terminal.texi

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This specifies eight bits per byte.
@end deftypevr

The following four bits are BSD extensions; this exist only on BSD
systems and the GNU system.

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CCTS_OFLOW
If this bit is set, enable flow control of output based on the CTS wire
(RS232 protocol).
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CRTS_IFLOW
If this bit is set, enable flow control of input based on the RTS wire
(RS232 protocol).
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t MDMBUF
If this bit is set, enable carrier-based flow control of output.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t CIGNORE
If this bit is set, it says to ignore the control modes and line speed
values entirely.  This is only meaningful in a call to @code{tcsetattr}.

The @code{c_cflag} member and the line speed values returned by
@code{cfgetispeed} and @code{cfgetospeed} will be unaffected by the
call.  @code{CIGNORE} is useful if you want to set all the software
modes in the other members, but leave the hardware details in
@code{c_cflag} unchanged.  (This is how the @code{TCSASOFT} flag to
@code{tcsettattr} works.)

This bit is never set in the structure filled in by @code{tcgetattr}.
@end deftypevr

@node Local Modes
@subsection Local Modes

This section describes the flags for the @code{c_lflag} member of the
@code{struct termios} structure.  These flags generally control
higher-level aspects of input processing than the input modes flags
described in @ref{Input Modes}, such as echoing, signals, and the choice
of canonical or noncanonical input.

The @code{c_lflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}.  Don't
try to specify the entire value for @code{c_lflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ICANON
This bit, if set, enables canonical input processing mode.  Otherwise,
input is processed in noncanonical mode.  @xref{Canonical or Not}.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHO
If this bit is set, echoing of input characters back to the terminal
is enabled.
@cindex echo of terminal input
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHOE
If this bit is set, echoing indicates erasure of input with the ERASE
character by erasing the last character in the current line from the
screen.  Otherwise, the character erased is re-echoed to show what has
happened (suitable for a printing terminal).

This bit only controls the display behavior; the @code{ICANON} bit by
itself controls actual recognition of the ERASE character and erasure of
input, without which @code{ECHOE} is simply irrelevant.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOPRT
This bit is like @code{ECHOE}, enables display of the ERASE character in
a way that is geared to a hardcopy terminal.  When you type the ERASE
character, a @samp{\} character is printed followed by the first
character erased.  Typing the ERASE character again just prints the next
character erased.  Then, the next time you type a normal character, a
@samp{/} character is printed before the character echoes.

This is a BSD extension, and exists only in BSD systems and the
GNU system.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHOK
This bit enables special display of the KILL character by moving to a
new line after echoing the KILL character normally.  The behavior of
@code{ECHOKE} (below) is nicer to look at.

If this bit is not set, the KILL character echoes just as it would if it
were not the KILL character.  Then it is up to the user to remember that
the KILL character has erased the preceding input; there is no
indication of this on the screen.

This bit only controls the display behavior; the @code{ICANON} bit by
itself controls actual recognition of the KILL character and erasure of
input, without which @code{ECHOK} is simply irrelevant.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOKE
This bit is similar to @code{ECHOK}.  It enables special display of the
KILL character by erasing on the screen the entire line that has been
killed.  This is a BSD extension, and exists only in BSD systems and the
GNU system.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ECHONL
If this bit is set and the @code{ICANON} bit is also set, then the
newline (@code{'\n'}) character is echoed even if the @code{ECHO} bit
is not set.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ECHOCTL
If this bit is set and the @code{ECHO} bit is also set, echo control
characters with @samp{^} followed by the corresponding text character.
Thus, control-A echoes as @samp{^A}.  This is usually the preferred mode
for interactive input, because echoing a control character back to the
terminal could have some undesired effect on the terminal.

This is a BSD extension, and exists only in BSD systems and the
GNU system.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ISIG
This bit controls whether the INTR, QUIT, and SUSP characters are
recognized.  The functions associated with these characters are performed
if and only if this bit is set.  Being in canonical or noncanonical
input mode has no affect on the interpretation of these characters.

You should use caution when disabling recognition of these characters.
Programs that cannot be interrupted interactively are very
user-unfriendly.  If you clear this bit, your program should provide
some alternate interface that allows the user to interactively send the
signals associated with these characters, or to escape from the program.
@cindex interactive signals, from terminal

@xref{Signal Characters}.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IEXTEN
POSIX.1 gives @code{IEXTEN} implementation-defined meaning,
so you cannot rely on this interpretation on all systems.

On BSD systems and the GNU system, it enables the LNEXT and DISCARD characters.
@xref{Other Special}.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t NOFLSH
Normally, the INTR, QUIT, and SUSP characters cause input and output
queues for the terminal to be cleared.  If this bit is set, the queues
are not cleared.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t TOSTOP
If this bit is set and the system supports job control, then
@code{SIGTTOU} signals are generated by background processes that
attempt to write to the terminal.  @xref{Access to the Terminal}.
@end deftypevr

The following bits are BSD extensions; they exist only in BSD systems
and the GNU system.
     
@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ALTWERASE
This bit determines how far the WERASE character should erase.  The
WERASE character erases back to the beginning of a word; the question
is, where do words begin?

