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[unix-history] / man / termcap.u

.TH TERMCAP UCB 4/8/79 UCB
.SH NAME
termcap \- terminal capability data base
.SH SYNOPSIS
/etc/termcap
.SH DESCRIPTION
.I Termcap
is a data base describing terminals used primarily by
.IR ex (UCB)
and
.IR vi (UCB),
and also by
.IR tset (UCB).
Terminals are described in
.I termcap
by giving a set of capabilities which they have, and by describing
how operations are performed.
Padding requirements and initialization sequences
are included in
.I termcap.
.PP
Entries in
.I termcap
consist of a number of `:' separated fields.
The first entry for each terminal gives the names which are known for the
terminal, separated by `|' characters.  The first name is always 2 characters
long and is used by older version 6 systems which store the terminal type
in a 16 bit word in a systemwide data base.
The second name given is the most common abbreviation for the terminal, and the
last name given should be a long name fully identifying the terminal.
The second name should contain no blanks; the last name may well contain
blanks for readability.
.PP
The following entry, which describes the Concept\-100, is among the more
complex entries in the
.I termcap
file as of this writing.
.PP
.nf
c1|c100|concept100:is=\eEU\eEf\eE7\eE5\eE8\eEl\eENH\eEK\eE\e200\eEo&\e200:\e
        :al=3*\eE^R:am:bs:cd=16*\eE^C:ce=16\eE^S:cl=2*^L:cm=\eEa%+ %+ :co#80:\e
        :dc=16\eE^A:dl=3*\eE^B:ei=\eE\e200:eo:im=\eE^P:in:ip=16*:li#24:mi:nd=\eE=:\e
        :se=\eEd\eEe:so=\eED\eEE:ta=8\et:ul:up=\eE;:vb=\eEk\eEK:xn:
.fi
.PP
Note that entries may continue onto multiple lines by giving a \e as the last
character of a line, and that empty fields
may be included for readability (here between the last field on a line
and the first field on the next).
Capabilities in
.I termcap
are of three types:
Boolean capabilities which indicate that the terminal has
some particular feature, numeric capabilities giving the size of the terminal
or the size of particular delays, and string
capabilities, which give a sequence which can be used to perform particular
terminal operations.
.PP
All capabilities have two letter codes.  For instance, the fact that
the Concept has ``automatic margins'' (i.e. an automatic return and linefeed
when the end of a line is reached) is indicated by the capability \fBam\fR.
Hence the description of the Concept includes \fBam\fR.
Numeric capabilities are followed by the character `#' and then the value.
Thus \fBco\fR which indicates the number of columns the terminal has
gives the value `80' for the Concept.
.PP
Finally, string valued capabilities, such as \fBce\fR (clear to end of line
sequence) are given by the two character code, an `=', and then a string
ending at the next following `:'.  A delay in milliseconds may appear after
the `=' in such a capability, and padding characters are supplied by the
editor after the remainder of the string is sent to provide this delay.
The delay can be either a integer, e.g. `20', or an integer followed by
an `*', i.e. `3*'.  A `*' indicates that the padding required is proportional
to the number of lines affected by the operation, and the amount given is
the per-affected-unit padding required.
When a `*' is specified, it is sometimes useful to give a delay of the form
`3.5' specify a delay per unit to tenths of milliseconds.
.PP
A number of escape sequences are provided in the string valued capabilities
for easy encoding of characters there.  A \fB\eE\fR maps to an \s-2ESCAPE\s0
character, \fB^x\fR maps to a control-x, and the sequences
\fB\en \er \et \eb \ef\fR give a newline, return, tab, backspace and formfeed.
Finally, characters may be given as three octal digits after a \fB\e\fR,
and the characters \fB^\fR and \fB\fR may be given as \fB\e^\fR and \fB\e\e\fR.
If it is necessary to place a \fB:\fR in a capability it must be escaped in
octal as \fB\e072\fR.
If it is necessary to place a null character in a string capability it
must be encoded as \fB\e200\fR.  The routines which deal with
.I termcap
use C strings, and strip the high bits of the output very late so that
a \fB\e200\fR comes out as a \fB\e000\fR would.
.PP
We now outline how to prepare descriptions of terminals.
The most effective way to prepare a terminal description is by imitating
the description of a similar terminal in
.I termcap
and to build up a description gradually, using partial descriptions
with
.I ex
to check that they are correct.
