Unix 系统中，telnet远程登录的environ选项有什么作用？

environ arguments...
The environ command is used to propagate environment variables across the telnet link using the TELNET
ENVIRON protocol option. All variables exported from the shell are defined, but only the DISPLAY and
PRINTER variables are marked to be sent by default. The USER variable is marked to be sent if the -a
or -l command-line options were used.

Valid arguments for the environ command are:

define variable value
Define the variable variable to have a value of value. Any variables defined by this com-
mand are automatically marked for propagation (``exported''). The value may be enclosed in
single or double quotes so that tabs and spaces may be included.

undefine variable