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"?