If this bit is clear, then the beginning of a word is a nonwhitespace
character following a whitespace character.  If the bit is set, then the
beginning of a word is an alphanumeric character or underscore following
a character which is none of those.

@xref{Editing Characters}, for more information about the WERASE character.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t FLUSHO
This is the bit that toggles when the user types the DISCARD character.
While this bit is set, all output is discarded.  @xref{Other Special}.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t NOKERNINFO
Setting this bit disables handling of the STATUS character.
@xref{Other Special}.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t PENDIN
If this bit is set, it indicates that there is a line of input that
needs to be reprinted.  Typing the REPRINT character sets this bit; the
bit remains set until reprinting is finished.  @xref{Editing Characters}.
@end deftypevr

@c EXTPROC is too obscure to document now.  --roland

@node Line Speed
@subsection Line Speed
@cindex line speed
@cindex baud rate
@cindex terminal line speed
@cindex terminal line speed

The terminal line speed tells the computer how fast to read and write
data on the terminal.

If the terminal is connected to a real serial line, the terminal speed
you specify actually controls the line---if it doesn't match the
terminal's own idea of the speed, communication does not work.  Real
serial ports accept only certain standard speeds.  Also, particular
hardware may not support even all the standard speeds.  Specifying a
speed of zero hangs up a dialup connection and turns off modem control
signals.

If the terminal is not a real serial line (for example, if it is a
network connection), then the line speed won't really affect data
transmission speed, but some programs will use it to determine the
amount of padding needed.  It's best to specify a line speed value that
matches the actual speed of the actual terminal, but you can safely
experiment with different values to vary the amount of padding.

There are actually two line speeds for each terminal, one for input and
one for output.  You can set them independently, but most often
terminals use the same speed for both directions.

The speed values are stored in the @code{struct termios} structure, but
don't try to access them in the @code{struct termios} structure
directly.  Instead, you should use the following functions to read and
store them:

@comment termios.h
@comment POSIX.1
@deftypefun speed_t cfgetospeed (const struct termios *@var{termios-p})
This function returns the output line speed stored in the structure
@code{*@var{termios-p}}.
@end deftypefun

@comment termios.h
@comment POSIX.1
@deftypefun speed_t cfgetispeed (const struct termios *@var{termios-p})
This function returns the input line speed stored in the structure
@code{*@var{termios-p}}.
@end deftypefun

@comment termios.h
@comment POSIX.1
@deftypefun int cfsetospeed (struct termios *@var{termios-p}, speed_t @var{speed})
This function stores @var{speed} in @code{*@var{termios-p}} as the output
speed.  The normal return value is @code{0}; a value of @code{-1}
indicates an error.  If @var{speed} is not a speed, @code{cfsetospeed}
returns @code{-1}.
@end deftypefun

@comment termios.h
@comment POSIX.1
@deftypefun int cfsetispeed (struct termios *@var{termios-p}, speed_t @var{speed})
This function stores @var{speed} in @code{*@var{termios-p}} as the input
speed.  The normal return value is @code{0}; a value of @code{-1}
indicates an error.  If @var{speed} is not a speed, @code{cfsetospeed}
returns @code{-1}.
@end deftypefun

@comment termios.h
@comment BSD
@deftypefun int cfsetspeed (struct termios *@var{termios-p}, speed_t @var{speed})
This function stores @var{speed} in @code{*@var{termios-p}} as both the
input and output speeds.  The normal return value is @code{0}; a value
of @code{-1} indicates an error.  If @var{speed} is not a speed,
@code{cfsetspeed} returns @code{-1}.  This function is an extension in
4.4 BSD.
@end deftypefun

@comment termios.h
@comment POSIX.1
@deftp {Data Type} speed_t
The @code{speed_t} type is an unsigned integer data type used to
represent line speeds.
@end deftp

The functions @code{cfsetospeed} and @code{cfsetispeed} report errors
only for speed values that the system simply cannot handle.  If you
specify a speed value that is basically acceptable, then those functions
will succeed.  But they do not check that a particular hardware device
can actually support the specified speeds---in fact, they don't know
which device you plan to set the speed for.  If you use @code{tcsetattr}
to set the speed of a particular device to a value that it cannot
handle, @code{tcsetattr} returns @code{-1}.

@strong{Portability note:} In the GNU library, the functions above
accept speeds measured in bits per second as input, and return speed
values measured in bits per second.  Other libraries require speeds to
be indicated by special codes.  For POSIX.1 portability, you must use
one of the following symbols to represent the speed; their precise
numeric values are system-dependent, but each name has a fixed meaning:
@code{B110} stands for 110 bps, @code{B300} for 300 bps, and so on.
There is no portable way to represent any speed but these, but these are
the only speeds that typical serial lines can support.

@comment termios.h
@comment POSIX.1
@vindex B0
@comment termios.h
@comment POSIX.1
@vindex B50
@comment termios.h
@comment POSIX.1
@vindex B75
@comment termios.h
@comment POSIX.1
@vindex B110
@comment termios.h
@comment POSIX.1
@vindex B134
@comment termios.h
@comment POSIX.1
@vindex B150
@comment termios.h
@comment POSIX.1
@vindex B200
@comment termios.h
@comment POSIX.1
@vindex B300