TERMCAP(5)

NAME
termcap - terminal capability data base

SYNOPSIS
/etc/termcap

DESCRIPTION
Termcap is a data base describing terminals. Terminals are described in 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 termcap.

Entries in 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.

CAPABILITIES
(P) indicates padding may be specified
(P*) indicates that padding may be based on no. lines affected
Name	Type	Pad?	Description
al	str	(P*)	Add new blank line
am	bool		Terminal has automatic margins
bc	str		Backspace if not ^H
bs	bool		Terminal can backspace with ^H
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
cr	str	(P*)	Carriage return, (default ^M)
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 ic
eo	str		Can erase overstrikes with a blank
ff	str	(P*)	Hardcopy terminal page eject (default ^L)
hc	bool		Hardcopy terminal
hd	str		Half-line down (forward 1/2 linefeed)
ho	str		Home cursor (if no cm)
hu	str		Half-line up (reverse 1/2 linefeed)
hz	str		Hazeltine; can't print ~'s
ic	str	(P)	Insert character
if	str		Name of file containing is
im	bool		Insert mode (enter); give ``:im=:'' if ic
in	bool		Insert mode distinguishes nulls on display
ip	str	(P*)	Insert pad after character inserted
is	str		Terminal initialization string
k0-k9	str		Sent by ``other'' function keys 0-9
kd	str		Sent by terminal down arrow key
ke	str		Out of ``keypad transmit'' mode
kl	str		Sent by terminal left arrow key
ko	str		Termcap entries for other non-function keys
kr	str		Sent by terminal right arrow key
ks	str		Put terminal in ``keypad transmit'' mode
ku	str		Sent by terminal up arrow key
l0-l9	str		Labels on ``other'' function keys
li	num		Number of lines on screen or page
ll	str		Last line, first column (if no cm)
mi	bool		Safe to move while in insert mode
nc	bool		No correctly working carriage return (DM2500,H2000)
nd	str		Non-destructive space (cursor right)
nl	str	(P*)	Newline character (default \n)
ns	bool		Terminal is a CRT but doesn't scroll.
os	bool		Terminal overstrikes
pc	str		Pad character (rather than null)
pt	bool		Has hardware tabs (may need to be set with is)
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)
tc	str		Entry of similar terminal - must be last
ti	str		String to begin programs that use cm
te	str		String to end programs that use cm
uc	str		Underscore one char and move past it
ue	str		End underscore mode
ul	bool		Terminal underlines even though it doesn't overstrike
up	str		Upline (cursor up)
us	str		Start underscore mode
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)
xt	bool		Tabs are destructive (Teleray 1061)

The following entry, which describes the Concept-100, is among the more complex entries in the termcap file as of this writing. (Note that this particular concept entry is outdated, and is used as an example only.)

c1|c100|concept100:is=\EU\Ef\E7\E5\E8\El\ENH\EK\E\200\Eo&\200:\
        :al=3*\E^R:am:bs:cd=16*\E^C:ce=16\E^S:cl=2*^L:cm=\Ea%+ %+ :co#80:\
        :dc=16\E^A:dl=3*\E^B:ei=\E\200:eo:im=\E^P:in:ip=16*:li#24:mi:nd=\E=:\
        :se=\Ed\Ee:so=\ED\EE:ta=8\t:ul:up=\E;:vb=\Ek\EK:xn:

Note that entries may continue onto multiple lines by giving a \ 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 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.

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 am. Hence the description of the Concept includes am. Numeric capabilities are followed by the character `#' and then the value. Thus co which indicates the number of columns the terminal has gives the value `80' for the Concept.

Finally, string valued capabilities, such as ce (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.

A number of escape sequences are provided in the string valued capabilities for easy encoding of characters there. A \E maps to an ESCAPE character, ^x maps to a control-x for any appropriate x, and the sequences \n \r \t \b \f give a newline, return, tab, backspace and formfeed. Finally, characters may be given as three octal digits after a \, and the characters ^ and \ may be given as \^ and \\. If it is necessary to place a : in a capability it must be escaped in octal as \072. If it is necessary to place a null character in a string capability it must be encoded as \200. The routines which deal with termcap use C strings, and strip the high bits of the output very late so that a \200 comes out as a \000 would.

