2.11BSD/man/cat1/telnet.0
TELNET(1C) UNIX Programmer's Manual TELNET(1C)
NAME
telnet - user interface to the TELNET protocol
SYNOPSIS
telnet [ host [ port ] ]
DESCRIPTION
_T_e_l_n_e_t is used to communicate with another host using the
TELNET protocol. If _t_e_l_n_e_t is invoked without arguments, it
enters command mode, indicated by its prompt ("telnet>").
In this mode, it accepts and executes the commands listed
below. If it is invoked with arguments, it performs an open
command (see below) with those arguments.
Once a connection has been opened, _t_e_l_n_e_t enters an input
mode. The input mode entered will be either "character at a
time" or "line by line" depending on what the remote system
supports.
In "character at a time" mode, most text typed is immedi-
ately sent to the remote host for processing.
In "line by line" mode, all text is echoed locally, and
(normally) only completed lines are sent to the remote host.
The "local echo character" (initially "^E") may be used to
turn off and on the local echo (this would mostly be used to
enter passwords without the password being echoed).
In either mode, if the _l_o_c_a_l_c_h_a_r_s toggle is TRUE (the
default in line mode; see below), the user's _q_u_i_t, _i_n_t_r, and
_f_l_u_s_h characters are trapped locally, and sent as TELNET
protocol sequences to the remote side. There are options
(see toggle _a_u_t_o_f_l_u_s_h and toggle _a_u_t_o_s_y_n_c_h below) which
cause this action to flush subsequent output to the terminal
(until the remote host acknowledges the TELNET sequence) and
flush previous terminal input (in the case of _q_u_i_t and
_i_n_t_r).
While connected to a remote host, _t_e_l_n_e_t command mode may be
entered by typing the _t_e_l_n_e_t "escape character" (initially
"^]"). When in command mode, the normal terminal editing
conventions are available.
COMMANDS
The following commands are available. Only enough of each
command to uniquely identify it need be typed (this is also
true for arguments to the mode, set, toggle, and display
commands).
open _h_o_s_t [ _p_o_r_t ]
Open a connection to the named host. If no port number
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TELNET(1C) UNIX Programmer's Manual TELNET(1C)
is specified, _t_e_l_n_e_t will attempt to contact a TELNET
server at the default port. The host specification may
be either a host name (see _h_o_s_t_s(5)) or an Internet
address specified in the "dot notation" (see _i_n_e_t(3N)).
close
Close a TELNET session and return to command mode.
quit
Close any open TELNET session and exit _t_e_l_n_e_t. An end
of file (in command mode) will also close a session and
exit.
z
Suspend _t_e_l_n_e_t. This command only works when the user
is using the _c_s_h(1).
mode _t_y_p_e
_T_y_p_e is either _l_i_n_e (for "line by line" mode) or _c_h_a_r_-
_a_c_t_e_r (for "character at a time" mode). The remote
host is asked for permission to go into the requested
mode. If the remote host is capable of entering that
mode, the requested mode will be entered.
status
Show the current status of _t_e_l_n_e_t. This includes the
peer one is connected to, as well as the current mode.
display [ _a_r_g_u_m_e_n_t... ]
Displays all, or some, of the set and toggle values
(see below).
? [ _c_o_m_m_a_n_d ]
Get help. With no arguments, _t_e_l_n_e_t prints a help sum-
mary. If a command is specified, _t_e_l_n_e_t will print the
help information for just that command.
send _a_r_g_u_m_e_n_t_s
Sends one or more special character sequences to the
remote host. The following are the arguments which may
be specified (more than one argument may be specified
at a time):
_e_s_c_a_p_e
Sends the current _t_e_l_n_e_t escape character (ini-
tially "^]").
_s_y_n_c_h
Sends the TELNET SYNCH sequence. This sequence
causes the remote system to discard all previously
typed (but not yet read) input. This sequence is
sent as TCP urgent data (and may not work if the
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TELNET(1C) UNIX Programmer's Manual TELNET(1C)
remote system is a 4.2 BSD system -- if it doesn't
work, a lower case "r" may be echoed on the termi-
nal).
_b_r_k
Sends the TELNET BRK (Break) sequence, which may
have significance to the remote system.
_i_p
Sends the TELNET IP (Interrupt Process) sequence,
which should cause the remote system to abort the
currently running process.
_a_o
Sends the TELNET AO (Abort Output) sequence, which
should cause the remote system to flush all output
from the remote system to the user's terminal.
_a_y_t
Sends the TELNET AYT (Are You There) sequence, to
which the remote system may or may not choose to
respond.
_e_c
Sends the TELNET EC (Erase Character) sequence,
which should cause the remote system to erase the
last character entered.
_e_l
Sends the TELNET EL (Erase Line) sequence, which
should cause the remote system to erase the line
currently being entered.
_g_a
Sends the TELNET GA (Go Ahead) sequence, which
likely has no significance to the remote system.
_n_o_p
Sends the TELNET NOP (No OPeration) sequence.
?
Prints out help information for the send command.
set _a_r_g_u_m_e_n_t _v_a_l_u_e
Set any one of a number of _t_e_l_n_e_t variables to a
specific value. The special value "off" turns off the
function associated with the variable. The values of
variables may be interrogated with the display command.
The variables which may be specified are:
_e_c_h_o
This is the value (initially "^E") which, when in
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"line by line" mode, toggles between doing local
echoing of entered characters (for normal process-
ing), and suppressing echoing of entered charac-
ters (for entering, say, a password).
_e_s_c_a_p_e
This is the _t_e_l_n_e_t escape character (initially
"^[") which causes entry into _t_e_l_n_e_t command mode
(when connected to a remote system).
