Info file ../info/termcap, produced by Makeinfo, -*- Text -*- from
input file termcap.texinfo.

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,  Node: Top,  Next: Introduction,  Prev: (DIR),  Up: (DIR)

* Menu:

* Introduction::What is termcap?  Why this manual?
* Library::     The termcap library functions.
* Data Base::   What terminal descriptions in `/etc/termcap' look like.
* Capabilities::Definitions of the individual terminal capabilities:
                 how to write them in descriptions, and how to use
                 their values to do display updating.
* Summary::	Brief table of capability names and their meanings.
* Var Index::   Index of C functions and variables.
* Cap Index::   Index of termcap capabilities.
* Index::       Concept index.


File: termcap,  Node: Introduction,  Next: Library,  Prev: Top,  Up: Top


"Termcap" is a library and data base that enables programs to use
display terminals in a terminal-independent manner.  It originated in
Berkeley Unix.

The termcap data base describes the capabilities of hundreds of
different display terminals in great detail.  Some examples of the
information recorded for a terminal could include how many columns
wide it is, what string to send to move the cursor to an arbitrary
position (including how to encode the row and column numbers), how to
scroll the screen up one or several lines, and how much padding is
needed for such a scrolling operation.

The termcap library is provided for easy access this data base in
programs that want to do terminal-independent character-based display

This manual describes the GNU version of the termcap library, which
has some extensions over the Unix version.  All the extensions are
identified as such, so this manual also tells you how to use the Unix

The GNU version of the termcap library is available free as source
code, for use in free programs, and runs on Unix and VMS systems (at
least).  You can find it in the GNU Emacs distribution in the files
`termcap.c' and `tparam.c'.

This manual was written for the GNU project, whose goal is to develop
a complete free operating system upward-compatible with Unix for user
programs.  The project is approximately two thirds complete.  For
more information on the GNU project, including the GNU Emacs editor
and the mostly-portable optimizing C compiler, send one dollar to

     Free Software Foundation
     675 Mass Ave
     Cambridge, MA 02139

File: termcap,  Node: Library,  Next: Data Base,  Prev: Introduction,  Up: Top

The Termcap Library

The termcap library is the application programmer's interface to the
termcap data base.  It contains functions for the following purposes:

   * Finding the description of the user's terminal type (`tgetent').

   * Interrogating the description for information on various topics
     (`tgetnum', `tgetflag', `tgetstr').

   * Computing and performing padding (`tputs').

   * Encoding numeric parameters such as cursor positions into the
     terminal-specific form required for display commands (`tparam',

* Menu:

* Preparation:: Preparing to use the termcap library.
* Find::        Finding the description of the terminal being used.
* Interrogate:: Interrogating the description for particular capabilities.
* Initialize::  Initialization for output using termcap.
* Padding::     Outputting padding.
* Parameters::  Encoding parameters such as cursor positions.


File: termcap,  Node: Preparation,  Next: Find,  Prev: Library,  Up: Library

Preparing to Use the Termcap Library

To use the termcap library in a program, you need two kinds of

   * The compiler needs declarations of the functions and variables
     in the library.

     On GNU systems, it suffices to include the header file
     `termcap.h' in each source file that uses these functions and

     On Unix systems, there is often no such header file.  Then you
     must explictly declare the variables as external.  You can do
     likewise for the functions, or let them be implicitly declared
     and cast their values from type `int' to the appropriate type.

     We illustrate the declarations of the individual termcap library
     functions with ANSI C prototypes because they show how to pass
     the arguments.  If you are not using the GNU C compiler, you
     probably cannot use function prototypes, so omit the argument
     types and names from your declarations.

   * The linker needs to search the library.  Usually either
     `-ltermcap' or `-ltermlib' as an argument when linking will do

File: termcap,  Node: Find,  Next: Interrogate,  Prev: Preparation,  Up: Library

Finding a Terminal Description: `tgetent'

An application program that is going to use termcap must first look
up the description of the terminal type in use.  This is done by
calling `tgetent', whose declaration in ANSI Standard C looks like:

     int tgetent (char *BUFFER, char *TERMTYPE);

This function finds the description and remembers it internally so
that you can interrogate it about specific terminal capabilities
(*note Interrogate::.).

