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This is Info file /home/gd/gnu/termcap/termcap.info, produced by
Makeinfo-1.52 from the input file /home/gd/gnu/termcap/termcap.texi.
This file documents the termcap library of the GNU system.
Copyright (C) 1988 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.

File: termcap.info, Node: Naming, Next: Inheriting, Prev: Capability Format, Up: Data Base
Terminal Type Name Conventions
==============================
There are conventions for choosing names of terminal types. For one
thing, all letters should be in lower case. The terminal type for a
terminal in its most usual or most fundamental mode of operation should
not have a hyphen in it.
If the same terminal has other modes of operation which require
different terminal descriptions, these variant descriptions are given
names made by adding suffixes with hyphens. Such alternate descriptions
are used for two reasons:
* When the terminal has a switch that changes its behavior. Since
the computer cannot tell how the switch is set, the user must tell
the computer by choosing the appropriate terminal type name.
For example, the VT-100 has a setup flag that controls whether the
cursor wraps at the right margin. If this flag is set to "wrap",
you must use the terminal type `vt100-am'. Otherwise you must use
`vt100-nam'. Plain `vt100' is defined as a synonym for either
`vt100-am' or `vt100-nam' depending on the preferences of the
local site.
The standard suffix `-am' stands for "automatic margins".
* To give the user a choice in how to use the terminal. This is done
when the terminal has a switch that the computer normally controls.
For example, the Ann Arbor Ambassador can be configured with many
screen sizes ranging from 20 to 60 lines. Fewer lines make bigger
characters but more lines let you see more of what you are editing.
As a result, users have different preferences. Therefore, termcap
provides terminal types for many screen sizes. If you choose type
`aaa-30', the terminal will be configured to use 30 lines; if you
choose `aaa-48', 48 lines will be used, and so on.
Here is a list of standard suffixes and their conventional meanings:
`-w'
Short for "wide". This is a mode that gives the terminal more
columns than usual. This is normally a user option.
`-am'
"Automatic margins". This is an alternate description for use when
the terminal's margin-wrap switch is on; it contains the `am'
flag. The implication is that normally the switch is off and the
usual description for the terminal says that the switch is off.
`-nam'
"No automatic margins". The opposite of `-am', this names an
alternative description which lacks the `am' flag. This implies
that the terminal is normally operated with the margin-wrap switch
turned on, and the normal description of the terminal says so.
`-na'
"No arrows". This terminal description initializes the terminal to
keep its arrow keys in local mode. This is a user option.
`-rv'
"Reverse video". This terminal description causes text output for
normal video to appear as reverse, and text output for reverse
video to come out as normal. Often this description differs from
the usual one by interchanging the two strings which turn reverse
video on and off.
This is a user option; you can choose either the "reverse video"
variant terminal type or the normal terminal type, and termcap will
obey.
`-s'
"Status". Says to enable use of a status line which ordinary
output does not touch (*note Status Line::.).
Some terminals have a special line that is used only as a status
line. For these terminals, there is no need for an `-s' variant;
the status line commands should be defined by default. On other
terminals, enabling a status line means removing one screen line
from ordinary use and reducing the effective screen height. For
these terminals, the user can choose the `-s' variant type to
request use of a status line.
`-NLINES'
Says to operate with NLINES lines on the screen, for terminals
such as the Ambassador which provide this as an option. Normally
this is a user option; by choosing the terminal type, you control
how many lines termcap will use.
`-NPAGESp'
Says that the terminal has NPAGES pages worth of screen memory,
for terminals where this is a hardware option.
`-unk'
Says that description is not for direct use, but only for
reference in `tc' capabilities. Such a description is a kind of
subroutine, because it describes the common characteristics of
several variant descriptions that would use other suffixes in
place of `-unk'.

File: termcap.info, Node: Inheriting, Next: Changing, Prev: Naming, Up: Data Base
Inheriting from Related Descriptions
====================================
When two terminal descriptions are similar, their identical parts do
not need to be given twice. Instead, one of the two can be defined in
terms of the other, using the `tc' capability. We say that one
description "refers to" the other, or "inherits from" the other.
