4.4BSD/usr/share/man/cat1/telnet.0
TELNET(1) BSD Reference Manual TELNET(1)
NNAAMMEE
tteellnneett - user interface to the TELNET protocol
SSYYNNOOPPSSIISS
tteellnneett [--dd] [--aa] [--nn _t_r_a_c_e_f_i_l_e] [--ee _e_s_c_a_p_e_c_h_a_r] [[--ll _u_s_e_r] _h_o_s_t [port]]
DDEESSCCRRIIPPTTIIOONN
The tteellnneett command is used to communicate with another host using the
TELNET protocol. If tteellnneett is invoked without the _h_o_s_t argument, it en-
ters command mode, indicated by its prompt (tteellnneett>>). In this mode, it
accepts and executes the commands listed below. If it is invoked with
arguments, it performs an ooppeenn command with those arguments.
Options:
--dd Sets the initial value of the ddeebbuugg toggle to TRUE
--aa Attempt automatic login. Currently, this sends the user name via
the USER variable of the ENVIRON option if supported by the re-
mote system. The name used is that of the current user as re-
turned by getlogin(2) if it agrees with the current user ID, oth-
erwise it is the name associated with the user ID.
--nn _t_r_a_c_e_f_i_l_e
Opens _t_r_a_c_e_f_i_l_e for recording trace information. See the sseett
ttrraacceeffiillee command below.
--ll _u_s_e_r
When connecting to the remote system, if the remote system under-
stands the ENVIRON option, then _u_s_e_r will be sent to the remote
system as the value for the variable USER. This option implies
the --aa option. This option may also be used with the ooppeenn com-
mand.
--ee _e_s_c_a_p_e _c_h_a_r
Sets the initial tteellnneett tteellnneett escape character to _e_s_c_a_p_e _c_h_a_r_.
If _e_s_c_a_p_e _c_h_a_r is ommitted, then there will be no escape charac-
ter.
_h_o_s_t Indicates the official name, an alias, or the Internet address of
a remote host.
_p_o_r_t Indicates a port number (address of an application). If a number
is not specified, the default tteellnneett port is used.
Once a connection has been opened, tteellnneett will attempt to enable the
TELNET LINEMODE option. If this fails, then tteellnneett will revert to one of
two input modes: either ``character at a time'' or ``old line by line''
depending on what the remote system supports.
When LINEMODE is enabled, character processing is done on the local sys-
tem, under the control of the remote system. When input editing or char-
acter echoing is to be disabled, the remote system will relay that infor-
mation. The remote system will also relay changes to any special charac-
ters that happen on the remote system, so that they can take effect on
the local system.
In ``character at a time'' mode, most text typed is immediately sent to
the remote host for processing.
In ``old line by line'' mode, all text is echoed locally, and (normally)
only completed lines are sent to the remote host. The ``local echo char-
acter'' (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).
If the LINEMODE option is enabled, or if the llooccaallcchhaarrss toggle is TRUE
(the default for ``old line by line``; see below), the user's qquuiitt, iinnttrr,
and fflluusshh characters are trapped locally, and sent as TELNET protocol se-
quences to the remote side. If LINEMODE has ever been enabled, then the
user's ssuusspp and eeooff are also sent as TELNET protocol sequences, and qquuiitt
is sent as a TELNET ABORT instead of BREAK There are options (see ttooggggllee
aauuttoofflluusshh and ttooggggllee aauuttoossyynncchh 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 qquuiitt
and iinnttrr).
While connected to a remote host, tteellnneett command mode may be entered by
typing the tteellnneett ``escape character'' (initially ``^]''). When in com-
mand mode, the normal terminal editing conventions are available.
The following tteellnneett commands are available. Only enough of each command
to uniquely identify it need be typed (this is also true for arguments to
the mmooddee, sseett, ttooggggllee, uunnsseett, ssllcc, eennvviirroonn, and ddiissppllaayy commands).
cclloossee Close a TELNET session and return to command mode.
ddiissppllaayy _a_r_g_u_m_e_n_t _._._.
Displays all, or some, of the sseett and ttooggggllee values (see be-
low).
mmooddee _t_y_p_e _T_y_p_e is one of several options, depending on the state of the
TELNET session. The remote host is asked for permission to go
into the requested mode. If the remote host is capable of en-
tering that mode, the requested mode will be entered.
cchhaarraacctteerr Disable the TELNET LINEMODE option, or, if the
remote side does not understand the LINEMODE op-
tion, then enter ``character at a time`` mode.
lliinnee Enable the TELNET LINEMODE option, or, if the
remote side does not understand the LINEMODE op-
tion, then attempt to enter ``old-line-by-line``
mode.
iissiigg (--iissiigg) Attempt to enable (disable) the TRAPSIG mode of
the LINEMODE option. This requires that the
LINEMODE option be enabled.
eeddiitt (--eeddiitt) Attempt to enable (disable) the EDIT mode of the
LINEMODE option. This requires that the
LINEMODE option be enabled.
ssooffttttaabbss (--ssooffttttaabbss)
Attempt to enable (disable) the SOFT_TAB mode of
the LINEMODE option. This requires that the
LINEMODE option be enabled.
lliitteecchhoo (--lliitteecchhoo)
Attempt to enable (disable) the LIT_ECHO mode of
the LINEMODE option. This requires that the
LINEMODE option be enabled.