The argument TERMTYPE is a string which is the name for the type of
terminal to look up.  Usually you would obtain this from the
environment variable `TERM' using `getenv ("TERM")'.

If you are using the GNU version of termcap, you can alternatively
ask `tgetent' to allocate enough space.  Pass a null pointer for
BUFFER, and `tgetent' itself allocates the storage using `malloc'. 
In this case the returned value on success is the address of the
storage, cast to `int'.  But normally there is no need for you to
look at the address.  Do not free the storage yourself.

With the Unix version of termcap, you must allocate space for the
description yourself and pass the address of the space as the
argument BUFFER.  There is no way you can tell how much space is
needed, so the convention is to allocate a buffer 2048 characters
long and assume that is enough.  (Formerly the convention was to
allocate 1024 characters and assume that was enough.  But one day,
for one kind of terminal, that was not enough.)

No matter how the space to store the description has been obtained,
termcap records its address internally for use when you later
interrogate the description with `tgetnum', `tgetstr' or `tgetflag'. 
If the buffer was allocated by termcap, it will be freed by termcap
too if you call `tgetent' again.  If the buffer was provided by you,
you must make sure that its contents remain unchanged for as long as
you still plan to interrogate the description.

The return value of `tgetent' is -1 if there is some difficulty
accessing the data base of terminal types, 0 if the data base is
accessible but the specified type is not defined in it, and some
other value otherwise.

Here is how you might use the function `tgetent':

     #ifdef unix
     static char term_buffer[2048];
     #define term_buffer 0
     init_terminal_data ()
       char *termtype = getenv ("TERM");
       int success;
       if (termtype == 0)
         fatal ("Specify a terminal type with `setenv TERM <yourtype>'.\n");
       success = tgetent (term_buffer, termtype);
       if (success < 0)
         fatal ("Could not access the termcap data base.\n");
       if (success == 0)
         fatal ("Terminal type `%s' is not defined.\n", termtype);

Here we assume the function `fatal' prints an error message and exits.

If the environment variable `TERMCAP' is defined, its value is used
to override the terminal type data base.  The function `tgetent'
checks the value of `TERMCAP' automatically.  If the value starts
with `/' then it is taken as a file name to use as the data base
file, instead of `/etc/termcap' which is the standard data base.  If
the value does not start with `/' then it is itself used as the
terminal description, provided that the terminal type TERMTYPE is
among the types it claims to apply to.  *Note Data Base::, for
information on the format of a terminal description.

File: termcap,  Node: Interrogate,  Next: Initialize,  Prev: Find,  Up: Library

Interrogating the Terminal Description

Each piece of information recorded in a terminal description is
called a "capability".  Each defined terminal capability has a
two-letter code name and a specific meaning.  For example, the number
of columns is named `co'.  *Note Capabilities::, for definitions of
all the standard capability names.

Once you have found the proper terminal description with `tgetent'
(*note Find::.), your application program must "interrogate" it for
various terminal capabilities.  You must specify the two-letter code
of the capability whose value you seek.

Capability values can be numeric, boolean (capability is either
present or absent) or strings.  Any particular capability always has
the same value type; for example, `co' always has a numeric value,
while `am' (automatic wrap at margin) is always a flag, and `cm'
(cursor motion command) always has a string value.  The documentation
of each capability says which type of value it has.

There are three functions to use to get the value of a capability,
depending on the type of value the capability has.  Here are their
declarations in ANSI C:

     int tgetnum (char *NAME);
     int tgetflag (char *NAME);
     char *tgetstr (char *NAME, char **AREA);

     Use `tgetnum' to get a capability value that is numeric.  The
     argument NAME is the two-letter code name of the capability.  If
     the capability is present, `tgetnum' returns the numeric value
     (which is nonnegative).  If the capability is not mentioned in
     the terminal description, `tgetnum' returns -1.

     Use `tgetflag' to get a boolean value.  If the capability NAME
     is present in the terminal description, `tgetflag' returns 1;
     otherwise, it returns 0.

     Use `tgetstr' to get a string value.  It returns a pointer to a
     string which is the capability value, or a null pointer if the
     capability is not present in the terminal description.