The `tc' capability must be the last one in the terminal description,
and its value is a string which is the name of another terminal type
which is referred to. For example,
N9|aaa|ambassador|aaa-30|ann arbor ambassador/30 lines:\
:ti=\E[2J\E[30;0;0;30p:\
:te=\E[60;0;0;30p\E[30;1H\E[J:\
:li#30:tc=aaa-unk:
defines the terminal type `aaa-30' (also known as plain `aaa') in terms
of `aaa-unk', which defines everything about the Ambassador that is
independent of screen height. The types `aaa-36', `aaa-48' and so on
for other screen heights are likewise defined to inherit from `aaa-unk'.
The capabilities overridden by `aaa-30' include `li', which says how
many lines there are, and `ti' and `te', which configure the terminal
to use that many lines.
The effective terminal description for type `aaa' consists of the
text shown above followed by the text of the description of `aaa-unk'.
The `tc' capability is handled automatically by `tgetent', which finds
the description thus referenced and combines the two descriptions
(*note Find::.). Therefore, only the implementor of the terminal
descriptions needs to think about using `tc'. Users and application
programmers do not need to be concerned with it.
Since the reference terminal description is used last, capabilities
specified in the referring description override any specifications of
the same capabilities in the reference description.
The referring description can cancel out a capability without
specifying any new value for it by means of a special trick. Write the
capability in the referring description, with the character `@' after
the capability name, as follows:
NZ|aaa-30-nam|ann arbor ambassador/30 lines/no automatic-margins:\
:am@:tc=aaa-30:

File: termcap.info, Node: Changing, Prev: Inheriting, Up: Data Base
When Changes in the Data Base Take Effect
=========================================
Each application program must read the terminal description from the
data base, so a change in the data base is effective for all jobs
started after the change is made.
The change will usually have no effect on a job that have been in
existence since before the change. The program probably read the
terminal description once, when it was started, and is continuing to
use what it read then. If the program does not have a feature for
reexamining the data base, then you will need to run it again (probably
killing the old job).
If the description in use is coming from the `TERMCAP' environment
variable, then the data base file is effectively overridden, and
changes in it will have no effect until you change the `TERMCAP'
variable as well. For example, some users' `.login' files
automatically copy the terminal description into `TERMCAP' to speed
startup of applications. If you have done this, you will need to
change the `TERMCAP' variable to make the changed data base take effect.

File: termcap.info, Node: Capabilities, Next: Summary, Prev: Data Base, Up: Top
Definitions of the Terminal Capabilities
****************************************
This section is divided into many subsections, each for one aspect of
use of display terminals. For writing a display program, you usually
need only check the subsections for the operations you want to use.
For writing a terminal description, you must read each subsection and
fill in the capabilities described there.
String capabilities that are display commands may require numeric
parameters (*note Parameters::.). Most such capabilities do not use
parameters. When a capability requires parameters, this is explicitly
stated at the beginning of its definition. In simple cases, the first
or second sentence of the definition mentions all the parameters, in
the order they should be given, using a name in upper case for each
one. For example, the `rp' capability is a command that requires two
parameters; its definition begins as follows:
String of commands to output a graphic character C, repeated N
times.
In complex cases or when there are many parameters, they are
described explicitly.
When a capability is described as obsolete, this means that programs
should not be written to look for it, but terminal descriptions should
still be written to provide it.
When a capability is described as very obsolete, this means that it
should be omitted from terminal descriptions as well.
* Menu:
* Basic:: Basic characteristics.
* Screen Size:: Screen size, and what happens when it changes.
* Cursor Motion:: Various ways to move the cursor.
* Wrapping:: What happens if you write a character in the last column.
* Scrolling:: Pushing text up and down on the screen.
* Windows:: Limiting the part of the window that output affects.
* Clearing:: Erasing one or many lines.
* Insdel Line:: Making new blank lines in mid-screen; deleting lines.
* Insdel Char:: Inserting and deleting characters within a line.
* Standout:: Highlighting some of the text.
* Underlining:: Underlining some of the text.
* Cursor Visibility:: Making the cursor more or less easy to spot.
