Name

termcap − terminal capability data base

Syntax

/etc/termcap

Description

The termcap file is a data base describing terminals used, for example, by vi() and curses(.). 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 fields separated by colons (:). The first entry for each terminal gives the names which are known for the terminal, separated by vertical bars (|). The first name is always two characters long and is used by older Version 6 systems, which store the terminal type in a 16-bit word in a system-wide 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 contain blanks for readability.

Capabilities

(P) indicates padding is commonly needed for these strings.
(P*) indicates that padding may be based on the number of lines affected.
 NameType Pad? Description
aestr(P)End alternate character set.
alstr(P*)Add new blank line.
amboolTerminal has automatic margins.
asstr(P)Start alternate character set.
bcstrBackspace, if not CTRL/H.
blstrAudible bell character.
bsboolTerminal can backspace with CTRL/H.
btstr(P)Back tab.
bwboolBackspace wraps from column 0 to last column.
CCstrCommand character in prototype, if terminal-settable.
caboolCursor addressable.
cdstr(P*)Clear to end of display.
cestr(P)Clear to end of line.
chstr(P)Like cm, but horizontal motion only; line stays the same.
clstr(P*)Clear screen.
cmstr(P)Cursor motion.
conumNumber of columns in a line.
crstr(P*)Carriage return (default CTRL/M).
csstr(P)Change scrolling region (VT100); like cm.
ct strClear all tab stops.
cvstr(P)Like ch, but vertical only.
daboolDisplay may be retained above.
dBnumNumber of millisec of bs delay needed.
dbboolDisplay may be retained below.
dCnumNumber of millisec of cr delay needed.
dcstr(P*)Delete character.
dFnumNumber of millisec of ff delay needed.
dlstr(P*)Delete line.
dmstrDelete mode (enter).
dNnumNumber of millisec of nl delay needed.
dostrMove down one line.
ds strClear host writable status line.
dTnumNumber of millisec of ta delay needed.
edstrEnd delete mode.
eistrEnd insert mode; give “:ei=:” if ic.
eostrCan erase overstrikes with a blank.
esboolStandout mode allowed on host writable status line.
ffstr(P*)Hard-copy terminal page eject (default CTRL/L).
fsstrClose host writable status line to writing.
gtboolGtty indicates tabs.
hcboolHard-copy terminal.
hdstrHalf-line down (forward 1/2 linefeed).
hostrHome cursor (if no cm).
hsboolHost writable status line capabilities.
hustrHalf-line up (reverse 1/2 linefeed).
hzstrHazeltine; cannot print tildes (~).
icstr(P)Insert character.
ifstrName of file containing is.
imboolInsert mode (enter); give “:im=:” if ic.
inboolInsert mode distinguishes nulls on display.
ipstr(P*)Insert pad after character inserted.
isstrTerminal initialization string.
k0-k9strSent by “other” function keys 0-9.
kbstrSent by backspace key.
kdstrSent by terminal down arrow key.
kestrOut of “keypad transmit” mode.
khstrSent by home key.
klstrSent by terminal left arrow key.
knnumNumber of “other” keys.
kostrTermcap entries for other nonfunction keys.
krstrSent by terminal right arrow key.
ksstrPut terminal in “keypad transmit” mode.
kustrSent by terminal up arrow key.
l0-l9strLabels on “other” function keys.
lestrMove cursor left one place.
linumNumber of lines on screen or page.
llstrLast line, first column (if no cm).
mastrArrow key map, used by vi Version 2 only.
mbstrTurn on blinking.
mdstrEnter bold (extra-bright) mode.
mestrTurn off all attributes, normal mode.
mhstrEnter dim (half-bright) mode.
miboolSafe to move while in insert mode.
mlstrMemory lock on above cursor.
mrstrEnter reverse mode.
msboolSafe to move while in standout and underline mode.
mustrMemory unlock (turn off memory lock).
ncboolNo correctly working carriage return (DM2500,H2000).
ndstrNondestructive space (cursor right).
nlstr(P*)Newline character (default \n).
nsboolTerminal is a CRT, but does not scroll.
osboolTerminal overstrikes.
pcstrPad character (rather than null).
ptboolHas hardware tabs (may need to be set with is).
rcstrRecover from last save cursor (sc).
rfstrReset file, like initialization file (if) but for reset.
rsstrReset string, like initialization string (is) but for reset.
sc strSave cursor.
sestrEnd stand out mode.
sfstr(P)Scroll forwards.
sgnumNumber of blank chars left by so or se.
sostrBegin stand out mode.
srstr(P)Scroll reverse (backwards).
ststrSave cursor.
tastr(P)Tab (other than CTRL/I or with padding).
tcstrEntry of similar terminal − must be last.
testrString to end programs that use cm.
tistrString to begin programs that use cm.
tsstrOpen host writable status line to writing.[jA.
ucstrUnderscore one char and move past it.
uestrEnd underscore mode.
ugnumNumber of blank chars left by us or ue.
ulboolTerminal underlines even though it does not overstrike.
upstrUpline (cursor up).
usstrStart underscore mode.
vbstrVisible bell (may not move cursor).
vestrSequence to end open/visual mode.
vsstrSequence to start open/visual mode.
vtnumVirtual terminal number.
xbboolBeehive (f1=escape, f2=CTRL/C).
xnboolA newline is ignored after a wrap (Concept).
xrboolReturn acts like ce \r \n (Delta Data).
xsboolStandout not erased by writing over it (HP 264?).
xtboolTabs are destructive, magic so char (Teleray 1061).