_i_n_t_e_r_r_u_p_t
If _t_e_l_n_e_t is in _l_o_c_a_l_c_h_a_r_s mode (see toggle _l_o_c_a_l_-
_c_h_a_r_s below) and the _i_n_t_e_r_r_u_p_t character is typed,
a TELNET IP sequence (see send _i_p above) is sent
to the remote host. The initial value for the
interrupt character is taken to be the terminal's
intr character.
_q_u_i_t
If _t_e_l_n_e_t is in _l_o_c_a_l_c_h_a_r_s mode (see toggle _l_o_c_a_l_-
_c_h_a_r_s below) and the _q_u_i_t character is typed, a
TELNET BRK sequence (see send _b_r_k above) is sent
to the remote host. The initial value for the
quit character is taken to be the terminal's quit
character.
_f_l_u_s_h_o_u_t_p_u_t
If _t_e_l_n_e_t is in _l_o_c_a_l_c_h_a_r_s mode (see toggle _l_o_c_a_l_-
_c_h_a_r_s below) and the _f_l_u_s_h_o_u_t_p_u_t character is
typed, a TELNET AO sequence (see send _a_o above) is
sent to the remote host. The initial value for
the flush character is taken to be the terminal's
flush character.
_e_r_a_s_e
If _t_e_l_n_e_t is in _l_o_c_a_l_c_h_a_r_s mode (see toggle _l_o_c_a_l_-
_c_h_a_r_s below), and if _t_e_l_n_e_t is operating in "char-
acter at a time" mode, then when this character is
typed, a TELNET EC sequence (see send _e_c above) is
sent to the remote system. The initial value for
the erase character is taken to be the terminal's
erase character.
_k_i_l_l
If _t_e_l_n_e_t is in _l_o_c_a_l_c_h_a_r_s mode (see toggle _l_o_c_a_l_-
_c_h_a_r_s below), and if _t_e_l_n_e_t is operating in "char-
acter at a time" mode, then when this character is
typed, a TELNET EL sequence (see send _e_l above) is
sent to the remote system. The initial value for
the kill character is taken to be the terminal's
kill character.
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_e_o_f
If _t_e_l_n_e_t is operating in "line by line" mode,
entering this character as the first character on
a line will cause this character to be sent to the
remote system. The initial value of the eof char-
acter is taken to be the terminal's eof character.
toggle _a_r_g_u_m_e_n_t_s...
Toggle (between TRUE and FALSE) various flags that con-
trol how _t_e_l_n_e_t responds to events. More than one
argument may be specified. The state of these flags
may be interrogated with the display command. Valid
arguments are:
_l_o_c_a_l_c_h_a_r_s
If this is TRUE, then the _f_l_u_s_h, _i_n_t_e_r_r_u_p_t, _q_u_i_t,
_e_r_a_s_e, and _k_i_l_l characters (see set above) are
recognized locally, and transformed into (hope-
fully) appropriate TELNET control sequences
(respectively _a_o, _i_p, _b_r_k, _e_c, and _e_l; see send
above). The initial value for this toggle is TRUE
in "line by line" mode, and FALSE in "character at
a time" mode.
_a_u_t_o_f_l_u_s_h
If _a_u_t_o_f_l_u_s_h and _l_o_c_a_l_c_h_a_r_s are both TRUE, then
when the _a_o, _i_n_t_r, or _q_u_i_t characters are recog-
nized (and transformed into TELNET sequences; see
set above for details), _t_e_l_n_e_t refuses to display
any data on the user's terminal until the remote
system acknowledges (via a TELNET _T_i_m_i_n_g _M_a_r_k
option) that it has processed those TELNET
sequences. The initial value for this toggle is
TRUE if the terminal user had not done an "stty
noflsh", otherwise FALSE (see _s_t_t_y(_1)).
_a_u_t_o_s_y_n_c_h
If _a_u_t_o_s_y_n_c_h and _l_o_c_a_l_c_h_a_r_s are both TRUE, then
when either the _i_n_t_r or _q_u_i_t characters is typed
(see set above for descriptions of the _i_n_t_r and
_q_u_i_t characters), the resulting TELNET sequence
sent is followed by the TELNET SYNCH sequence.
This procedure should cause the remote system to
begin throwing away all previously typed input
until both of the TELNET sequences have been read
and acted upon. The initial value of this toggle
is FALSE.
_c_r_m_o_d
Toggle carriage return mode. When this mode is
enabled, most carriage return characters received
from the remote host will be mapped into a
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TELNET(1C) UNIX Programmer's Manual TELNET(1C)
carriage return followed by a line feed. This
mode does not affect those characters typed by the
user, only those received from the remote host.
This mode is not very useful unless the remote
host only sends carriage return, but never line
feed. The initial value for this toggle is FALSE.
_d_e_b_u_g
Toggles socket level debugging (useful only to the
_s_u_p_e_ruser). The initial value for this toggle is
FALSE.
_o_p_t_i_o_n_s
Toggles the display of some internal _t_e_l_n_e_t proto-
col processing (having to do with TELNET options).
The initial value for this toggle is FALSE.
_n_e_t_d_a_t_a
Toggles the display of all network data (in hexa-
decimal format). The initial value for this tog-
gle is FALSE.
?
Displays the legal toggle commands.
BUGS
There is no adequate way for dealing with flow control.
On some remote systems, echo has to be turned off manually
when in "line by line" mode.
There is enough settable state to justify a ._t_e_l_n_e_t_r_c file.
No capability for a ._t_e_l_n_e_t_r_c file is provided.
In "line by line" mode, the terminal's _e_o_f character is only
recognized (and sent to the remote system) when it is the
first character on a line.
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