* Bell:: Attracts user's attention; not localized on the screen.
* Keypad:: Recognizing when function keys or arrows are typed.
* Meta Key:: META acts like an extra shift key.
* Initialization:: Commands used to initialize or reset the terminal.
* Pad Specs:: Info for the kernel on how much padding is needed.
* Status Line:: A status line displays "background" information.
* Half-Line:: Moving by half-lines, for superscripts and subscripts.
* Printer:: Controlling auxiliary printers of display terminals.

File: termcap.info, Node: Basic, Next: Screen Size, Up: Capabilities
Basic Characteristics
=====================
This section documents the capabilities that describe the basic and
nature of the terminal, and also those that are relevant to the output
of graphic characters.
`os'
Flag whose presence means that the terminal can overstrike. This
means that outputting a graphic character does not erase whatever
was present in the same character position before. The terminals
that can overstrike include printing terminals, storage tubes (all
obsolete nowadays), and many bit-map displays.
`eo'
Flag whose presence means that outputting a space erases a
character position even if the terminal supports overstriking. If
this flag is not present and overstriking is supported, output of
a space has no effect except to move the cursor.
(On terminals that do not support overstriking, you can always
assume that outputting a space at a position erases whatever
character was previously displayed there.)
`gn'
Flag whose presence means that this terminal type is a generic type
which does not really describe any particular terminal. Generic
types are intended for use as the default type assigned when the
user connects to the system, with the intention that the user
should specify what type he really has. One example of a generic
type is the type `network'.
Since the generic type cannot say how to do anything interesting
with the terminal, termcap-using programs will always find that the
terminal is too weak to be supported if the user has failed to
specify a real terminal type in place of the generic one. The
`gn' flag directs these programs to use a different error message:
"You have not specified your real terminal type", rather than
"Your terminal is not powerful enough to be used".
`hc'
Flag whose presence means this is a hardcopy terminal.
`rp'
String of commands to output a graphic character C, repeated N
times. The first parameter value is the ASCII code for the desired
character, and the second parameter is the number of times to
repeat the character. Often this command requires padding
proportional to the number of times the character is repeated.
This effect can be had by using parameter arithmetic with
`%'-sequences to compute the amount of padding, then generating
the result as a number at the front of the string so that `tputs'
will treat it as padding.
`hz'
Flag whose presence means that the ASCII character `~' cannot be
output on this terminal because it is used for display commands.
Programs handle this flag by checking all text to be output and
replacing each `~' with some other character(s). If this is not
done, the screen will be thoroughly garbled.
The old Hazeltine terminals that required such treatment are
probably very rare today, so you might as well not bother to
support this flag.
`CC'
String whose presence means the terminal has a settable command
character. The value of the string is the default command
character (which is usually ESC).
All the strings of commands in the terminal description should be
written to use the default command character. If you are writing
an application program that changes the command character, use the
`CC' capability to figure out how to translate all the display
commands to work with the new command character.
Most programs have no reason to look at the `CC' capability.
`xb'
Flag whose presence identifies Superbee terminals which are unable
to transmit the characters ESC and `Control-C'. Programs which
support this flag are supposed to check the input for the code
sequences sent by the F1 and F2 keys, and pretend that ESC or
`Control-C' (respectively) had been read. But this flag is
obsolete, and not worth supporting.

File: termcap.info, Node: Screen Size, Next: Cursor Motion, Prev: Basic, Up: Capabilities
Screen Size
===========
A terminal description has two capabilities, `co' and `li', that
describe the screen size in columns and lines. But there is more to
the question of screen size than this.
On some operating systems the "screen" is really a window and the
effective width can vary. On some of these systems, `tgetnum' uses the
actual width of the window to decide what value to return for the `co'
capability, overriding what is actually written in the terminal
description. On other systems, it is up to the application program to
check the actual window width using a system call. For example, on BSD
4.3 systems, the system call `ioctl' with code `TIOCGWINSZ' will tell
you the current screen size.
On all window systems, termcap is powerless to advise the application
program if the user resizes the window. Application programs must deal
with this possibility in a system-dependent fashion. On some systems
the C shell handles part of the problem by detecting changes in window
size and setting the `TERMCAP' environment variable appropriately.
