this is the pathname of your "home" directory when you login and to which cd changes when invoked with no argument.
defines the directories searched when the shell is looking for the file to execute when processing a command.
if set to the name of a mail file the shell will inform you of the arrival of new mail.
contains the shell prompt string.
is the continuation prompt when a command spans more than one line.
The set of characters used for blank interpretation in the shell. Normally space, TAB and newline.