?? Prints out help information for the mmooddee com-
mand.
ooppeenn _h_o_s_t [[--ll] _u_s_e_r][--_p_o_r_t]
Open a connection to the named host. If no port number is
specified, tteellnneett 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(3)). The [--ll] option may be used
to specify the user name to be passed to the remote system via
the ENVIRON option. When connecting to a non-standard port,
tteellnneett omits any automatic initiation of TELNET options. When
the port number is preceeded by a minus sign, the inital op-
tion negotiation is done. After establishing a connection,
the file _._t_e_l_n_e_t_r_c in the users home directory is opened.
Lines begining with a # are comment lines. Blank lines are
ignored. Lines that begin without whitespace are the start of
a machine entry. The first thing on the line is the name of
the machine that is being connected to. The rest of the line,
and successive lines that begin with whitespace are assumed to
be tteellnneett commands and are processed as if they had been typed
in manually to the tteellnneett command prompt.
qquuiitt Close any open TELNET session and exit tteellnneett. An end of file
(in command mode) will also close a session and exit.
sseenndd _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):
aabboorrtt Sends the TELNET ABORT (Abort processes) sequence.
aaoo Sends the TELNET AO (Abort Output) sequence, which
should cause the remote system to flush all output
_f_r_o_m the remote system _t_o the user's terminal.
aayytt Sends the TELNET AYT (Are You There) sequence, to
which the remote system may or may not choose to re-
spond.
bbrrkk Sends the TELNET BRK (Break) sequence, which may have
significance to the remote system.
eecc Sends the TELNET EC (Erase Character) sequence, which
should cause the remote system to erase the last char-
acter entered.
eell Sends the TELNET EL (Erase Line) sequence, which
should cause the remote system to erase the line cur-
rently being entered.
eeooff Sends the TELNET EOF (End Of File) sequence.
eeoorr Sends the TELNET EOR (End of Record) sequence.
eessccaappee Sends the current tteellnneett escape character (initially
``^'').
ggaa Sends the TELNET GA (Go Ahead) sequence, which likely
has no significance to the remote system.
ggeettssttaattuuss
If the remote side supports the TELNET STATUS command,
ggeettssttaattuuss will send the subnegotiation to request that
the server send its current option status.
iipp Sends the TELNET IP (Interrupt Process) sequence,
which should cause the remote system to abort the cur-
rently running process.
nnoopp Sends the TELNET NOP (No OPeration) sequence.
ssuusspp Sends the TELNET SUSP (SUSPend process) sequence.
ssyynncchh 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 ur-
gent data (and may not work if the remote system is a
4.2BSD system -- if it doesn't work, a lower case
``r'' may be echoed on the terminal).
?? Prints out help information for the sseenndd command.
sseett _a_r_g_u_m_e_n_t _v_a_l_u_e
uunnsseett _a_r_g_u_m_e_n_t _v_a_l_u_e
The sseett command will set any one of a number of tteellnneett vari-
ables to a specific value or to TRUE. The special value ooffff
turns off the function associated with the variable, this is
equivalent to using the uunnsseett command. The uunnsseett command will
disable or set to FALSE any of the specified functions. The
values of variables may be interrogated with the ddiissppllaayy com-
mand. The variables which may be set or unset, but not tog-
gled, are listed here. In addition, any of the variables for
the ttooggggllee command may be explicitly set or unset using the
sseett and uunnsseett commands.
eecchhoo This is the value (initially ``^E'') which, when in
``line by line'' mode, toggles between doing local
echoing of entered characters (for normal processing),
and suppressing echoing of entered characters (for en-
tering, say, a password).
eeooff If tteellnneett is operating in LINEMODE or ``old 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 eeooff char-
acter.
eerraassee If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee llooccaallcchhaarrss
below), aanndd if tteellnneett is operating in ``character at a
time'' mode, then when this character is typed, a
TELNET EC sequence (see sseenndd eecc above) is sent to the
remote system. The initial value for the erase char-
acter is taken to be the terminal's eerraassee character.
eessccaappee This is the tteellnneett escape character (initially ``^['')
which causes entry into tteellnneett command mode (when con-
nected to a remote system).