This takes care of application programs that are started subsequently.
It does not help application programs already running.
On some systems, including BSD 4.3, all programs using a terminal get
a signal named `SIGWINCH' whenever the screen size changes. Programs
that use termcap should handle this signal by using `ioctl TIOCGWINSZ'
to learn the new screen size.
`co'
Numeric value, the width of the screen in character positions.
Even hardcopy terminals normally have a `co' capability.
`li'
Numeric value, the height of the screen in lines.

File: termcap.info, Node: Cursor Motion, Next: Wrapping, Prev: Screen Size, Up: Capabilities
Cursor Motion
=============
Termcap assumes that the terminal has a "cursor", a spot on the
screen where a visible mark is displayed, and that most display
commands take effect at the position of the cursor. It follows that
moving the cursor to a specified location is very important.
There are many terminal capabilities for different cursor motion
operations. A terminal description should define as many as possible,
but most programs do not need to use most of them. One capability,
`cm', moves the cursor to an arbitrary place on the screen; this by
itself is sufficient for any application as long as there is no need to
support hardcopy terminals or certain old, weak displays that have only
relative motion commands. Use of other cursor motion capabilities is an
optimization, enabling the program to output fewer characters in some
common cases.
If you plan to use the relative cursor motion commands in an
application program, you must know what the starting cursor position
is. To do this, you must keep track of the cursor position and update
the records each time anything is output to the terminal, including
graphic characters. In addition, it is necessary to know whether the
terminal wraps after writing in the rightmost column. *Note Wrapping::.
One other motion capability needs special mention: `nw' moves the
cursor to the beginning of the following line, perhaps clearing all the
starting line after the cursor, or perhaps not clearing at all. This
capability is a least common denominator that is probably supported
even by terminals that cannot do most other things such as `cm' or `do'.
Even hardcopy terminals can support `nw'.
`cm'
String of commands to position the cursor at line L, column C.
Both parameters are origin-zero, and are defined relative to the
screen, not relative to display memory.
All display terminals except a few very obsolete ones support `cm',
so it is acceptable for an application program to refuse to
operate on terminals lacking `cm'.
`ho'
String of commands to move the cursor to the upper left corner of
the screen (this position is called the "home position"). In
terminals where the upper left corner of the screen is not the
same as the beginning of display memory, this command must go to
the upper left corner of the screen, not the beginning of display
memory.
Every display terminal supports this capability, and many
application programs refuse to operate if the `ho' capability is
missing.
`ll'
String of commands to move the cursor to the lower left corner of
the screen. On some terminals, moving up from home position does
this, but programs should never assume that will work. Just
output the `ll' string (if it is provided); if moving to home
position and then moving up is the best way to get there, the `ll'
command will do that.
`cr'
String of commands to move the cursor to the beginning of the line
it is on. If this capability is not specified, many programs
assume they can use the ASCII carriage return character for this.
`le'
String of commands to move the cursor left one column. Unless the
`bw' flag capability is specified, the effect is undefined if the
cursor is at the left margin; do not use this command there. If
`bw' is present, this command may be used at the left margin, and
it wraps the cursor to the last column of the preceding line.
`nd'
String of commands to move the cursor right one column. The
effect is undefined if the cursor is at the right margin; do not
use this command there, not even if `am' is present.
`up'
String of commands to move the cursor vertically up one line. The
effect of sending this string when on the top line is undefined;
programs should never use it that way.
`do'
String of commands to move the cursor vertically down one line.
The effect of sending this string when on the bottom line is
undefined; programs should never use it that way.
Some programs do use `do' to scroll up one line if used at the
bottom line, if `sf' is not defined but `sr' is. This is only to
compensate for certain old, incorrect terminal descriptions. (In
principle this might actually lead to incorrect behavior on other
terminals, but that seems to happen rarely if ever.) But the
proper solution is that the terminal description should define
`sf' as well as `do' if the command is suitable for scrolling.
