HOSTNAME environment variable on Linux

HOSTNAME environment variable on Linux


The Question: On my Linux box (Gentoo Linux 2.6.31 to be specific) I have noticed that the
HOSTNAME environment variable is available in my shell, but not in scripts. For
example,
$ echo $HOSTNAME
returns
xxxxxxxx.com,
but
$ ruby -e 'puts ENV["HOSTNAME"]'
returns
nil
On the other hand, the USER environment variable, for instance, is available
both in the shell and in scripts.
I have noticed that USER appears in the list of environment variables that
appears when I type
export
i.e.,
declare -x USER="infogrind"
but HOSTNAME doesn't. I suspect the issue has something to do with that.
My questions: 1) how can I make HOSTNAME available in scripts, and 2) for my
better understanding, where is this variable initially set, and why is it not
"exported"?

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