A Sample Entry

The following entry, which describes the Concept−100, is among the more complex entries in the termcap file as of this writing. 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:

Entries can continue onto multiple lines by giving a backslash (\) as the last character of a line. Empty fields can be included for readability (here between the last field on a line and the first field on the next). 

Types of Capabilities

Capabilities in termcap are of three types: Boolean capabilities that 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 that can be used to perform particular terminal operations.

All capabilities have two letter codes.  For instance, the fact that the Concept has “automatic margins” (that is, 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 number sign (#) 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 2-character code: an equal sign (=) and then a string ending at the next following colon (:).  A delay in milliseconds may appear after the equal sign (=) in such a capability. 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, for example, “20”, or an integer followed by 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 an asterisk (*) is specified, it is sometimes useful to give a delay of the form “3.5” to 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, O^x maps to a CTRL/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 backslash (\), and the characters circumflex (^) and backslash (\) may be given as \^ and \\.  If it is necessary to place a colon (:) 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 that 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. 

Preparing Descriptions

This section outlines 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, 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, it should have the am capability.  If the terminal can clear its screen, this is given by the cl string capability.  If the terminal can backspace, it should have the bs capability, unless a backspace is accomplished by a character other than ^H, 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, 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, that is, am. 

These capabilities suffice to describe hard-copy and “glass-tty” terminals.  Thus, the model 33 teletype is described as:

t3|33|tty33:co#72:os

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() types of escapes such as %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, its arguments are the line and then the column to which motion is desired, and the % encodings have the following meanings:

%dAs in printf, 0 origin
%2Like %2d
%3Like %3d
%.Like %c
%+xAdds x to value, then %.
%>xyIf value > x adds y, no output.
%rReverses order of line and column, no output
%iIncrements line/column (for 1 origin)
%%Gives a single %
%nExclusive or row and column with 0140 (DM2500)
%BBCD (16*(x/10)) + (x%10), no output.
%DReverse coding (x-2*(x%16)), no output. (Delta Data).

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 2ACT-IV needs the current row and column sent preceded by a ^T, with the row and column simply encoded in binary, “cm=^T%.%.”.  Terminals that 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 in the following section).  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, 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), 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, 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, 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, this can be given as sb, but just al suffices.  If the terminal can retain display memory above, the da capability should be given; if display memory can be retained below, db should be given.  These let the editor understand that deleting a line on the screen may bring nonblank lines up from below or that scrolling back with sb may bring down nonblank lines. 

Insert/Delete Character

There are two basic kinds of intelligent terminals with respect to insert/delete character that 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 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, your terminal does not distinguish between blanks and untyped positions.  If the “abc” shifts over to the “def” and then moves with it around the end of the current line and onto the next line 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, you may have to modify the editor to get it to use the insert mode your terminal defines.  Virtually all terminals that have an insert mode fallinto one of these two classes. 

The editor can handle both terminals that have an insert mode and terminals that 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).  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 that 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 that may need to be sent after an insert of a single character can also be given in ip. 

It is occasionally necessary to move around while in insert mode to delete characters on the same line (for example, 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 affects 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 kinds of standout mode, such as inverse video, blinking, or underlining.  Half-bright is not usually an acceptable “standout” mode, unless the terminal is in inverse video mode constantly.  The preferred mode is inverse video by itself.  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, ug should be given to tell how many spaces are left. 

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.) 

Many terminals, such as the HP 2621, automatically leave standout mode when they move to a new line or the cursor is addressed.  Programs using standout mode should exit standout mode before moving the cursor or sending a newline. 

If the terminal has a way of flashing the screen to indicate an error quietly (a bell replacement), 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, for example, from an 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 generates underlined characters, with no special codes needed, even though it does not overstrike, you should give the capability ul.  If overstrikes are erasable with a blank, 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 termcapP 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.

The ma entry is also used to indicate arrow keys on terminals that have single-character arrow keys.  It is obsolete, but still in use in Version 2 of vi, which must be run on some minicomputers due to memory limitations. This field is redundant with kl, kr, ku, kd, and kh.  It consists of groups of two characters.  In each group, the first character is what an arrow key sends, the second character is the corresponding vi command. These commands are h for kl, j for kd, k for ku, l for kr, and H for kh. For example, the Microterm Mime would be “ma=^Kj^Zk^Xl:” indicating arrow keys left (^H), down (^K), up (^Z), and right (^X). (There is no home key on the Mime.)

Miscellaneous

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

Hazeltine terminals, which do not allow tildes (~) to be printed, should indicate hz.  Datamedia terminals, which echo carriage-return linefeed for a 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.  If an erase-eol is required to get rid of standout (instead of merely writing on top of it), xs should be given.  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 is printed before if.  This is useful where if is /usr/lib/tabset/std but is clears the tabs first. 

Similar Terminals

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 canceled with xx@ where xx is the capability.  For example, the following entry 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:

hn|2621nl:ks@:ke@:tc=2621:

This is useful for different modes for a terminal or for different user preferences. 

Restrictions

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

The ma, vs, and ve entries are specific to the vi program.

Files

/etc/termcap File containing terminal descriptions

See Also

ex(1), more(1), tset(1), ul(1), vi(1), curses(3x), termcap(3x)