     There are two ways `tgetstr' can find space to store the string

        * You can ask `tgetstr' to allocate the space.  Pass a null
          pointer for the argument AREA, and `tgetstr' will use
          `malloc' to allocate storage big enough for the value. 
          Termcap will never free this storage or refer to it again;
          you should free it when you are finished with it.

          This method is more robust, since there is no need to guess
          how much space is needed.  But it is supported only by the
          GNU termcap library.

        * You can provide the space.  Provide for the argument AREA
          the address of a pointer variable of type `char *'.  Before
          calling `tgetstr', initialize the variable to point at
          available space.  Then `tgetstr' will store the string
          value in that space and will increment the pointer variable
          to point after the space that has been used.  You can use
          the same pointer variable for many calls to `tgetstr'.

          There is no way to determine how much space is needed for a
          single string, and no way for you to prevent or handle
          overflow of the area you have provided.  However, you can
          be sure that the total size of all the string values you
          will obtain from the terminal description is no greater
          than the size of the description (unless you get the same
          capability twice).  You can determine that size with
          `strlen' on the buffer you provided to `tgetent'.  See
          below for an example.

          Providing the space yourself is the only method supported
          by the Unix version of termcap.

Note that you do not have to specify a terminal type or terminal
description for the interrogation functions.  They automatically use
the description found by the most recent call to `tgetent'.

Here is an example of interrogating a terminal description for
various capabilities, with conditionals to select between the Unix
and GNU methods of providing buffer space.

     char *tgetstr ();
     char *cl_string, *cm_string;
     int height;
     int width;
     int auto_wrap;
     char PC;   /* For tputs.  */
     char *BC;  /* For tgoto.  */
     char *UP;
     interrogate_terminal ()
     #ifdef UNIX
       /* Here we assume that an explicit term_buffer
          was provided to tgetent.  */
       char *buffer
         = (char *) malloc (strlen (term_buffer));
     #define BUFFADDR &buffer
     #define BUFFADDR 0
       char *temp;
       /* Extract information we will use.  */
       cl_string = tgetstr ("cl", BUFFADDR);
       cm_string = tgetstr ("cm", BUFFADDR);
       auto_wrap = tgetflag ("am");
       height = tgetnum ("li");
       width = tgetnum ("co");
       /* Extract information that termcap functions use.  */
       temp = tgetstr ("pc", BUFFADDR);
       PC = temp ? *temp : 0;
       BC = tgetstr ("le", BUFFADDR);
       UP = tgetstr ("up", BUFFADDR);

*Note Padding::, for information on the variable `PC'.  *Note Using
Parameters::, for information on `UP' and `BC'.

File: termcap,  Node: Initialize,  Next: Padding,  Prev: Interrogate,  Up: Library

Initialization for Use of Termcap

Before starting to output commands to a terminal using termcap, an
application program should do two things:

   * Initialize various global variables which termcap library output
     functions refer to.  These include `PC' and `ospeed' for padding
     (*note Output Padding::.) and `UP' and `BC' for cursor motion
     (*note tgoto::.).

   * Tell the kernel to turn off alteration and padding of
     horizontal-tab characters sent to the terminal.

To turn off output processing in Berkeley Unix you would use `ioctl'
with code `TIOCLSET' to set the bit named `LLITOUT', and clear the
bits `ANYDELAY' using `TIOCSETN'.  In POSIX or System V, you must
clear the bit named `OPOST'.  Refer to the system documentation for

If you do not set the terminal flags properly, some older terminals
will not work.  This is because their commands may contain the
characters that normally signify newline, carriage return and
horizontal tab--characters which the kernel thinks it ought to modify
before output.

When you change the kernel's terminal flags, you must arrange to
restore them to their normal state when your program exits.  This
implies that the program must catch fatal signals such as `SIGQUIT'
and `SIGINT' and restore the old terminal flags before actually

Modern terminals' commands do not use these special characters, so if
you do not care about problems with old terminals, you can leave the
kernel's terminal flags unaltered.

File: termcap,  Node: Padding,  Next: Parameters,  Prev: Initialize,  Up: Library


"Padding" means outputting null characters following a terminal
display command that takes a long time to execute.  The terminal
description says which commands require padding and how much; the
function `tputs', described below, outputs a terminal command while
extracting from it the padding information, and then outputs the
padding that is necessary.

