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ncurses/man/term.5
Thomas E. Dickey 45e78e514f
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'\" t
.\"***************************************************************************
.\" Copyright 2018-2024,2025 Thomas E. Dickey *
.\" Copyright 1998-2016,2017 Free Software Foundation, Inc. *
.\" *
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.\"
.\" $Id: term.5,v 1.85 2025/08/16 19:11:47 tom Exp $
.TH term 5 2025-08-16 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "File formats"
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.SH NAME
term \-
compiled \fI\%term\%info\fP terminal description
.\"SH SYNOPSIS
.SH DESCRIPTION
\fB\%@TIC@\fP(1) compiles a
.I \%term\%info
terminal type description,
and \fB\%setupterm\fP(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
.IR \%ncurses .
.SS "Storage Location"
Compiled
.I \%term\%info descriptions are placed
under the directory
.IR \%@TERMINFO@ .
One of two configurations is selected
when building the
.I \%ncurses
libraries.
.TP 5
.B directory tree
A two-level scheme is used to avoid a linear search
of a huge Unix system directory:
.IR \%@TERMINFO@/ c / name
where
.I name
is the name of the terminal,
and
.I c
is the first character of
.IR name .
Thus,
the compiled description of terminal type \*(``act4\*(''
is found in the file
.IR \%@TERMINFO@/a/act4 .
Synonyms for the same terminal are implemented by multiple
links to the same compiled file.
.TP 5
.B hashed database
Using the Berkeley database API,
two types of records are stored:
the
.I \%term\%info
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.
.IP
If built to write hashed databases,
.I \%ncurses
can still read
.I \%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.
.IP
.I \%ncurses
distinguishes the two cases in the
.I \%TERMINFO
and
.I \%TERMINFO_DIRS
environment variable by assuming a directory tree for entries that
correspond to an existing directory,
and a hashed database otherwise.
.SS "Legacy Storage Format"
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.
.PP
The file is divided into six parts:
.RS 5
.IP (a) 4
.IR header ,
.IP (b)
.IR "terminal names" ,
.IP (c)
.IR "Boolean flags" ,
.IP (d)
.IR numbers ,
.IP (e)
.IR strings ,
and
.IP (f)
a
.IR "string table" .
.RE
.PP
The \fIheader\fP section begins the file.
This section contains six short integers in the format
described below.
These integers are
.RS 5
.TP 5
(1) the \fImagic number\fP
(octal 0432);
.TP 5
(2) the size,
in bytes,
of the \fIterminal names\fP section;
.TP 5
(3) the number of bytes in the \fIBoolean flags\fP section;
.TP 5
(4) the number of short integers in the \fInumbers\fP section;
.TP 5
(5) the number of offsets
(short integers)
in the \fIstrings\fP section;
.TP 5
(6) the size,
in bytes,
of the \fIstring table\fP.
.RE
.PP
The capabilities in the
\fIBoolean flags\fP,
\fInumbers\fP,
and
\fIstrings\fP
sections are in the same order as in the header file
.IR term.h .
.PP
Short integers are signed,
in the range \-32768 to 32767,
and stored in little-endian format.
.PP
Numbers in a terminal description,
whether they are entries in the \fInumbers\fP or \fIstrings\fP 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
.I \%@TIC@
uses negative integers to handle the cases where a capability is not
available:
.bP
If a capability is absent from this terminal,
.I \%@TIC@
stores a \-1 in the corresponding table.
.IP
The integer value \-1 is represented by two bytes 0377,
0377.
.br
Absent Boolean values are represented by the byte 0 (false).
.bP
If a capability has been canceled from this terminal,
.I \%@TIC@
stores a \-2 in the corresponding table.
.IP
The integer value \-2 is represented by two bytes 0377,
0376.
.br
The Boolean value \-2 is represented by the byte 0376.
.br
.bP
Other negative values are illegal.
.PP
The \fIterminal names\fP section comes after the \fIheader\fP.
It contains the first line of the
.I \%term\%info
description,
listing the various names for the terminal,
separated by the \*(``|\*('' character.
The \fIterminal names\fP section is terminated
with an \s-1ASCII NUL\s+1 character.
.PP
The \fIBoolean flags\fP 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.
.PP
Between the \fIBoolean flags\fP section and the \fInumber\fP section,
a null byte will be inserted,
if necessary,
to ensure that the \fInumber\fP 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.
.PP
The \fInumbers\fP section is similar to the \fIBoolean flags\fP section.
Each capability takes up two bytes,
and is stored as a little-endian short integer.
.PP
The \fIstrings\fP section is also similar.
Each capability is stored as a short integer.
The capability value is an index into the \fIstring table\fP.
.PP
The \fIstring table\fP is the last section.
It contains all of the values of string capabilities referenced in
the \fIstrings\fP section.
Each string is null-terminated.
Special characters in \*^X or \ec notation are stored in their
interpreted form,
not the printing representation.
Padding information
.BI $< nn >
and parameter information
.B %x
are stored intact in uninterpreted form.
.SS "Extended Storage Format"
The previous section describes the conventional
.I \%term\%info
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 standard set of Boolean,
numeric,
or string capabilities.
.PP
The
.I \%ncurses
libraries and applications support extended
.I \%term\%info
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
.I \%term\%info
data when they reach the end of the size given in the header.
.I \%ncurses
checks the size,
and if it exceeds that specified in the header,
continues to parse according to its own scheme.
