When IDL starts, it sets the values of a variety of system
variables. System variables are a special class of predefined
variables that are available to all IDL program units; they are
described in detail in System Variables. The values of some
system variables can be specified by the user when IDL starts,
either via operating system environment variables or via
preferences specified within the IDL Development Environment. In
order to set these system variables, IDL does the following
things when it starts up: The process used to set environment
variables varies depending on the operating system you are
using. On UNIX systems, environment variables are generally
specified in a file read by your shell program at startup.
Syntax for setting environment variables varies depending on the
shell you are using, as does the file you use to specify the
variables. If you are unsure how to set environment variables on
your system, consult the system documentation or a system
administrator. For example, to set the enviro