* Menu:

* Why Pad::          Explanation of padding.
* Describe Padding:: The data base says how much padding a terminal needs.
* Output Padding::   Using `tputs' to output the needed padding.


File: termcap,  Node: Why Pad,  Next: Describe Padding,  Prev: Padding,  Up: Padding

Why Pad, and How

Most types of terminal have commands that take longer to execute than
they do to send over a high-speed line.  For example, clearing the
screen may take 20msec once the entire command is received.  During
that time, on a 9600 bps line, the terminal could receive about 20
additional output characters while still busy clearing the screen. 
Every terminal has a certain amount of buffering capacity to remember
output characters that cannot be processed yet, but too many slow
commands in a row can cause the buffer to fill up.  Then any
additional output that cannot be processed immediately will be lost.

To avoid this problem, we normally follow each display command with
enough useless charaters (usually null characters) to fill up the
time that the display command needs to execute.  This does the job if
the terminal throws away null characters without using up space in
the buffer (which most terminals do).  If enough padding is used, no
output can ever be lost.  The right amount of padding avoids loss of
output without slowing down operation, since the time used to
transmit padding is time that nothing else could be done.

The number of padding characters needed for an operation depends on
the line speed.  In fact, it is proportional to the line speed.  A
9600 baud line transmits about one character per msec, so the clear
screen command in the example above would need about 20 characters of
padding.  At 1200 baud, however, only about 3 characters of padding
are needed to fill up 20msec.

File: termcap,  Node: Describe Padding,  Next: Output Padding,  Prev: Why Pad,  Up: Padding

Specifying Padding in a Terminal Description

In the terminal description, the amount of padding required by each
display command is recorded as a sequence of digits at the front of
the command.  These digits specify the padding time in msec.  They
can be followed optionally by a decimal point and one more digit,
which is a number of tenths of msec.

Sometimes the padding needed by a command depends on the cursor
position.  For example, the time taken by an "insert line" command is
usually proportional to the number of lines that need to be moved
down or cleared.  An asterisk (`*') following the padding time says
that the time should be multiplied by the number of screen lines
affected by the command.


is used to describe the "insert line" command for a certain terminal.
The padding required is 1.3 msec per line affected.  The command
itself is `ESC [ L'.

The padding time specified in this way tells `tputs' how many pad
characters to output.  *Note Output Padding::.

Two special capability values affect padding for all commands.  These
are the `pc' and `pb'.  The variable `pc' specifies the character to
pad with, and `pb' the speed below which no padding is needed.  The
defaults for these variables, a null character and 0, are correct for
most terminals.  *Note Pad Specs::.

File: termcap,  Node: Output Padding,  Prev: Describe Padding,  Up: Padding

Performing Padding with `tputs'

Use the termcap function `tputs' to output a string containing an
optional padding spec of the form described above (*note Describe
Padding::.).  The function `tputs' strips off and decodes the padding
spec, outputs the rest of the string, and then outputs the
appropriate padding.  Here is its declaration in ANSI C:

     char PC;
     short ospeed;
     int tputs (char *STRING, int NLINES, int (*OUTFUN) ());

Here STRING is the string (including padding spec) to be output;
NLINES is the number of lines affected by the operation, which is
used to multiply the amount of padding if the padding spec ends with
a `*'.  Finally, OUTFUN is a function (such as `fputchar') that is
called to output each character.  When actually called, OUTFUN should
expect one argument, a character.

The operation of `tputs' is controlled by two global variables,
`ospeed' and `PC'.  The value of `ospeed' is supposed to be the
terminal output speed, encoded as in the `ioctl' system call which
gets the speed information.  This is needed to compute the number of
padding characters.  The value of `PC' is the character used for

You are responsible for storing suitable values into these variables
before using `tputs'.  The value stored into the `PC' variable should
be taken from the `pc' capability in the terminal description (*note
Pad Specs::.).  Store zero in `PC' if there is no `pc' capability.

The argument NLINES requires some thought.  Normally, it should be
the number of lines whose contents will be cleared or moved by the
command.  For cursor motion commands, or commands that do editing
within one line, use the value 1.  For most commands that affect
multiple lines, such as `al' (insert a line) and `cd' (clear from the
cursor to the end of the screen), NLINES should be the screen height
minus the current vertical position (origin 0).  For multiple insert
and scroll commands such as `AL' (insert multiple lines), that same
value for NLINES is correct; the number of lines being inserted is
not correct.