Be aware that a very unusual terminal may expose deficiencies in
the ability of the
.I termcap
file to describe it
or bugs in
.I ex.
To easily test a new terminal description you can set the environment variable
TERMCAP to a pathname of a file containing the description you are working
on and the editor will look there rather than in
.I /etc/termcap.
(This only works on version 7 systems.)
.PP
.B Basic capabilities
.PP
The number of columns on each line for the terminal is given by the
\fBco\fR numeric capability.  If the terminal is a \s-2CRT\s0, then the
number of lines on the screen is given by the \fBli\fR capability.
If the terminal wraps around to the beginning of the next line when
it reaches the right margin, then it should have the \fBam\fR capability.
If the terminal can clear its screen, then this is given by the
\fBcl\fR string capability.  If the terminal can backspace, then it
should have the \fBbs\fR capability, unless a backspace is accomplished
by a character other than \fB^H\fR (ugh) in which case you should give
this character as the \fBbc\fR string capability.  If it overstrikes
(rather than clearing a position when a character is struck over)
then it should have the \fBos\fR capability.
.PP
A very important point here is that the local cursor motions encoded
in
.I termcap
are undefined at the left and top edges of a \s-2CRT\s0 terminal.
The editor will never attempt to backspace around the left edge, nor
will it attempt to go up locally off the top.  The editor assumes that
feeding off the bottom of the screen will cause the screen to scroll up,
and the \fBam\fR capability tells whether the cursor sticks at the right
edge of the screen.  If the terminal has switch selectable automatic margins,
the
.I termcap
file always assumes that this is on, i.e. \fBam\fR.
.PP
These capabilities suffice to describe hardcopy and ``glass-tty'' terminals.
Thus the model 33 teletype is described as
.PP
.DT
	t3|33|tty33:co#72:os
.PP
while the Lear Siegler \s-2ADM\-3\s0 is described as
.PP
.DT
	cl|adm3|3|lsi adm3:am:bs:cl=^Z:li#24:co#80
.PP
.B Cursor addressing
.PP
Cursor addressing in the terminal is described by a
\fBcm\fR string capability, with 
.IR printf (3s)
like escapes \fB%x\fR in it.
These substitute to encodings of the current line or column position,
while other characters are passed through unchanged.
If the \fBcm\fR string is thought of as being a function, then its
arguments are the line and then the column to which motion is desired,
and the \fB%\fR encodings have the following meanings:
.PP
.DT
.nf
	%d	as in \fIprintf\fR, 0 origin
	%2	like %2d
	%3	like %3d
	%.	like %c
	%+x	adds \fIx\fR to value, then %.
	%<xy	if value < x adds y; then in any case %.
	%r	reverses order of line and column, no output
	%i	increments line/column (for 1 origin)
	%%	gives a single %
	%n	exclusive or row and column with 0140 (DM2500)
.fi
.PP
Consider the HP2645, which, to get to row 3 and column 12, needs
to be sent \eE&a12c03Y padded for 6 milliseconds.  Note that the order
of the rows and columns is inverted here, and that the row and column
are printed as two digits.  Thus its \fBcm\fR capability is ``cm=6\eE&%r%2c%2Y''.
The Microterm \s-2ACT-IV\s0 needs the current row and column sent
preceded by a \fB^T\fR, with the row and column simply encoded in binary,
``cm=^T%.%.''.  Terminals which use ``%.'' need to be able to
backspace the cursor (\fBbs\fR or \fBbc\fR),
and to move the cursor up one line on the screen (\fBup\fR introduced below).
This is necessary because it is not always safe to transmit \fB\et\fR, \fB\en\fR
\fB^D\fR and \fB\er\fR, as the system may change or discard them.
.PP
A final example is the \s-2LSI ADM-3a\s0, which uses row and column
offset by a blank character, thus ``cm=\eE=%+ %+ ''.
.PP
.B Cursor motions
.PP
If the terminal can move the cursor one position to the right, leaving
the character at the current position unchanged, then this sequence should
be given as \fBnd\fR (non-destructive space).  If it can move the cursor
up a line
on the screen in the same column, this should be given as \fBup\fR.
