TELNET(1C) TELNET(1C)
NAME
telnet - user interface to the TELNET protocol
SYNOPSIS
telnet [ host [ port ] ]
DESCRIPTION
Telnet is used to communicate with another host using the
TELNET protocol. 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 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
immediately 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
"^]"). 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 host [ port ]
Open a connection to the named host. If no port number
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is specified, telnet will attempt to contact a TELNET
server at the default port. The host specification may
be either a host name (see hosts(5)) or an Internet
address specified in the "dot notation" (see inet(3N)).
close
Close a TELNET session and return to command mode.
quit
Close any open TELNET session and exit telnet. An end
of file (in command mode) will also close a session and
exit.
z
Suspend telnet. This command only works when the user
is using the csh(1).
mode type
Type is either line (for "line by line" mode) or
character (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... ]
Displays all, or some, of the set and toggle values
(see below).
? [ command ]
Get help. With no arguments, telnet prints a help
summary. If a command is specified, telnet will print
the help information for just that command.
send arguments
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):
escape
Sends the current telnet escape character
(initially "^]").
synch
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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remote system is a 4.2 BSD system -- if it doesn't
work, a lower case "r" may be echoed on the
terminal).
brk
Sends the TELNET BRK (Break) sequence, which may
have significance to the remote system.
ip
Sends 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
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"line by line" mode, toggles between doing local
echoing of entered characters (for normal
processing), and suppressing echoing of entered
characters (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
localchars 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
localchars 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
localchars 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
localchars below), and if telnet is operating in
"character 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
localchars below), and if telnet is operating in
"character 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.
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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
character is taken to be the terminal's eof
character.
toggle arguments...
Toggle (between TRUE and FALSE) various flags that
control 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
(hopefully) 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
recognized (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(1)).
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 carriage return mode. When this mode is
enabled, most carriage return characters received
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from the remote host will be mapped into a
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.
debug
Toggles socket level debugging (useful only to the
superuser). The initial value for this toggle is
FALSE.
options
Toggles the display of some internal telnet
protocol processing (having to do with TELNET
options). The initial value for this toggle is
FALSE.
netdata
Toggles the display of all network data (in
hexadecimal format). The initial value for this
toggle 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 .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.
ORIGIN
4.3 BSD
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