Ubuntu Manpage: term - compiled terminfo terminal description

Provided by: ncurses-bin_6.4+20240113-1ubuntu2_amd64

NAME

       term - compiled terminfo terminal description

SYNOPSIS

       term

DESCRIPTION

Storage Location
Compiled terminfo descriptions are placed under the directory /etc/terminfo. Two configurations are
supported (when building the ncurses libraries):

directory tree
A two-level scheme is used to avoid a linear search of a huge Unix system directory:
/etc/terminfo/c/name where name is the name of the terminal, and c is the first character of name.
Thus, act4 can be found in the file /etc/terminfo/a/act4. Synonyms for the same terminal are
implemented by multiple links to the same compiled file.

hashed database
Using Berkeley database, two types of records are stored: the terminfo data in the same format as
stored in a directory tree with the terminfo's primary name as a key, and records containing only
aliases pointing to the primary name.

If built to write hashed databases, ncurses can still read terminfo 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 hashed database
otherwise.

Legacy Storage Format
The format has been chosen so that it will be the same on all hardware. An 8 or more bit byte is
assumed, but no assumptions about byte ordering or sign extension are made.

The compiled file is created with the tic program, and read by the routine setupterm(3NCURSES). The file
is divided into six parts:

a) header,

b) terminal names,

c) Boolean flags,

d) numbers,

e) strings, and

f) 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 the file
<term.h>.

Short integers are signed, in the range -32768 to 32767. They are stored as two 8-bit bytes. The first
byte contains the least significant 8 bits of the value, and the second byte contains the most
significant 8 bits. (Thus, the value represented is 256*second+first.) This format corresponds to the
hardware of the VAX and PDP-11 (that is, little-endian machines). Machines where this does not
correspond to the hardware must read the integers as two bytes and compute the little-endian value.

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:

• 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).

• 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.

• 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.

Extended Storage Format
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 which are loaded at runtime. This extension is made possible by using the fact that the
other implementations stop reading the terminfo data when they have reached 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, e.g., Booleans, then numbers and
finally strings.

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 which need more than the predefined
capabilities. See user_caps(5) for an overview of the way ncurses uses this extended information.

Applications which manipulate terminal data can use the definitions described in
terminfo_variables(3NCURSES) which associate the long capability names with members of a TERMTYPE
structure.

Extended Number Format
On occasion, 16-bit signed integers are not large enough. With ncurses 6.1, a new format was introduced
by making a few changes to the legacy format:

• a different magic number (octal 01036)

• 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.

FILES

       /etc/terminfo
              compiled terminal description database

PORTABILITY

setupterm
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.

Binary Format
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 for 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) which
diverged from System V terminfo after SVr1, and have added extension capabilities to the string table
that (in the binary format) collide with System V and XSI 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.

Magic Codes
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 the tigetflag and related functions described in terminfo(3NCURSES) for reading terminal
capabilities.

Mixed-case Terminal Names
A small number of terminal descriptions use uppercase characters in their names. If the underlying
filesystem 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.

Limits
ncurses stores compiled terminal descriptions in three related formats, described in the sections

• LEGACY STORAGE FORMAT, and

• EXTENDED STORAGE FORMAT, and

• EXTENDED NUMBER FORMAT.

The legacy storage format and the extended number format differ by the types of numeric capability which
they can store (i.e., 16-bit versus 32-bit integers). The extended storage format introduced by ncurses
5.0 adds data to either of these formats.

Some limitations apply:

• total compiled entries cannot exceed 4096 bytes in the legacy format.

• total compiled entries cannot exceed 32768 bytes in the extended format.

• 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.

EXAMPLES

       As  an  example,  here  is a description for 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,

       and a hexadecimal dump of the compiled terminal description:

       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                       ........ .

AUTHORS

       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, e.g., from pcurses.