If the terminal has no cursor addressing capability, but can home the cursor
cursor (to very upper left corner of screen) then this can be given as
\fBho\fR; similarly a fast way of getting to the lower left hand corner
can be given as \fBll\fR; this may involve going up with \fBup\fR
from the home position,
but the editor will never do this itself (unless \fBll\fR does) because it
makes no assumption about the effect of moving up from the home position.
.PP
.B Area clears
.PP
If the terminal can clear from the current position to the end of the
line, leaving the cursor where it is, this should be given as \fBce\fR.
If the terminal can clear from the current position to the end of the
display, then this should be given as \fBcd\fR.
The editor only uses
\fBcd\fR from the first column of a line.
.PP
.B Insert/delete line
.PP
If the terminal can open a new blank line before the line where the cursor
is, this should be given as \fBal\fR; this is done only from the first
position of a line.  The cursor must then appear on the newly blank line.
If the terminal can delete the line which the cursor is on, then this
should be given as \fBdl\fR; this is done only from the first position on
the line to be deleted.
If the terminal can scroll the screen backwards, then this can be given as
\fBsb\fR, but just \fBal\fR suffices.
If the terminal can retain display memory above then the
\fBda\fR capability should be given; if display memory can be retained
below then \fBdb\fR should be given.  These let the editor understand
that deleting a line on the screen may bring non-blank lines up from below
or that scrolling back with \fBsb\fR may bring down non-blank lines.
.PP
.B Insert/delete character
.PP
There are two basic kinds of intelligent terminals with respect to
insert/delete character which can be described using
.I termcap.
The most common insert/delete character operations affect only the characters
on the current line and shift characters off the end of the line rigidly.
Other terminals, such as the Concept 100 and the Perkin Elmer Owl, make
a distinction between typed and untyped blanks on the screen, shifting
upon an insert or delete only to an untyped blank on the screen which is
either eliminated, or expanded to two untyped blanks.  You can find out
which kind of terminal you have by clearing the screen and then typing
text separated by cursor motions.  Type ``abc\ \ \ \ def'' using local
cursor motions (not spaces) between the ``abc'' and the ``def''.
Then position the cursor before the ``abc'' and put the terminal in insert
mode.  If typing characters causes the rest of the line to shift
rigidly and characters to fall off the end, then your terminal does
not distinguish between blanks and untyped positions.  If the ``abc''
shifts over to the ``def'' which then move together around the end of the
current line and onto the next as you insert, you have the second type of
terminal, and should give the capability \fBin\fR, which stands for
``insert null''.  If your terminal does something different and unusual
then you may have to modify the editor to get it to use the insert
mode your terminal defines.  We have seen no terminals which have an insert
mode not not falling into one of these two classes.
.PP
The editor can handle both terminals which have an insert mode, and terminals
which send a simple sequence to open a blank position on the current line.
Give as \fBim\fR the sequence to get into insert mode, or give it an
empty value if your terminal uses a sequence to insert a blank position.
Give as \fBei\fR the sequence to leave insert mode (give this, with
an empty value also if you gave \fBim\fR so).
Now give as \fBic\fR any sequence needed to be sent just before sending
the character to be inserted.  Most terminals with a true insert mode
will not give \fBic\fR, terminals which send a sequence to open a screen
position should give it here.  (Insert mode is preferable to the sequence
to open a position on the screen if your terminal has both.)
If post insert padding is needed, give this as a number of milliseconds
in \fBip\fR (a string option).  Any other sequence which may need to be
sent after an insert of a single character may also be given in \fBip\fR.
.PP
It is occasionally necessary to move around while in insert mode
to delete characters on the same line (e.g. if there is a tab after
the insertion position).  If your terminal allows motion while in
insert mode you can give the capability \fBmi\fR to speed up inserting
in this case.  Omitting \fBmi\fR will affect only speed.   Some terminals
(notably Datamedia's) must not have \fBmi\fR because of the way their
insert mode works.
.PP
Finally, you can specify delete mode by giving \fBdm\fR and \fBed\fR
to enter and exit delete mode, and \fBdc\fR to delete a single character
while in delete mode.
.PP
.B Highlighting and visible bells
.PP
If your terminal has sequences to enter and exit standout mode these
can be given as \fBso\fR and \fBse\fR respectively.  If the terminal has
a way of flashing the screen to indicate an error quietly (a bell replacement)
then this can be given as \fBvb\fR; it must not move the cursor.