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 termcap and to build up a description gradually, using partial descriptions with ex to check that they are correct. Be aware that a very unusual terminal may expose deficiencies in the ability of the termcap file to describe it or bugs in 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 /etc/termcap. TERMCAP can also be set to the termcap entry itself to avoid reading the file when starting up the editor. (This only works on version 7 systems.)

Basic capabilities

The number of columns on each line for the terminal is given by the co numeric capability. If the terminal is a CRT, then the number of lines on the screen is given by the li capability. If the terminal wraps around to the beginning of the next line when it reaches the right margin, then it should have the am capability. If the terminal can clear its screen, then this is given by the cl string capability. If the terminal can backspace, then it should have the bs capability, unless a backspace is accomplished by a character other than ^H (ugh) in which case you should give this character as the bc string capability. If it overstrikes (rather than clearing a position when a character is struck over) then it should have the os capability.

A very important point here is that the local cursor motions encoded in termcap are undefined at the left and top edges of a CRT 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 am capability tells whether the cursor sticks at the right edge of the screen. If the terminal has switch selectable automatic margins, the termcap file usually assumes that this is on, i.e. am.

These capabilities suffice to describe hardcopy and ``glass-tty'' terminals. Thus the model 33 teletype is described as

    t3|33|tty33:co#72:os

while the Lear Siegler ADM-3 is described as

    cl|adm3|3|lsi adm3:am:bs:cl=^Z:li#24:co#80

Cursor addressing

Cursor addressing in the terminal is described by a cm string capability, with printf(3s) like escapes %x in it. These substitute to encodings of the current line or column position, while other characters are passed through unchanged. If the cm 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 % encodings have the following meanings:

	%d	as in printf, 0 origin
	%2	like %2d
	%3	like %3d
	%.	like %c
	%+x	adds x 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)

Consider the HP2645, which, to get to row 3 and column 12, needs to be sent \E&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 cm capability is ``cm=6\E&%r%2c%2Y''. The Microterm ACT-IV needs the current row and column sent preceded by a ^T, with the row and column simply encoded in binary, ``cm=^T%.%.''. Terminals which use ``%.'' need to be able to backspace the cursor (bs or bc), and to move the cursor up one line on the screen (up introduced below). This is necessary because it is not always safe to transmit \t, \n ^D and \r, as the system may change or discard them.

A final example is the LSI ADM-3a, which uses row and column offset by a blank character, thus ``cm=\E=%+ %+ ''.

Cursor motions

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 nd (non-destructive space). If it can move the cursor up a line on the screen in the same column, this should be given as up. If the terminal has no cursor addressing capability, but can home the cursor (to very upper left corner of screen) then this can be given as ho; similarly a fast way of getting to the lower left hand corner can be given as ll; this may involve going up with up from the home position, but the editor will never do this itself (unless ll does) because it makes no assumption about the effect of moving up from the home position.

Area clears

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 ce. If the terminal can clear from the current position to the end of the display, then this should be given as cd. The editor only uses cd from the first column of a line.

Insert/delete line

If the terminal can open a new blank line before the line where the cursor is, this should be given as al; 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 dl; 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 sb, but just al suffices. If the terminal can retain display memory above then the da capability should be given; if display memory can be retained below then db 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 sb may bring down non-blank lines.

Insert/delete character

There are two basic kinds of intelligent terminals with respect to insert/delete character which can be described using 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 in, 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.

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 im 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 ei the sequence to leave insert mode (give this, with an empty value also if you gave im so). Now give as ic any sequence needed to be sent just before sending the character to be inserted. Most terminals with a true insert mode will not give ic, 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 ip (a string option). Any other sequence which may need to be sent after an insert of a single character may also be given in ip.

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 mi to speed up inserting in this case. Omitting mi will affect only speed. Some terminals (notably Datamedia's) must not have mi because of the way their insert mode works.

Finally, you can specify delete mode by giving dm and ed to enter and exit delete mode, and dc to delete a single character while in delete mode.

