telnet(1c)telnet(1c)Nametelnet - user interface to the TELNET protocol
Syntaxtelnet [host[port]]
Description
The interface is used to communicate with another host using the TELNET
protocol. If is invoked without arguments, it enters command mode,
which is indicated by the prompt, telnet>. In this mode, 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 is opened, enters input mode. The input mode is
either character-at-a-time or line-by-line, depending on what the
remote system supports. In character-at-a-time mode, text is sent to
the remote host as it is typed. In line-by-line mode, text is echoed
locally and only completed lines are sent to the remote host. The
local-echo-character, initially ^E. turns the local echo on and off,
which is useful when you want to enter passwords without them echoing
to the screen.
In either mode, if the localchars toggle is TRUE (the default in line
mode), then the user's quit, intr, and flush characters are trapped
locally and sent as TELNET protocol sequences to the remote side.
Options such as toggle autoflush and toggle autosynch flush previous
terminal input, as in quit and intr, in addition to flushing subsequent
output to the terminal until the remote host acknowledges the TELNET
sequence.
To issue commands when in input mode, precede them with the escape
character, initially the control character followed by a right bracket
(^]). When in command mode, use the normal terminal editing conven‐
tions.
The following commands are available:
open host [ port ]
Opens a connection to the named host. If no port number
is specified, attempts 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. For further information, see and
close Closes a TELNET session and returns to command mode.
quit Closes any open TELNET session and exits
z Suspends This command only works when the user is using
the
mode type The type is either line, for line-by-line mode, or char‐
acter, for character-at-a-time mode. The local host
asks the remote host for permission to go into one or
the other mode. The remote host enters the requested
mode if it is capable of it.
status Shows the current status of This includes the peer one
is connected to, as well as the state of debugging.
display [ argument... ]
Displays all, or some, of the set and toggle values (see
below).
? [ command ]
Accesses on-line help. With no arguments, prints a help
summary. If a command is specified, prints the help
information for that command.
send argument(s)
Sends one or more special character sequences to the
remote host. One or more of the following arguments can
be specified:
escape
Sends the current escape character (initially the
control character followed by a right bracket,
^]).
synch
Sends the TELNET SYNCH sequence. This sequence
causes the remote system to discard input that
was previously entered but that it has not yet
read. 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 screen.
brk
Sends the TELNET BRK (Break) sequence, which may
have significance to the remote system.
ip
Sends the TELNET IP (Interrupt Process) sequence,
which causes the remote system to abort the cur‐
rently running process.
ao
Sends the TELNET AO (Abort Output) sequence,
which causes the remote system to flush all out‐
put from the remote system to the user's termi‐
nal.
ayt
Sends the TELNET AYT (Are You There) sequence.
The remote system may or may not respond.
ec
Sends the TELNET EC (Erase Character) sequence,
which causes the remote system to erase the last
character entered.
el
Sends the TELNET EL (Erase Line) sequence, which
causes the remote system to erase the line cur‐
rently being entered.
ga
Sends the TELNET GA (Go Ahead) sequence. Often
this sequence 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
Sets a variable to a specific value. The off value
turns off the function associated with the variable.
The current values of variables can be displayed with
the display command.
The following variables that can be specified:
echo
Toggles between local echoing of entered characters, and
suppressing echoing of entered characters when in line-
by-line mode. The value is initially ^E.
escape
Enters the command mode when you are connected to a
remote system. The value is initially the control char‐
acter followed by a left bracket (^[).
interrupt
Sends a TELNET IP sequence (see send ip above) to the
remote host if is in localchars mode (see toggle
localchars below) and the interrupt character is typed.
The initial value for the interrupt character is the ter‐
minal's intr character.
quit
Sends a TELNET BRK sequence (see send brk above) to the
remote host if is in localchars mode (see toggle
localchars below) and the quit character is typed. The
initial value for the quit character is the terminal's
quit character.
flushoutput
Sends a TELNET AO sequence (see send ao above) to the
remote host if telnet is in localchars mode (see toggle
localchars below) and the flushoutput character is typed.
The initial value for the flush character is the termi‐
nal's flush character.
erase
Sends a TELNET EC sequence (see send ec above) to the
remote system if telnet is in localchars mode (see toggle
localchars below), and if telnet is operating in charac‐
ter-at-time mode. The initial value for the erase char‐
acter is the terminal's erase character.
kill
Sends a TELNET EL sequence (see send el above) to the
remote system if is in localchars mode (see toggle
localchars below) and if is operating in character-at-a-
time mode. The initial value for the kill character is
the terminal's kill character.
eof
Sends this character to the remote system if is operating
in line-by-line mode and this character is entered as the
first character on a line. The initial value of the eof
character is the terminal's eof character.
toggle arguments...
Toggles (between TRUE and FALSE) flags that control how responds
to events. More than one argument may be specified and the cur‐
rent value of these flags can be displayed with the display com‐
mand. Valid arguments for the command are the following:
localchars
Causes the flush, interrupt, quit, erase, and kill char‐
acters to be recognized locally and transformed into
appropriate TELNET control sequences if this flag is set
to TRUE. (See set above). The appropriate TELNET con‐
trol sequences are: ao, ip, brk, ec, and el, respec‐
tively. For more information see the command. The ini‐
tial value for this toggle is TRUE in line-by-line mode,
and FALSE in character-at-a-time mode.
autoflush
Causes the command to not display any data on the user's
terminal until the remote system acknowledges (via a TEL‐
NET Timing Mark option) that it recognized and processed
the following TELNET sequences: ao, intr, or quit. Both
autoflush and localchars must be TRUE for autoflush to
work in this manner. The initial value for this toggle
is TRUE if the terminal user did not specify Otherwise it
is FALSE. For further information, see
autosynch
Causes the TELNET SYNCH sequence to follow the TELNET
sequence that is initiated when either the intr or quit
character is typed. The autosynch flag works in this
manner when both the autosynch and localchars are TRUE.
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
Toggles carriage return mode. When this mode is enabled,
most carriage return characters received from the remote
host are mapped into a carriage return followed by a line
feed. It is useful only when the remote host sends car‐
riage returns but never line feeds. The initial value
for this toggle is FALSE.
debug
Toggles socket level debugging which is useful only to
the superuser. The initial value for this toggle is
FALSE.
options
Toggles the display of internal protocol processing that
deals 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.
Restrictions
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.
telnet(1c)
