Linux – Where is the $HOME environment variable set

You can always put them in .profile, so they should apply for any login.

Problems occur however, if a .bash_login exists: In that case, bash won't read .profile.

If you want your variables from .profile to apply both in bash and for other logins, don't use .bash_login! Put bash specific variables in .bashrc instead.

Or alternatively, include .profile from .bash_login

$HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.

bash$ echo $HOSTNAME
foobar
bash$ sh -c 'echo $HOSTNAME'

bash$ export HOSTNAME
bash$ sh -c 'echo $HOSTNAME'
foobar

You could add the export command to one of your startup files, such as ~/.bashrc.

In Ruby (irb shown):

>> require 'socket'
=> true
>> Socket.gethostname
=> "bazinga"