Finally, if the terminal should be placed in a different mode during
open and visual modes of
.I ex,
this can be given as
\fBvs\fR and \fBve\fR, sent at the start and end of these modes
respectively.  These can be used to change, e.g., from a underline
to a block cursor and back.
.PP
.B Miscellaneous
.PP
If your terminal correctly generates underlined characters (with no
special codes needed) even though the
it does not overstrike, then you should give the capability \fBul\fR;
If overstrikes are erasable with a blank, then this should be indicated
by giving \fBeo\fR.
.PP
If the terminal requires other than a null (zero) character as a pad,
then this can be given as \fBpc\fR.
.PP
If it has cursor motion keys
which generate single control characters, then the \fBma\fR option
can be set up to map these to the normal editor functions;
the map ``ma=^K^P'' maps a control-K, which moves the cursor up one line
on an \s-2ADM-3A\s0, to a control-P, which is the editor function to
move the cursor up one line.  Many pairs of characters may be given to
\fBma\fR.
.PP
If tabs on the terminal require padding, or if the terminal uses a
character other than \fB^I\fR to tab, then this can be given as \fBta\fR.
.PP
Hazeltine terminals, which don't allow `~' characters to be printed should
indicate \fBhz\fR.
Datamedia terminals, which echo carriage-return newline for carriage return
and then ignore a following newline should indicate \fBnc\fR.
Early Concept terminals, which ignore a newline immediately after an \fBam\fR
wrap, should indicate \fBxn\fR.
Other specific terminal problems may be corrected by adding more
capabilities of the form \fBx\fIx\fR.
.PP
Other capabilities utilized only by
.I tset (UCB)
include \fBis\fR, an initialization string for the terminal,
and \fBif\fR, the name of a file containing long initialization strings.
.SH FILES
.DT
/etc/termcap	file containing terminal descriptions
.SH SEE ALSO
ex (UCB), termlib (UCB), tset (UCB), vi (UCB)
.SH AUTHOR
William Joy
.SH BUGS
.I Ex
allows only 128 characters for string capabilities, and the routines
in 
.I termlib
do not check for overflow of this buffer.
.SH CAPABILITIES
.nf
(P) indicates padding may be specified
(P*) indicates that padding may be based on no. lines affected

.ta .7i 1.4i 2.1i
\fBName	Type	Pad?	Description\fR
al	str	(P*)	Add new blank line
am	bool		Terminal has automatic margins
bc	str		Back cursor if not \fB^H\fR
bs	bool		Terminal can backspace with \fB^H\fR
cd	str	(P*)	Clear to end of display
co	num		Number of columns in a line
ce	str	(P)	Clear to end of line
cl	str	(P*)	Clear screen
cm	str	(P)	Cursor motion
da	bool		Display may be retained above
db	bool		Display may be retained below
dc	str	(P*)	Delete character
dl	str	(P*)	Delete line
dm	str		Delete mode (enter)
ed	str		End delete mode
ei	str		End insert mode; give ``:ei=:'' if \fBic\fR
eo	str		Can erase overstrikes with a blank
ho	str		Home cursor (if no \fBcm\fR)
hz	str		Hazeltine; can't print ~'s
ic	str	(P)	Insert character
if	\-		Name of file containing \fBis\fR
im	bool		Insert mode (enter); give ``:im=:'' if \fBic\fR
in	bool		Insert mode distinguishes nulls on display
ip	str	(P*)	Insert pad after character inserted
is	str		Terminal initialization string
li	num		Number of lines on \s-2CRT\s0 screen
ll	str		Last line, first column (if no \fBcm\fR)
ma	str		Control character map for arrow keys
mi	bool		Safe to move while in insert mode
nc	bool		No correctly working carriage return (DM2500)
nd	str		Non-destructive space (cursor right)
os	bool		Terminal overstrikes
pc	str		Pad character (rather than null)
se	str		End stand out mode
sf	str	(P)	Scroll forwards
so	str		Begin stand out mode
sr	str	(P)	Scroll reverse (backwards)
ta	str	(P)	Tab (other than ^I or with padding)
ul	bool		Terminal underlines even though it doesn't overstrike
up	str		Upline (cursor up)
vb	str		Visible bell (may not move cursor)
ve	str		Sequence to end open/visual mode
vs	str		Sequence to start open/visual mode
xn	str		A newline is ignored after a wrap (Concept)