If a "scroll window" feature is used to reduce the number of lines
affected by a command, the value of NLINES should take this into
account.  This is because the delay time required depends on how much
work the terminal has to do, and the scroll window feature reduces
the work.  *Note Scrolling::.

Commands such as `ic' and `dc' (insert or delete characters) are
problematical because the padding needed by these commands is
proportional to the number of characters affected, which is the
number of columns from the cursor to the end of the line.  It would
be nice to have a way to specify such a dependence, and there is no
need for dependence on vertical position in these commands, so it is
an obvious idea to say that for these commands NLINES should really
be the number of columns affected.  However, the definition of
termcap clearly says that NLINES is always the number of lines
affected, even in this case, where it is always 1.  It is not easy to
change this rule now, because too many programs and terminal
descriptions have been written to follow it.

Because NLINES is always 1 for the `ic' and `dc' strings, there is no
reason for them to use `*', but some of them do.  These should be
corrected by deleting the `*'.  If, some day, such entries have
disappeared, it may be possible to change to a more useful convention
for the NLINES argument for these operations without breaking any

File: termcap,  Node: Parameters,  Prev: Padding,  Up: Library

Filling In Parameters

Some terminal control strings require numeric "parameters".  For
example, when you move the cursor, you need to say what horizontal
and vertical positions to move it to.  The value of the terminal's
`cm' capability, which says how to move the cursor, cannot simply be
a string of characters; it must say how to express the cursor
position numbers and where to put them within the command.

The specifications of termcap include conventions as to which
string-valued capabilities require parameters, how many parameters,
and what the parameters mean; for example, it defines the `cm' string
to take two parameters, the vertical and horizontal positions, with
0,0 being the upper left corner.  These conventions are described
where the individual commands are documented.

Termcap also defines a language used within the capability definition
for specifying how and where to encode the parameters for output. 
This language uses character sequences starting with `%'.  (This is
the same idea as `printf', but the details are different.)  The
language for parameter encoding is described in this section.

A program that is doing display output calls the functions `tparam'
or `tgoto' to encode parameters according to the specifications. 
These functions produce a string containing the actual commands to be
output (as well a padding spec which must be processed with `tputs';
*note Padding::.).

* Menu:

* Encode Parameters:: The language for encoding parameters.
* Using Parameters::  Outputting a string command with parameters.


File: termcap,  Node: Encode Parameters,  Next: Using Parameters,  Prev: Parameters,  Up: Parameters

Describing the Encoding

A terminal command string that requires parameters contains special
character sequences starting with `%' to say how to encode the
parameters.  These sequences control the actions of `tparam' and

The parameters values passed to `tparam' or `tgoto' are considered to
form a vector.  A pointer into this vector determines the next
parameter to be processed.  Some of the `%'-sequences encode one
parameter and advance the pointer to the next parameter.  Other
`%'-sequences alter the pointer or alter the parameter values without
generating output.

For example, the `cm' string for a standard ANSI terminal is written
as `\E[%i%d;%dH'.  (`\E' stands for ESC.)  `cm' by convention always
requires two parameters, the vertical and horizontal goal positions,
so this string specifies the encoding of two parameters.  Here `%i'
increments the two values supplied, and each `%d' encodes one of the
values in decimal.  If the cursor position values 20,58 are encoded
with this string, the result is `\E[21;59H'.

First, here are the `%'-sequences that generate output.  Except for
`%%', each of them encodes one parameter and advances the pointer to
the following parameter.

     Output a single `%'.  This is the only way to represent a
     literal `%' in a terminal command with parameters.  `%%' does
     not use up a parameter.

     As in `printf', output the next parameter in decimal.

     Like `%02d' in `printf': output the next parameter in decimal,
     and always use at least two digits.

     Like `%03d' in `printf': output the next parameter in decimal,
     and always use at least three digits.  Note that `%4' and so on
     are *not* defined.

     Output the next parameter as a single character whose ASCII code
     is the parameter value.  Like `%c' in `printf'.

     Add the next parameter to the character CHAR, and output the
     resulting character.  For example, `%+ ' represents 0 as a
     space, 1 as `!', etc.