The original idea was that this string would not contain a newline
character and therefore could be used without disabling the
kernel's usual habit of converting of newline into a
carriage-return newline sequence. But many terminal descriptions
do use newline in the `do' string, so this is not possible; a
program which sends the `do' string must disable output conversion
in the kernel (*note Initialize::.).
`bw'
Flag whose presence says that `le' may be used in column zero to
move to the last column of the preceding line. If this flag is
not present, `le' should not be used in column zero.
`nw'
String of commands to move the cursor to start of next line,
possibly clearing rest of line (following the cursor) before
moving.
`DO', `UP', `LE', `RI'
Strings of commands to move the cursor N lines down vertically, up
vertically, or N columns left or right. Do not attempt to move
past any edge of the screen with these commands; the effect of
trying that is undefined. Only a few terminal descriptions provide
these commands, and most programs do not use them.
`CM'
String of commands to position the cursor at line L, column C,
relative to display memory. Both parameters are origin-zero.
This capability is present only in terminals where there is a
difference between screen-relative and memory-relative addressing,
and not even in all such terminals.
`ch'
String of commands to position the cursor at column C in the same
line it is on. This is a special case of `cm' in which the
vertical position is not changed. The `ch' capability is provided
only when it is faster to output than `cm' would be in this
special case. Programs should not assume most display terminals
have `ch'.
`cv'
String of commands to position the cursor at line L in the same
column. This is a special case of `cm' in which the horizontal
position is not changed. The `cv' capability is provided only
when it is faster to output than `cm' would be in this special
case. Programs should not assume most display terminals have `cv'.
`sc'
String of commands to make the terminal save the current cursor
position. Only the last saved position can be used. If this
capability is present, `rc' should be provided also. Most
terminals have neither.
`rc'
String of commands to make the terminal restore the last saved
cursor position. If this capability is present, `sc' should be
provided also. Most terminals have neither.
`ff'
String of commands to advance to the next page, for a hardcopy
terminal.
`ta'
String of commands to move the cursor right to the next hardware
tab stop column. Missing if the terminal does not have any kind of
hardware tabs. Do not send this command if the kernel's terminal
modes say that the kernel is expanding tabs into spaces.
`bt'
String of commands to move the cursor left to the previous hardware
tab stop column. Missing if the terminal has no such ability; many
terminals do not. Do not send this command if the kernel's
terminal modes say that the kernel is expanding tabs into spaces.
The following obsolete capabilities should be included in terminal
descriptions when appropriate, but should not be looked at by new
programs.
`nc'
Flag whose presence means the terminal does not support the ASCII
carriage return character as `cr'. This flag is needed because
old programs assume, when the `cr' capability is missing, that
ASCII carriage return can be used for the purpose. We use `nc' to
tell the old programs that carriage return may not be used.
New programs should not assume any default for `cr', so they need
not look at `nc'. However, descriptions should contain `nc'
whenever they do not contain `cr'.
`xt'
Flag whose presence means that the ASCII tab character may not be
used for cursor motion. This flag exists because old programs
assume, when the `ta' capability is missing, that ASCII tab can be
used for the purpose. We use `xt' to tell the old programs not to
use tab.
New programs should not assume any default for `ta', so they need
not look at `xt' in connection with cursor motion. Note that `xt'
also has implications for standout mode (*note Standout::.). It
is obsolete in regard to cursor motion but not in regard to
standout.
In fact, `xt' means that the terminal is a Teleray 1061.
`bc'
Very obsolete alternative name for the `le' capability.
`bs'
Flag whose presence means that the ASCII character backspace may be
used to move the cursor left. Obsolete; look at `le' instead.
`nl'
Obsolete capability which is a string that can either be used to
move the cursor down or to scroll. The same string must scroll
when used on the bottom line and move the cursor when used on any
other line. New programs should use `do' or `sf', and ignore `nl'.
If there is no `nl' capability, some old programs assume they can
use the newline character for this purpose. These programs follow
a bad practice, but because they exist, it is still desirable to
define the `nl' capability in a terminal description if the best
way to move down is *not* a newline.