fflluusshhoouuttppuutt
If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee llooccaallcchhaarrss
below) and the fflluusshhoouuttppuutt character is typed, a
TELNET AO sequence (see sseenndd aaoo above) is sent to the
remote host. The initial value for the flush charac-
ter is taken to be the terminal's fflluusshh character.
iinntteerrrruupptt
If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee llooccaallcchhaarrss
below) and the iinntteerrrruupptt character is typed, a TELNET
IP sequence (see sseenndd iipp above) is sent to the remote
host. The initial value for the interrupt character
is taken to be the terminal's iinnttrr character.
kkiillll If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee llooccaallcchhaarrss
below), aanndd if tteellnneett is operating in ``character at a
time'' mode, then when this character is typed, a
TELNET EL sequence (see sseenndd eell above) is sent to the
remote system. The initial value for the kill charac-
ter is taken to be the terminal's kkiillll character.
llnneexxtt If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's llnneexxtt character. The initial value for the
lnext character is taken to be the terminal's llnneexxtt
character.
qquuiitt If tteellnneett is in llooccaallcchhaarrss mode (see ttooggggllee llooccaallcchhaarrss
below) and the qquuiitt character is typed, a TELNET BRK
sequence (see sseenndd bbrrkk above) is sent to the remote
host. The initial value for the quit character is
taken to be the terminal's qquuiitt character.
rreepprriinntt
If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's rreepprriinntt character. The initial value for
the reprint character is taken to be the terminal's
rreepprriinntt character.
ssttaarrtt If the TELNET TOGGLE-FLOW-CONTROL option has been en-
abled, then this character is taken to be the termi-
nal's ssttaarrtt character. The initial value for the kill
character is taken to be the terminal's ssttaarrtt charac-
ter.
ssttoopp If the TELNET TOGGLE-FLOW-CONTROL option has been en-
abled, then this character is taken to be the termi-
nal's ssttoopp character. The initial value for the kill
character is taken to be the terminal's ssttoopp charac-
ter.
ssuusspp If tteellnneett is in llooccaallcchhaarrss mode, or LINEMODE is en-
abled, and the ssuussppeenndd character is typed, a TELNET
SUSP sequence (see sseenndd ssuusspp above) is sent to the re-
mote host. The initial value for the suspend charac-
ter is taken to be the terminal's ssuussppeenndd character.
ttrraacceeffiillee
Thi is the file to which the output, caused by nneettddaattaa
or ooppttiioonn tracing being TRUE, will be written. If it
is set to ``--'', then tracing information will be
written to standard output (the default).
wwoorrddeerraassee
If tteellnneett is operating in LINEMODE or ``old line by
line`` mode, then this character is taken to be the
terminal's wwoorrddeerraassee character. The initial value for
the worderase character is taken to be the terminal's
wwoorrddeerraassee character.
?? Displays the legal sseett (uunnsseett) commands.
ssllcc _s_t_a_t_e The ssllcc command (Set Local Characters) is used to set or
change the state of the the special characters when the TELNET
LINEMODE option has been enabled. Special characters are
characters that get mapped to TELNET commands sequences (like
iipp or qquuiitt) or line editing characters (like eerraassee and kkiillll).
By default, the local special characters are exported.
eexxppoorrtt Switch to the local defaults for the special char-
acters. The local default characters are those of
the local terminal at the time when tteellnneett was
started.
iimmppoorrtt Switch to the remote defaults for the special
characters. The remote default characters are
those of the remote system at the time when the
TELNET connection was established.
cchheecckk Verify the current settings for the current spe-
cial characters. The remote side is requested to
send all the current special character settings,
and if there are any discrepencies with the local
side, the local side will switch to the remote
value.
?? Prints out help information for the ssllcc command.
eennvviirroonn _a_r_g_u_m_e_n_t_s_._._.
The eennvviirroonn command is used to manipulate the the variables
that my be sent through the TELNET ENVIRON option. The ini-
tial set of variables is taken from the users environment,
with only the DISPLAY and PRINTER variables being exported by
default. The USER variable is also exported if the --aa or --ll
options are used.
Valid arguments for the eennvviirroonn command are:
ddeeffiinnee _v_a_r_i_a_b_l_e _v_a_l_u_e
Define the variable _v_a_r_i_a_b_l_e to have a value of
_v_a_l_u_e_. Any variables defined by this command are
automatically exported. The _v_a_l_u_e may be enclosed
in single or double quotes so that tabs and spaces
may be included.
uunnddeeffiinnee _v_a_r_i_a_b_l_e
Remove _v_a_r_i_a_b_l_e from the list of environment vari-
ables.
eexxppoorrtt _v_a_r_i_a_b_l_e
Mark the variable _v_a_r_i_a_b_l_e to be exported to the
remote side.
uunneexxppoorrtt _v_a_r_i_a_b_l_e
Mark the variable _v_a_r_i_a_b_l_e to not be exported un-
less explicitly asked for by the remote side.
lliisstt List the current set of environment variables.
