


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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	  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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	       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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	       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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