RFC 1408 (rfc1408) - Page 2 of 7
Telnet Environment Option
Alternative Format: Original Text Document
RFC 1408 Telnet Environment Option January 1993
IAC DO ENVIRON
The sender of this command is willing to receive environment
variables.
IAC DONT ENVIRON
The sender of this command refuses to accept environment
variables.
IAC SB ENVIRON SEND [ type ... [ type ... [ ... ] ] ] IAC SE
The sender of this command requests that the remote side send its
environment variables. The "type" may be either VAR or USERVAR,
to indicate either well known or user variable names. Only the
side that is DO ENVIRON may initiate a SEND command. If a list of
variables is specified, then only those variables should be sent.
If no list is specified, then the default environment, of both
well known and user defined variables, should be sent. If one of
the variables has no name, then all the variables of that type
(well known or user defined) in the default environment should be
sent.
IAC SB ENVIRON IS type ... [ VALUE ... ] [ type ... [ VALUE ... ] [
The sender of this command is sending environment variables. This
command is sent in response to a SEND request. Only the side that
is WILL ENVIRON may send an IS command. The "type"/VALUE pairs
must be returned in the same order as the SEND request specified
them, and there must be a response for each "type ..." explicitly
requested. The "type" will be VAR or USERVAR. Multiple
environment variables may be sent. The characters following a
"type" up to the next "type" or VALUE specify the variable name.
The characters following a VALUE up to the next "type" specify the
value of the variable. If a "type" is not followed by a VALUE
(e.g., by another VAR, USERVAR, or IAC SE) then that variable is
undefined. If a VALUE is immediately followed by a "type" or IAC,
then the variable is defined, but has no value. If an IAC is
contained between the IS and the IAC SE, it must be sent as IAC
IAC. If a variable or a value contains a VAR, it must be sent as
ESC VAR.
If a variable or a value contains a USERVAR, it must be sent as
ESC USERVAR. If a variable or a value contains a VALUE, it must
be sent as ESC VALUE. If a variable or a value contains an ESC,
it must be sent as ESC ESC.
Telnet Working Group