.PP
First,
it reads the extended header
(5 short integers):
.RS 5
.TP 5
(1)
count of extended Boolean capabilities
.TP 5
(2)
count of extended numeric capabilities
.TP 5
(3)
count of extended string capabilities
.TP 5
(4)
count of the items in extended string table
.TP 5
(5)
size of the extended string table in bytes
.RE
.PP
The count- and size-values for the extended string table
include the extended capability \fInames\fP as well as
extended capability \fIvalues\fP.
.PP
Using the counts and sizes,
.I \%ncurses
allocates arrays and reads data for the extended capabilities in the
same order as the header information.
.PP
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.
.PP
By storing terminal descriptions in this way,
.I \%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 \fB\%user_caps\fP(5) for an overview of the way
.I \%ncurses
uses this extended information.
.PP
Applications that manipulate terminal data can use the definitions
described in \fB\%term_variables\fP(3X) associating the long capability
names with members of a
.I \%TERMTYPE
structure.
.
.SS "Extended Number Format"
On occasion,
16-bit signed integers are not large enough.
.I \%ncurses
6.1 introduced a new format
by making a few changes to the legacy format:
.bP
a different magic number
(octal 01036)
.bP
changing the type for the \fInumber\fP array from signed 16-bit integers
to signed 32-bit integers.
.PP
To maintain compatibility,
the library presents the same data structures
to direct users of the
.I \%TERMTYPE
structure as in previous formats.
However,
that cannot provide callers with the extended numbers.
The library uses a similar but hidden data structure
.I \%TERMTYPE2
to provide data for the
.I \%term\%info
functions.
.SH FILES
.TP
.I @TERMINFO@
compiled terminal description database
.SH PORTABILITY
.SS setupterm
Note that it is possible for
.B setupterm
to expect a different set of capabilities
than are actually present in the file.
Either the database may have been updated since
.B 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
.B 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.
.SS "Binary Format"
X/Open Curses does not specify a format for the
.I \%term\%info
database.
System\ V
.I curses
used a directory-tree of binary files,
one per terminal description.
.PP
Despite the consistent use of little-endian numbers and the otherwise
self-describing format,
it is not wise to count on portability of binary
.I \%term\%info
entries between commercial Unix versions.
The problem is that there are at least three versions of
.I \%term\%info
(under HP\-UX,
AIX,
and OSF/1)
each of which diverged from System\ V
.I \%term\%info
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 \fB\%terminfo\fP(5) for detailed
discussion of
.I \%term\%info
source compatibility issues.
.PP
This implementation is by default compatible with the binary
.I \%term\%info
format used by Solaris
.IR 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
.I \%ncurses
with different configuration options.
.SS "Magic Codes"
The magic number in a binary
.I \%term\%info
file is the first 16 bits
(two bytes).
Besides making it more reliable for the library to check that a file is
.IR \%term\%info ,
utilities such as \fIfile\fP(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 \fB\%scr_dump\fP(5)).
This implementation uses 01036 as a continuation of that sequence,
but with a different high-order byte to avoid confusion.
.SS "The \fITERMTYPE\fP Structure"
Direct access to the
.I \%TERMTYPE
structure is provided for legacy applications.
Portable applications should use \fB\%tigetflag\fP(3X) and related
functions to read terminal capabilities.
.SS "Mixed-case Terminal Names"
A small number of terminal descriptions use uppercase characters in
their names.
If the underlying file system ignores the difference between
uppercase and lowercase,
.I \%ncurses
represents the \*(``first character\*('' of the terminal name used as
the intermediate level of a directory tree in (two-character)
hexadecimal form.
.SS Limits
.I \%ncurses
stores compiled terminal descriptions in three related formats,
described in the subsections
.bP
.BR "Legacy Storage Format" ,
and
.bP
.BR "Extended Storage Format" ,
and
.bP
.BR "Extended Number Format" .
.PP
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
.I \%ncurses
5.0 adds data to either of these formats.
.PP
Some limitations apply:
.bP
total compiled entries cannot exceed 4096 bytes in the legacy format.
.bP
total compiled entries cannot exceed 32768 bytes in the extended format.
.bP
the name field cannot exceed 128 bytes.
.PP
Compiled entries are limited to 32768 bytes because offsets into the
\fIstrings table\fP use two-byte integers.
The legacy format could have supported 32768-byte entries,
but was limited to a virtual memory page's 4096 bytes.
.SH EXAMPLES
Here is a
.I \%term\%info
description of the Lear-Siegler ADM-3,
a popular though rather stupid early terminal.
.PP
.EX
.nf
adm3a|lsi adm3a,
am,
cols#80, lines#24,
bel=\*^G, clear=\e032$<1>, cr=\*^M, cub1=\*^H, cud1=\*^J,
cuf1=\*^L, cup=\eE=%p1%{32}%+%c%p2%{32}%+%c, cuu1=\*^K,
home=\*^\*^, ind=\*^J,
.fi
.EE
.PP
A hexadecimal dump of its compiled terminal description
(in legacy format)
follows.
.PP
.if t .in +4n
.ft \*(CW
.TS
Lp-1.
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 ........ .
.TE
.ft
.in
.SH AUTHORS
Thomas E. Dickey
.br
extended
.I \%term\%info
format for
.I \%ncurses
5.0
.br
hashed database support for
.I \%ncurses
5.6
.br
extended number support for
.I \%ncurses
6.1
.sp
Eric S. Raymond
.br
documented legacy
.I \%term\%info
format
(that used by
.IR \%pcurses ).
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_terminfo\fP(3X),
\fB\%terminfo\fP(5),
\fB\%user_caps\fP(5)
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