Telnet Environment Option
RFC 1572

Document Type RFC - Proposed Standard (January 1994; No errata)
Last updated 2013-03-02
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Network Working Group                               S. Alexander, Editor
Request for Comments: 1572                      Lachman Technology, Inc.
Category: Standards Track                                   January 1994

                       Telnet Environment Option

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document specifies a mechanism for passing environment
   information between a telnet client and server.  Use of this
   mechanism enables a telnet user to propagate configuration
   information to a remote host when connecting.

   This document corrects some errors in [1].

1.  Command Names and Codes

      NEW-ENVIRON     39
          IS               0
          SEND             1
          INFO             2

          VAR              0
          VALUE            1
          ESC              2
          USERVAR          3

2.  Command Meanings

   IAC WILL NEW-ENVIRON

      The sender of this command is willing to send environment
      variables.

   IAC WONT NEW-ENVIRON

      The sender of this command refuses to send environment variables.

Telnet Working Group                                            [Page 1]
RFC 1572               Telnet Environment Option            January 1994

   IAC DO NEW-ENVIRON

      The sender of this command is willing to receive environment
      variables.

   IAC DONT NEW-ENVIRON

      The sender of this command refuses to accept environment
      variables.

   IAC SB NEW-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 NEW-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 NEW-ENVIRON IS type ... [ VALUE ... ] [ type ... [ VALUE ... ]
   [ ... ] ] IAC SE

      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 NEW-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                                            [Page 2]
RFC 1572               Telnet Environment Option            January 1994

   IAC SB NEW-ENVIRON INFO type ... [ VALUE ... ] [ type ... [ VALUE ...
   ] [ ... ] ] IAC SE

      The sender of this command is sending information about
      environment variables that have changed.  It is identical to the
      IS command, except that the command is INFO instead of IS.  Only
      the side that is WILL NEW-ENVIRON may send an INFO command.  The
      INFO command is not to be used to send initial information; the
      SEND/IS sequence is to be used for that.  The INFO command is to
      be used to propagate changes in environment variables, and may be
      spontaneously generated.

3.  Default Specification

   The default specification for this option is

      WONT NEW-ENVIRON
      DONT NEW-ENVIRON

   meaning there will not be any exchange of environment information.

4.  Motivation

   Many operating systems have startup information and environment
   variables that contain information that should be propagated to
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