TELNET(1C)	    UNIX Programmer's Manual	       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 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
     "^]").  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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TELNET(1C)	    UNIX Programmer's Manual	       TELNET(1C)


	  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 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... ]
	  Displays 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.

     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 (ini-
	       tially "^]").

	  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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TELNET(1C)	    UNIX Programmer's Manual	       TELNET(1C)


	       remote system is a 4.2 BSD system -- if it doesn't
	       work, a lower case "r" may be echoed on the termi-
	       nal).

	  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 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.


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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 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(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
	       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.

	  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 proto-
	       col processing (having to do with TELNET options).
	       The initial value for this toggle is FALSE.

	  netdata
	       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 .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.


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