Those marked with a ** will be sent automatically,
other variables will only be sent if explicitly
requested.
?? Prints out help information for the eennvviirroonn com-
mand.
ttooggggllee _a_r_g_u_m_e_n_t_s _._._.
Toggle (between TRUE and FALSE) various flags that control how
tteellnneett responds to events. These flags may be set explicitly
to TRUE or FALSE using the sseett and uunnsseett commands listed
above. More than one argument may be specified. The state of
these flags may be interrogated with the ddiissppllaayy command.
Valid arguments are:
aauuttoofflluusshh If aauuttoofflluusshh and llooccaallcchhaarrss are both TRUE, then
when the aaoo, or qquuiitt characters are recognized
(and transformed into TELNET sequences; see sseett
above for details), tteellnneett 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 se-
quences. The initial value for this toggle is
TRUE if the terminal user had not done an "stty
noflsh", otherwise FALSE (see stty(1)).
aauuttoossyynncchh If aauuttoossyynncchh and llooccaallcchhaarrss are both TRUE, then
when either the iinnttrr or qquuiitt characters is typed
(see sseett above for descriptions of the iinnttrr and
qquuiitt characters), the resulting TELNET sequence
sent is followed by the TELNET SYNCH sequence.
This procedure sshhoouulldd 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.
bbiinnaarryy Enable or disable the TELNET BINARY option on
both input and output.
iinnbbiinnaarryy Enable or disable the TELNET BINARY option on
input.
oouuttbbiinnaarryy Enable or disable the TELNET BINARY option on
output.
ccrrllff If this is TRUE, then carriage returns will be
sent as <CR><LF>. If this is FALSE, then car-
riage returns will be send as <CR><NUL>. The
initial value for this toggle is FALSE.
ccrrmmoodd Toggle carriage return mode. When this mode is
enabled, most carriage return characters re-
ceived 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 nev-
er line feed. The initial value for this toggle
is FALSE.
ddeebbuugg Toggles socket level debugging (useful only to
the ssuuppeerr uusseerr). The initial value for this tog-
gle is FALSE.
llooccaallcchhaarrss If this is TRUE, then the fflluusshh, iinntteerrrruupptt,
qquuiitt, eerraassee, and kkiillll characters (see sseett above)
are recognized locally, and transformed into
(hopefully) appropriate TELNET control sequences
(respectively aaoo, iipp, bbrrkk, eecc, and eell; see sseenndd
above). The initial value for this toggle is
TRUE in ``old line by line'' mode, and FALSE in
``character at a time'' mode. When the LINEMODE
option is enabled, the value of llooccaallcchhaarrss is
ignored, and assumed to always be TRUE. If
LINEMODE has ever been enabled, then qquuiitt is
sent as aabboorrtt, and eeooff aanndd are sent as eeooff aanndd
ssuusspp, see sseenndd above).
nneettddaattaa Toggles the display of all network data (in hex-
adecimal format). The initial value for this
toggle is FALSE.
ooppttiioonnss Toggles the display of some internal tteellnneett pro-
tocol processing (having to do with TELNET op-
tions). The initial value for this toggle is
FALSE.
pprreettttyydduummpp When the nneettddaattaa toggle is enabled, if
pprreettttyydduummpp is enabled the output from the
nneettddaattaa command will be formated in a more user
readable format. Spaces are put between each
character in the output, and the begining of any
TELNET escape sequence is preceeded by a '*' to
aid in locating them.
?? Displays the legal ttooggggllee commands.
zz Suspend tteellnneett. This command only works when the user is using
the csh(1).
!! [_c_o_m_m_a_n_d]
Execute a single command in a subshell on the local system.
If ccoommmmaanndd is ommitted, then an interactive subshell is in-
voked.
ssttaattuuss Show the current status of tteellnneett. This includes the peer one
is connected to, as well as the current mode.
?? [_c_o_m_m_a_n_d]
Get help. With no arguments, tteellnneett prints a help summary.
If a command is specified, tteellnneett will print the help informa-
tion for just that command.
EENNVVIIRROONNMMEENNTT
TTeellnneett uses at least the HOME, SHELL, DISPLAY, and TERM environent vari-
ables. Other envirnoment variables may be propogated to the other side
via the TELNET ENVIRON option.
FFIILLEESS
~/.telnetrc user customized telnet startup values
HHIISSTTOORRYY
The TTeellnneett command appeared in 4.2BSD.
NNOOTTEESS
On some remote systems, echo has to be turned off manually when in ``old
line by line'' mode.
In ``old line by line'' mode or LINEMODE the terminal's eeooff character is
only recognized (and sent to the remote system) when it is the first
character on a line.
4.2 Berkeley Distribution June 6, 1993 8