Highlighting, underlining, and visible bells

If your terminal has sequences to enter and exit standout mode these can be given as so and se respectively. If there are several flavors of standout mode (such as inverse video, blinking, or underlining - half bright is not considered ``standout'') the prefered mode is inverse video by itself. It doesn't matter if the code to change into or out of standout mode leaves one or even two blank spaces on the screen, as the TVI 912 and Teleray 1061 do.

Codes to begin underlining and end underlining can be given as us and ue respectively. If the terminal has a code to underline the current character and move the cursor one space to the right, such as the Microterm Mime, this can be given as uc. (If the underline code does not move the cursor to the right, give the code followed by a nondestructive space.)

If the terminal has a way of flashing the screen to indicate an error quietly (a bell replacement) then this can be given as vb; it must not move the cursor. If the terminal should be placed in a different mode during open and visual modes of ex, this can be given as vs and ve, 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.

If the terminal needs to be in a special mode when running a program that addresses the cursor, the codes to enter and exit this mode can be given as ti and te. This arises, for example, from terminals like the Concept with more than one page of memory. If the terminal has only memory relative cursor addressing and not screen relative cursor addressing, a one screen-sized window must be fixed into the terminal for cursor addressing to work properly.

If your terminal correctly generated underlined characters (with no special codes needed) enen though it does not overstrike, then you should give the capability ul. If overstrikes are erasable with a blank, then this should be indicated by giving eo.

Keypad

If the terminal has a keypad that transmits codes when the keys are pressed, this information can be given. Note that it is not possible to handle terminals where the keypad only works in local (this applies, for example, to the unshifted HP 2621 keys). If the keypad can be set to transmit or not transmit, give these codes as ks and ke. Otherwise the keypad is assumed to always transmit. The codes sent by the left arrow, right arrow, up arrow, down arrow, and home keys can be given as kl, kr, ku, kd, and kh respectively. If there are function keys such as f0, f1, ..., f9, the codes they send can be given as k0, k1, ..., k9. If these keys have labels other than the default f0 through f9, the labels can be given as l0, l1, ..., l9. If there are other keys that transmit the same code as the terminal expects for the corresponding function, such as clear screen, the termcap 2 letter codes can be given in the ko capability, for example, ``:ko=cl,ll,sf,sb:'', which says that the terminal has clear, home down, scroll down, and scroll up keys that transmit the same thing as the cl, ll, sf, and sb entries.

Miscellaneous

If the terminal requires other than a null (zero) character as a pad, then this can be given as pc.

If tabs on the terminal require padding, or if the terminal uses a character other than ^I to tab, then this can be given as ta.

Hazeltine terminals, which don't allow `~' characters to be printed should indicate hz. Datamedia terminals, which echo carriage-return linefeed for carriage return and then ignore a following linefeed should indicate nc. Early Concept terminals, which ignore a linefeed immediately after an am wrap, should indicate xn. Teleray terminals, where tabs turn all characters moved over to blanks, should indicate xt. Other specific terminal problems may be corrected by adding more capabilities of the form xx.

Other capabilities include is, an initialization string for the terminal, and if, the name of a file containing long initialization strings. These strings are expected to properly clear and then set the tabs on the terminal, if the terminal has settable tabs. If both are given, is will be printed before if. This is useful where if is /usr/lib/tabset/std but is clears the tabs first.

If there are two very similar terminals, one can be defined as being just like the other with certain exceptions. The string capability tc can be given with the name of the similar terminal. This capability must be last and the combined length of the two entries must not exceed 1024. Since termlib routines search the entry from left to right, and since the tc capability is replaced by the corresponding entry, the capabilities given at the left override the ones in the similar terminal. A capability can be cancelled with xx@ where xx is the capibility. For example, the entry
    hn|2621nl:ks@:ke@:tc=2621:
defines a 2621nl that does not have the ks or ke capabilities, and hence does not turn on the function key labels when in visual mode. This is useful for different modes for a terminal, or for different user preferences.

FILES
/etc/termcap    file containing terminal descriptions

SEE ALSO
ex(1), termlib(3), tset(1), vi(1), ul(1), more(1)

AUTHOR
William Joy
Mark Horton added underlining and keypad support

BUGS
Ex allows only 256 characters for string capabilities, and the routines in termlib do not check for overflow of this buffer. The total length of a single entry (excluding only escaped newlines) may not exceed 1024.