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telnet.man
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TELNET(1C) USER COMMANDS TELNET(1C)
NAME
telnet - user interface to a remote system using the TELNET
protocol
DESCRIPTION
telnet communicates with another host using the TELNET pro-
tocol. If telnet 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, telnet enters input mode.
In this mode, text typed is sent to the remote host. 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 localchars toggle is TRUE (the
default in line mode; see below), the user's quit, intr, and
flush characters are trapped locally, and sent as TELNET
protocol sequences to the remote side. There are options
(see toggle autoflush and toggle autosynch 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 quit and
intr).
While connected to a remote host, telnet command mode may be
entered by typing the telnet "escape character" (initially
`^]', (control-right-bracket)). When in command mode, the
normal terminal editing conventions are available.
USAGE
Telnet 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 host [ port ]
Open a connection to the named host. If no port number
is specified, telnet will attempt to contact a TELNET
server at the default port. The host specification may
be either a host name or an Internet address specified
in the "dot notation".
close
Close a TELNET session and return to command mode.
quit Close any open TELNET session and exit telnet. An EOF
(in command mode) will also close a session and exit.
mode type
type is either line (for "line by line" mode) or char-
acter (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 telnet. This includes the
peer one is connected to, as well as the current mode.
display [ argument... ]
Display all, or some, of the set and toggle values (see
below).
? [ command ]
Get help. With no arguments, telnet prints a help sum-
mary. If a command is specified, telnet will print the
help information for just that command.
^d
Send control-d to the host.
send arguments
Send 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):
escape
Send the current telnet escape character (ini-
tially `^]').
synch
Send 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
remote system is a 4.2 BSD system -- if it does
not work, a lower case "r" may be echoed on the
terminal).
brk Send the TELNET BRK (Break) sequence, which may
have significance to the remote system.
ip Send the TELNET IP (Interrupt Process) sequence,
which should cause the remote system to abort the
currently running process.
ao 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.
ayt Sends the TELNET AYT (Are You There) sequence, to
which the remote system may or may not choose to
respond.
ec Sends the TELNET EC (Erase Character) sequence,
which should cause the remote system to erase the
last character entered.
el Sends the TELNET EL (Erase Line) sequence, which
should cause the remote system to erase the line
currently being entered.
ga Sends the TELNET GA (Go Ahead) sequence, which
likely has no significance to the remote system.
nop Sends the TELNET NOP (No Operation) sequence.
? Prints out help information for the send command.
set argument value
Set any one of a number of telnet 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:
echo This is the value (initially `^E') which, when in
"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).
escape
This is the telnet escape character (initially
`^[') which causes entry into telnet command mode
(when connected to a remote system).
interrupt
If telnet is in localchars mode (see toggle local-
chars below) and the interrupt character is typed,
a TELNET IP sequence (see send ip above) is sent
to the remote host. The initial value for the
interrupt character is taken to be the terminal's
intr character.
quit If telnet is in localchars mode (see toggle local-
chars below) and the quit character is typed, a
TELNET BRK sequence (see send brk above) is sent
to the remote host. The initial value for the
quit character is taken to be the terminal's quit
character.
flushoutput
If telnet is in localchars mode (see toggle local-
chars below) and the flushoutput character is
typed, a TELNET AO sequence (see send ao above) is
sent to the remote host. The initial value for
the flush character is taken to be the terminal's
flush character.
erase
If telnet is in localchars mode (see toggle local-
chars below), and if telnet is operating in "char-
acter at a time" mode, then when this character is
typed, a TELNET EC sequence (see send ec above) is
sent to the remote system. The initial value for
the erase character is taken to be the terminal's
erase character.
kill If telnet is in localchars mode (see toggle local-
chars below), and if telnet is operating in "char-
acter at a time" mode, then when this character is
typed, a TELNET EL sequence (see send el above) is
sent to the remote system. The initial value for
the kill character is taken to be the terminal's
kill character.
eof If telnet 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 arguments...
Toggle (between TRUE and FALSE) various flags that con-
trol how telnet 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:
localchars
If this is TRUE, then the flush, interrupt, quit,
erase, and kill characters (see set above) are
recognized locally, and transformed into (hope-
fully) appropriate TELNET control sequences
(respectively ao, ip, brk, ec, and el; see send
above). The initial value for this toggle is TRUE
in "line by line" mode, and FALSE in "character at
a time" mode.
autoflush
If autoflush and localchars are both TRUE, then
when the ao, intr, or quit characters are recog-
nized (and transformed into TELNET sequences; see
set above for details), telnet refuses to display
any data on the user's terminal until the remote
system acknowledges (via a TELNET Timing Mark
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 stty(1V)).
autosynch
If autosynch and localchars are both TRUE, then
when either the intr or quit characters is typed
(see set above for descriptions of the intr and
quit 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.
crmod
Toggle RETURN mode. When this mode is enabled,
most RETURN characters received from the remote
host will be mapped into a RETURN followed by a
LINEFEED. This mode does not affect those charac-
ters typed by the user, only those received from
the remote host. This mode is not very useful
unless the remote host only sends RETURN, but
never LINEFEED. The initial value for this toggle
is FALSE.
debug
Toggle socket level debugging (useful only to the
super-user). The initial value for this toggle is
FALSE.
options
Toggle the display of some internal telnet proto-
col processing (having to do with TELNET options).
The initial value for this toggle is FALSE.
netdata
Toggle the display of all network data (in hexade-
cimal format). The initial value for this toggle
is FALSE.
? Display 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 .telnetrc file.
No capability for a .telnetrc file is provided.
In "line by line" mode, the terminal's EOF character is only
recognized (and sent to the remote system) when it is the
first character on a line.