The following `%'-sequences specify alteration of the parameters
(their values, or their order) rather than encoding a parameter for
output.  They generate no output; they are used only for their side
effects on the parameters.  Also, they do not advance the "next
parameter" pointer except as explicitly stated.  Only `%i', `%r' and
`%>' are defined in standard Unix termcap.  The others are GNU

     Increment the next two parameters.  This is used for terminals
     that expect cursor positions in origin 1.  For example,
     `%i%d,%d' would output two parameters with `1' for 0, `2' for 1,

     Interchange the next two parameters.  This is used for terminals
     whose cursor positioning command expects the horizontal position

     Skip the next parameter.  Do not output anything.

     Back up one parameter.  The last parameter used will become once
     again the next parameter to be output, and the next output
     command will use it.  Using `%b' more than once, you can back up
     any number of parameters, and you can refer to each parameter
     any number of times.

     Conditionally increment the next parameter.  Here C1 and C2 are
     characters which stand for their ASCII codes as numbers.  If the
     next parameter is greater than the ASCII code of C1, the ASCII
     code of C2 is added to it.

     Perform arithmetic on the next parameter, do not use it up, and
     do not output anything.  Here OP specifies the arithmetic
     operation, while TYPE and POS together specify the other operand.

     Spaces are used above to separate the operands for clarity; the
     spaces don't appear in the data base, where this sequence is
     exactly five characters long.

     The character OP says what kind of arithmetic operation to
     perform.  It can be any of these characters:

          assign a value to the next parameter, ignoring its old value.
          The new value comes from the other operand.

          add the other operand to the next parameter.

          subtract the other operand from the next parameter.

          multiply the next parameter by the other operand.

          divide the next parameter by the other operand.

     The "other operand" may be another parameter's value or a
     constant; the character TYPE says which.  It can be:

          Use another parameter.  The character POS says which
          parameter to use.  Subtract 64 from its ASCII code to get
          the position of the desired parameter relative to this one.
          Thus, the character `A' as POS means the parameter after
          the next one; the character `?' means the parameter before
          the next one.

          Use a constant value.  The character POS specifies the
          value of the constant.  The 0200 bit is cleared out, so
          that 0200 can be used to represent zero.

The following `%'-sequences are special purpose hacks to compensate
for the weird designs of obscure terminals.  They modify the next
parameter or the next two parameters but do not generate output and
do not use up any parameters.  `%m' is a GNU extension; the others
are defined in standard Unix termcap.

     Exclusive-or the next parameter with 0140, and likewise the
     parameter after next.

     Complement all the bits of the next parameter and the parameter
     after next.

     Encode the next parameter in BCD.  It alters the value of the
     parameter by adding six times the quotient of the parameter by
     ten.  Here is a C statement that shows how the new value is

          PARM = (PARM / 10) * 16 + PARM % 10;

     Transform the next parameter as needed by Delta Data terminals. 
     This involves subtracting twice the remainder of the parameter
     by 16.

          PARM -= 2 * (PARM % 16);

File: termcap,  Node: Using Parameters,  Prev: Encode Parameters,  Up: Parameters

Sending Display Commands with Parameters

The termcap library functions `tparam' and `tgoto' serve as the
analog of `printf' for terminal string parameters.  The newer
function `tparam' is a GNU extension, more general but missing from
Unix termcap.  The original parameter-encoding function is `tgoto',
which is preferable for cursor motion.

* Menu:

* tparam::   The general case, for GNU termcap only.
* tgoto::    The special case of cursor motion.


File: termcap,  Node: tparam,  Next: tgoto,  Prev: Using Parameters,  Up: Using Parameters


 The function `tparam' can encode display commands with any number of
parameters and allows you to specify the buffer space.  It is the
preferred function for encoding parameters for all but the `cm'
capability.  Its ANSI C declaration is as follows:

     char *tparam (char *CTLSTRING, char *BUFFER, int SIZE, int PARM1,...)

The arguments are a control string CTLSTRING (the value of a terminal
capability, presumably), an output buffer BUFFER and SIZE, and any
number of integer parameters to be encoded.  The effect of `tparam'
is to copy the control string into the buffer, encoding parameters
according to the `%' sequences in the control string.