File: termcap.info, Node: Wrapping, Next: Scrolling, Prev: Cursor Motion, Up: Capabilities
Wrapping
========
"Wrapping" means moving the cursor from the right margin to the left
margin of the following line. Some terminals wrap automatically when a
graphic character is output in the last column, while others do not.
Most application programs that use termcap need to know whether the
terminal wraps. There are two special flag capabilities to describe
what the terminal does when a graphic character is output in the last
column.
`am'
Flag whose presence means that writing a character in the last
column causes the cursor to wrap to the beginning of the next line.
If `am' is not present, writing in the last column leaves the
cursor at the place where the character was written.
Writing in the last column of the last line should be avoided on
terminals with `am', as it may or may not cause scrolling to occur
(*note Scrolling::.). Scrolling is surely not what you would
intend.
If your program needs to check the `am' flag, then it also needs
to check the `xn' flag which indicates that wrapping happens in a
strange way. Many common terminals have the `xn' flag.
`xn'
Flag whose presence means that the cursor wraps in a strange way.
At least two distinct kinds of strange behavior are known; the
termcap data base does not contain anything to distinguish the two.
On Concept-100 terminals, output in the last column wraps the
cursor almost like an ordinary `am' terminal. But if the next
thing output is a newline, it is ignored.
DEC VT-100 terminals (when the wrap switch is on) do a different
strange thing: the cursor wraps only if the next thing output is
another graphic character. In fact, the wrap occurs when the
following graphic character is received by the terminal, before the
character is placed on the screen.
On both of these terminals, after writing in the last column a
following graphic character will be displayed in the first column
of the following line. But the effect of relative cursor motion
characters such as newline or backspace at such a time depends on
the terminal. The effect of erase or scrolling commands also
depends on the terminal. You can't assume anything about what
they will do on a terminal that has `xn'. So, to be safe, you
should never do these things at such a time on such a terminal.
To be sure of reliable results on a terminal which has the `xn'
flag, output a `cm' absolute positioning command after writing in
the last column. Another safe thing to do is to output
carriage-return newline, which will leave the cursor at the
beginning of the following line.

File: termcap.info, Node: Scrolling, Next: Windows, Prev: Wrapping, Up: Capabilities
Scrolling
=========
"Scrolling" means moving the contents of the screen up or down one or
more lines. Moving the contents up is "forward scrolling"; moving them
down is "reverse scrolling".
Scrolling happens after each line of output during ordinary output
on most display terminals. But in an application program that uses
termcap for random-access output, scrolling happens only when
explicitly requested with the commands in this section.
Some terminals have a "scroll region" feature. This lets you limit
the effect of scrolling to a specified range of lines. Lines outside
the range are unaffected when scrolling happens. The scroll region
feature is available if either `cs' or `cS' is present.
`sf'
String of commands to scroll the screen one line up, assuming it is
output with the cursor at the beginning of the bottom line.
`sr'
String of commands to scroll the screen one line down, assuming it
is output with the cursor at the beginning of the top line.
`do'
A few programs will try to use `do' to do the work of `sf'. This
is not really correct--it is an attempt to compensate for the
absence of a `sf' command in some old terminal descriptions.
Since these terminal descriptions do define `sr', perhaps at one
time the definition of `do' was different and it could be used for
scrolling as well. But it isn't desirable to combine these two
functions in one capability, since scrolling often requires more
padding than simply moving the cursor down. Defining `sf' and
`do' separately allows you to specify the padding properly. Also,
all sources agree that `do' should not be relied on to do
scrolling.
So the best approach is to add `sf' capabilities to the
descriptions of these terminals, copying the definition of `do' if
that does scroll.
`SF'
String of commands to scroll the screen N lines up, assuming it is
output with the cursor at the beginning of the bottom line.
`SR'
String of commands to scroll the screen N lines down, assuming it
is output with the cursor at the beginning of the top line.
`cs'
String of commands to set the scroll region. This command takes
two parameters, START and END, which are the line numbers
(origin-zero) of the first line to include in the scroll region
and of the last line to include in it. When a scroll region is
set, scrolling is limited to the specified range of lines; lines
outside the range are not affected by scroll commands.
