities.
The ncurses libraries and applications support extended terminfo binary
format, allowing users to define capabilities that are loaded at
runtime. This extension is made possible by using the fact that the
other implementations stop reading the terminfo data when they reach
the end of the size given in the header. ncurses checks the size, and
if it exceeds that due to the predefined data, continues to parse
according to its own scheme.
First, it reads the extended header (5 short integers):
(1) count of extended Boolean capabilities
(2) count of extended numeric capabilities
(3) count of extended string capabilities
(4) count of the items in extended string table
(5) size of the extended string table in bytes
The count- and size-values for the extended string table include the
extended capability names as well as extended capability values.
Using the counts and sizes, ncurses allocates arrays and reads data for
the extended capabilities in the same order as the header information.
The extended string table contains values for string capabilities.
After the end of these values, it contains the names for each of the
extended capabilities in order: Boolean, numeric, and string.
By storing terminal descriptions in this way, ncurses is able to
provide a database useful with legacy applications, as well as
providing data for applications that require more information about a
terminal type than was anticipated by X/Open Curses. See user_caps(5)
for an overview of the way ncurses uses this extended information.
Applications that manipulate terminal data can use the definitions
described in term_variables(3x) associating the long capability names
with members of a TERMTYPE structure.
On occasion, 16-bit signed integers are not large enough. ncurses 6.1
introduced a new format by making a few changes to the legacy format:
o a different magic number (octal 01036)
o changing the type for the number array from signed 16-bit integers
to signed 32-bit integers.
To maintain compatibility, the library presents the same data
structures to direct users of the TERMTYPE structure as in previous
formats. However, that cannot provide callers with the extended
numbers. The library uses a similar but hidden data structure
TERMTYPE2 to provide data for the terminfo functions.
/usr/share/terminfo
compiled terminal description database
Note that it is possible for setupterm to expect a different set of
capabilities than are actually present in the file. Either the
database may have been updated since setupterm was recompiled
(resulting in extra unrecognized entries in the file) or the program
may have been recompiled more recently than the database was updated
(resulting in missing entries). The routine setupterm must be prepared
for both possibilities - this is why the numbers and sizes are
included. Also, new capabilities must always be added at the end of
the lists of Boolean, number, and string capabilities.
X/Open Curses does not specify a format for the terminfo database.
System V curses used a directory-tree of binary files, one per terminal
description.
Despite the consistent use of little-endian numbers and the otherwise
self-describing format, it is not wise to count on portability of
binary terminfo entries between commercial Unix versions. The problem
is that there are at least three versions of terminfo (under HP-UX,
AIX, and OSF/1) each of which diverged from System V terminfo after
SVr1, and added extension capabilities to the string table that (in the
binary format) collide with System V and X/Open Curses extensions. See
terminfo(5) for detailed discussion of terminfo source compatibility
issues.
This implementation is by default compatible with the binary terminfo
format used by Solaris curses, except in a few less-used details where
it was found that the latter did not match X/Open Curses. The format
used by the other Unix versions can be matched by building ncurses with
different configuration options.
The magic number in a binary terminfo file is the first 16 bits (two
bytes). Besides making it more reliable for the library to check that
a file is terminfo, utilities such as file(1) also use that to tell
what the file-format is. System V defined more than one magic number,
with 0433, 0435 as screen-dumps (see scr_dump(5)). This implementation
uses 01036 as a continuation of that sequence, but with a different
high-order byte to avoid confusion.
The TERMTYPE Structure
Direct access to the TERMTYPE structure is provided for legacy
applications. Portable applications should use tigetflag(3x) and
related functions to read terminal capabilities.
A small number of terminal descriptions use uppercase characters in
their names. If the underlying file system ignores the difference
between uppercase and lowercase, ncurses represents the "first
character" of the terminal name used as the intermediate level of a
directory tree in (two-character) hexadecimal form.
ncurses stores compiled terminal descriptions in three related formats,
described in the subsections
o Legacy Storage Format, and
o Extended Storage Format, and
o Extended Number Format.
The legacy storage format and the extended number format differ by the
types of numeric capability that they can store (for example, 16-
versus 32-bit integers). The extended storage format introduced by
ncurses 5.0 adds data to either of these formats.
Some limitations apply:
o total compiled entries cannot exceed 4096 bytes in the legacy
format.
o total compiled entries cannot exceed 32768 bytes in the extended
format.
o the name field cannot exceed 128 bytes.
Compiled entries are limited to 32768 bytes because offsets into the
strings table use two-byte integers. The legacy format could have
supported 32768-byte entries, but was limited to a virtual memory
page's 4096 bytes.
Here is a terminfo description of the Lear-Siegler ADM-3, a popular
though rather stupid early terminal.
adm3a|lsi adm3a,
am,
cols#80, lines#24,
bel=^G, clear=\032$<1>, cr=^M, cub1=^H, cud1=^J,
cuf1=^L, cup=\E=%p1%{32}%+%c%p2%{32}%+%c, cuu1=^K,
home=^^, ind=^J,
A hexadecimal dump of its compiled terminal description (in legacy
format) follows.
0000 1a 01 10 00 02 00 03 00 82 00 31 00 61 64 6d 33 ........ ..1.adm3
0010 61 7c 6c 73 69 20 61 64 6d 33 61 00 00 01 50 00 a|lsi ad m3a...P.
0020 ff ff 18 00 ff ff 00 00 02 00 ff ff ff ff 04 00 ........ ........
0030 ff ff ff ff ff ff ff ff 0a 00 25 00 27 00 ff ff ........ ..%.'...
0040 29 00 ff ff ff ff 2b 00 ff ff 2d 00 ff ff ff ff ).....+. ..-.....
0050 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0060 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0070 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0080 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0090 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00a0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00b0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00c0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00d0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00e0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
00f0 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0100 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0110 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........ ........
0120 ff ff ff ff ff ff 2f 00 07 00 0d 00 1a 24 3c 31 ....../. .....$<1
0130 3e 00 1b 3d 25 70 31 25 7b 33 32 7d 25 2b 25 63 >..=%p1% {32}%+%c
0140 25 70 32 25 7b 33 32 7d 25 2b 25 63 00 0a 00 1e %p2%{32} %+%c....
0150 00 08 00 0c 00 0b 00 0a 00 ........ .
Thomas E. Dickey
extended terminfo format for ncurses 5.0
hashed database support for ncurses 5.6
extended number support for ncurses 6.1
Eric S. Raymond
documented legacy terminfo format (that used by pcurses).
curses(3x), curs_terminfo(3x), terminfo(5), user_caps(5)
ncurses 6.5 2024-06-15 term(5)