You describe the output buffer by its address, BUFFER, and its size
in bytes, SIZE.  If the buffer is not big enough for the data to be
stored in it, `tparam' calls `malloc' to get a larger buffer.  In
either case, `tparam' returns the address of the buffer it ultimately
uses.  If the value equals BUFFER, your original buffer was used. 
Otherwise, a new buffer was allocated, and you must free it after you
are done with printing the results.  If you pass zero for SIZE and
BUFFER, `tparam' always allocates the space with `malloc'.

All capabilities that require parameters also have the ability to
specify padding, so you should use `tputs' to output the string
produced by `tparam'.  *Note Padding::.  Here is an example.

       char *buf;
       char buffer[40];
       buf = tparam (command, buffer, 40, parm);
       tputs (buf, 1, fputchar);
       if (buf != buffer)
         free (buf);

If a parameter whose value is zero is encoded with `%.'-style
encoding, the result is a null character, which will confuse `tputs'.
This would be a serious problem, but luckily `%.' encoding is used
only by a few old models of terminal, and only for the `cm'
capability.  To solve the problem, use `tgoto' rather than `tparam'
to encode the `cm' capability.

File: termcap,  Node: tgoto,  Prev: tparam,  Up: Using Parameters


 The special case of cursor motion is handled by `tgoto'.  There are
two reasons why you might choose to use `tgoto':

   * For Unix compatibility, because Unix termcap does not have

   * For the `cm' capability, since `tgoto' has a special feature to
     avoid problems with null characters, tabs and newlines on
     certain old terminal types that use `%.' encoding for that

Here is how `tgoto' might be declared in ANSI C:

     char *tgoto (char *CSTRING, int HPOS, int VPOS)

There are three arguments, the terminal description's `cm' string and
the two cursor position numbers; `tgoto' computes the parametrized
string in an internal static buffer and returns the address of that
buffer.  The next time you use `tgoto' the same buffer will be reused.

Parameters encoded with `%.' encoding can generate null characters,
tabs or newlines.  These might cause trouble: the null character
because `tputs' would think that was the end of the string, the tab
because the kernel or other software might expand it into spaces, and
the newline becaue the kernel might add a carriage-return, or padding
characters normally used for a newline.  To prevent such problems,
`tgoto' is careful to avoid these characters.  Here is how this
works: if the target cursor position value is such as to cause a
problem (that is to say, zero, nine or ten), `tgoto' increments it by
one, then compensates by appending a string to move the cursor back
or up one position.

The compensation strings to use for moving back or up are found in
global variables named `BC' and `UP'.  These are actual external C
variables with upper case names; they are declared `char *'.  It is
up to you to store suitable values in them, normally obtained from
the `le' and `up' terminal capabilities in the terminal description
with `tgetstr'.  Alternatively, if these two variables are both zero,
the feature of avoiding nulls, tabs and newlines is turned off.

It is safe to use `tgoto' for commands other than `cm' only if you
have stored zero in `BC' and `UP'.

Note that `tgoto' reverses the order of its operands: the horizontal
position comes before the vertical position in the arguments to
`tgoto', even though the vertical position comes before the
horizontal in the parameters of the `cm' string.  If you use `tgoto'
with a command such as `AL' that takes one parameter, you must pass
the parameter to `tgoto' as the "vertical position".

File: termcap,  Node: Data Base,  Next: Capabilities,  Prev: Library,  Up: Top

The Format of the Data Base

The termcap data base of terminal descriptions is stored in the file
`/etc/termcap'.  It contains terminal descriptions, blank lines, and

A terminal description starts with one or more names for the terminal
type.  The information in the description is a series of "capability
names" and values.  The capability names have standard meanings
(*note Capabilities::.) and their values describe the terminal.

* Menu:

* Format::            Overall format of a terminal description.
* Capability Format:: Format of capabilities within a description.
* Naming::            Naming conventions for terminal types.
* Inheriting::        Inheriting part of a description from
                        a related terminal type.


File: termcap,  Node: Format,  Next: Capability Format,  Prev: Data Base,  Up: Data Base

Terminal Description Format

Aside from comments (lines starting with `#', which are ignored),
each nonblank line in the termcap data base is a terminal description.
A terminal description is nominally a single line, but it can be
split into multiple lines by inserting the two characters `\ newline'.
This sequence is ignored wherever it appears in a description.