Do not try to move the cursor outside the scroll region. The
region remains set until explicitly removed. To remove the scroll
region, use another `cs' command specifying the full height of the
screen.
The cursor position is undefined after the `cs' command is set, so
position the cursor with `cm' immediately afterward.
`cS'
String of commands to set the scroll region using parameters in
different form. The effect is the same as if `cs' were used.
Four parameters are required:
1. Total number of lines on the screen.
2. Number of lines above desired scroll region.
3. Number of lines below (outside of) desired scroll region.
4. Total number of lines on the screen, the same as the first
parameter.
This capability is a GNU extension that was invented to allow the
Ann Arbor Ambassador's scroll-region command to be described; it
could also be done by putting non-Unix `%'-sequences into a `cs'
string, but that would have confused Unix programs that used the
`cs' capability with the Unix termcap. Currently only GNU Emacs
uses the `cS' capability.
`ns'
Flag which means that the terminal does not normally scroll for
ordinary sequential output. For modern terminals, this means that
outputting a newline in ordinary sequential output with the cursor
on the bottom line wraps to the top line. For some obsolete
terminals, other things may happen.
The terminal may be able to scroll even if it does not normally do
so. If the `sf' capability is provided, it can be used for
scrolling regardless of `ns'.
`da'
Flag whose presence means that lines scrolled up off the top of the
screen may come back if scrolling down is done subsequently.
The `da' and `db' flags do not, strictly speaking, affect how to
scroll. But programs that scroll usually need to clear the lines
scrolled onto the screen, if these flags are present.
`db'
Flag whose presence means that lines scrolled down off the bottom
of the screen may come back if scrolling up is done subsequently.
`lm'
Numeric value, the number of lines of display memory that the
terminal has. A value of zero means that the terminal has more
display memory than can fit on the screen, but no fixed number of
lines. (The number of lines may depend on the amount of text in
each line.)
Any terminal description that defines `SF' should also define `sf';
likewise for `SR' and `sr'. However, many terminals can only scroll by
one line at a time, so it is common to find `sf' and not `SF', or `sr'
without `SR'.
Therefore, all programs that use the scrolling facilities should be
prepared to work with `sf' in the case that `SF' is absent, and
likewise with `sr'. On the other hand, an application program that
uses only `sf' and not `SF' is acceptable, though slow on some
terminals.
When outputting a scroll command with `tputs', the NLINES argument
should be the total number of lines in the portion of the screen being
scrolled. Very often these commands require padding proportional to
this number of lines. *Note Padding::.

File: termcap.info, Node: Windows, Next: Clearing, Prev: Scrolling, Up: Capabilities
Windows
=======
A "window", in termcap, is a rectangular portion of the screen to
which all display operations are restricted. Wrapping, clearing,
scrolling, insertion and deletion all operate as if the specified
window were all the screen there was.
`wi'
String of commands to set the terminal output screen window. This
string requires four parameters, all origin-zero:
1. The first line to include in the window.
2. The last line to include in the window.
3. The first column to include in the window.
4. The last column to include in the window.
Most terminals do not support windows.

File: termcap.info, Node: Clearing, Next: Insdel Line, Prev: Windows, Up: Capabilities
Clearing Parts of the Screen
============================
There are several terminal capabilities for clearing parts of the
screen to blank. All display terminals support the `cl' string, and
most display terminals support all of these capabilities.
`cl'
String of commands to clear the entire screen and position the
cursor at the upper left corner.
`cd'
String of commands to clear the line the cursor is on, and all the
lines below it, down to the bottom of the screen. This command
string should be used only with the cursor in column zero; their
effect is undefined if the cursor is elsewhere.
`ce'
String of commands to clear from the cursor to the end of the
current line.
`ec'
String of commands to clear N characters, starting with the
character that the cursor is on. This command string is expected
to leave the cursor position unchanged. The parameter N should
never be large enough to reach past the right margin; the effect
of such a large parameter would be undefined.
Clear to end of line (`ce') is extremely important in programs that
maintain an updating display. Nearly all display terminals support this
operation, so it is acceptable for a an application program to refuse to
work if `ce' is not present. However, if you do not want this
limitation, you can accomplish clearing to end of line by outputting
spaces until you reach the right margin. In order to do this, you must
know the current horizontal position. Also, this technique assumes
that writing a space will erase. But this happens to be true on all
the display terminals that fail to support `ce'.