The preferred way to split the description is between capabilities:
insert the four characters `: \ newline tab' immediately before any
colon.  This allows each sub-line to start with some indentation. 
This works because, after the `\ newline' are ignored, the result is
`: tab :'; the first colon ends the preceding capability and the
second colon starts the next capability.  If you split with `\
newline' alone, you may not add any indentation after them.

Here is a real example of a terminal description:

     dw|vt52|DEC vt52:\
             :le=^H:bs:cd=\EJ:ce=\EK:cl=\EH\EJ:cm=\EY%+ %+ :co#80:li#24:\

Each terminal description begins with several names for the terminal
type.  The names are separated by `|' characters, and a colon ends
the last name.  The first name should be two characters long; it
exists only for the sake of very old Unix systems and is never used
in modern systems.  The last name should be a fully verbose name such
as "DEC vt52" or "Ann Arbor Ambassador with 48 lines".  The other
names should include whatever the user ought to be able to specify to
get this terminal type, such as `vt52' or `aaa-48'.  *Note Naming::,
for information on how to choose terminal type names.

After the terminal type names come the terminal capabilities,
separated by colons and with a colon after the last one.  Each
capability has a two-letter name, such as `cm' for "cursor motion
string" or `li' for "number of display lines".

File: termcap,  Node: Capability Format,  Next: Naming,  Prev: Format,  Up: Data Base

Writing the Capabilities

There are three kinds of capabilities: flags, numbers, and strings. 
Each kind has its own way of being written in the description.  Each
defined capability has by convention a particular kind of value; for
example, `li' always has a numeric value and `cm' always a string

A flag capability is thought of as having a boolean value: the value
is true if the capability is present, false if not.  When the
capability is present, just write its name between two colons.

A numeric capability has a value which is a nonnegative number. 
Write the capability name, a `#', and the number, between two colons.
For example, `...:li#48:...' is how you specify the `li' capability
for 48 lines.

A string-valued capability has a value which is a sequence of
characters.  Usually these are the characters used to perform some
display operation.  Write the capability name, a `=', and the
characters of the value, between two colons.  For example,
`...:cm=\E[%i%d;%dH:...' is how the cursor motion command for a
standard ANSI terminal would be specified.

Special characters in the string value can be expressed using
`\'-escape sequences as in C; in addition, `\E' stands for ESC.  `^'
is also a kind of escape character; `^' followed by CHAR stands for
the control-equivalent of CHAR.  Thus, `^a' stands for the character
control-a, just like `\001'.  `\' and `^' themselves can be
represented as `\\' and `\^'.

To include a colon in the string, you must write `\072'.  You might
ask, "Why can't `\:' be used to represent a colon?"  The reason is
that the interrogation functions do not count slashes while looking
for a capability.  Even if `:ce=ab\:cd:' were interpreted as giving
the `ce' capability the value `ab:cd', it would also appear to define
`cd' as a flag.

The string value will often contain digits at the front to specify
padding (*note Padding::.) and/or `%'-sequences within to specify how
to encode parameters (*note Parameters::.).  Although these things
are not to be output literally to the terminal, they are considered
part of the value of the capability.  They are special only when the
string value is processed by `tputs', `tparam' or `tgoto'.  By
contrast, `\' and `^' are considered part of the syntax for
specifying the characters in the string.

Let's look at the VT52 example again:

     dw|vt52|DEC vt52:\
             :le=^H:bs:cd=\EJ:ce=\EK:cl=\EH\EJ:cm=\EY%+ %+ :co#80:li#24:\

Here we see the numeric-valued capabilities `co' and `li', the flags
`bs' and `pt', and many string-valued capabilities.  Most of the
strings start with ESC represented as `\E'.  The rest contain control
characters represented using `^'.  The meanings of the individual
capabilities are defined elsewhere (*note Capabilities::.).

File: termcap,  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

     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:

     Short for "wide".  This is a mode that gives the terminal more
     columns than usual.  This is normally a user option.

     "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.

     "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.

     "No arrows".  This terminal description initializes the terminal
     to keep its arrow keys in local mode.  This is a user option.

     "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.

     "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.

     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.

     Says that the terminal has NPAGES pages worth of screen memory,
     for terminals where this is a hardware option.

     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,  Node: Inheriting,  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:\

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:\