File: termcap.info, Node: Insdel Line, Next: Insdel Char, Prev: Clearing, Up: Capabilities
Insert/Delete Line
==================
"Inserting a line" means creating a blank line in the middle of the
screen, and pushing the existing lines of text apart. In fact, the
lines above the insertion point do not change, while the lines below
move down, and one is normally lost at the bottom of the screen.
"Deleting a line" means causing the line to disappear from the
screen, closing up the gap by moving the lines below it upward. A new
line appears at the bottom of the screen. Usually this line is blank,
but on terminals with the `db' flag it may be a line previously moved
off the screen bottom by scrolling or line insertion.
Insertion and deletion of lines is useful in programs that maintain
an updating display some parts of which may get longer or shorter.
They are also useful in editors for scrolling parts of the screen, and
for redisplaying after lines of text are killed or inserted.
Many terminals provide commands to insert or delete a single line at
the cursor position. Some provide the ability to insert or delete
several lines with one command, using the number of lines to insert or
delete as a parameter. Always move the cursor to column zero before
using any of these commands.
`al'
String of commands to insert a blank line before the line the
cursor is on. The existing line, and all lines below it, are
moved down. The last line in the screen (or in the scroll region,
if one is set) disappears and in most circumstances is discarded.
It may not be discarded if the `db' is present (*note
Scrolling::.).
The cursor must be at the left margin before this command is used.
This command does not move the cursor.
`dl'
String of commands to delete the line the cursor is on. The
following lines move up, and a blank line appears at the bottom of
the screen (or bottom of the scroll region). If the terminal has
the `db' flag, a nonblank line previously pushed off the screen
bottom may reappear at the bottom.
The cursor must be at the left margin before this command is used.
This command does not move the cursor.
`AL'
String of commands to insert N blank lines before the line that
the cursor is on. It is like `al' repeated N times, except that
it is as fast as one `al'.
`DL'
String of commands to delete N lines starting with the line that
the cursor is on. It is like `dl' repeated N times, except that
it is as fast as one `dl'.
Any terminal description that defines `AL' should also define `al';
likewise for `DL' and `dl'. However, many terminals can only insert or
delete one line at a time, so it is common to find `al' and not `AL',
or `dl' without `DL'.
Therefore, all programs that use the insert and delete facilities
should be prepared to work with `al' in the case that `AL' is absent,
and likewise with `dl'. On the other hand, it is acceptable to write
an application that uses only `al' and `dl' and does not look for `AL'
or `DL' at all.
If a terminal does not support line insertion and deletion directly,
but does support a scroll region, the effect of insertion and deletion
can be obtained with scrolling. However, it is up to the individual
user program to check for this possibility and use the scrolling
commands to get the desired result. It is fairly important to implement
this alternate strategy, since it is the only way to get the effect of
line insertion and deletion on the popular VT100 terminal.
Insertion and deletion of lines is affected by the scroll region on
terminals that have a settable scroll region. This is useful when it is
desirable to move any few consecutive lines up or down by a few lines.
*Note Scrolling::.
The line pushed off the bottom of the screen is not lost if the
terminal has the `db' flag capability; instead, it is pushed into
display memory that does not appear on the screen. This is the same
thing that happens when scrolling pushes a line off the bottom of the
screen. Either reverse scrolling or deletion of a line can bring the
apparently lost line back onto the bottom of the screen. If the
terminal has the scroll region feature as well as `db', the pushed-out
line really is lost if a scroll region is in effect.
When outputting an insert or delete command with `tputs', the NLINES
argument should be the total number of lines from the cursor to the
bottom of the screen (or scroll region). Very often these commands
require padding proportional to this number of lines. *Note Padding::.
For `AL' and `DL' the NLINES argument should *not* depend on the
number of lines inserted or deleted; only the total number of lines
affected. This is because it is just as fast to insert two or N lines
with `AL' as to insert one line with `al'.