The $MAIL variable specifies which mailbox you want Bash to poll for new mail. You generally want to set this to your inbox. I use procmail, so I have many mail folders. My inbox (where mail that's actually addressed to me gets sent) is /home/blackmad/Mail/inbox, so when I get new e-mail there, Bash tells me: “You have mail in /home/blackmad/Mail/inbox.”
The PATH variable determines where, and in what order, Bash will look for executables. Each directory is separated by a colon (:). Bash interprets your path from right to left. Let's say your PATH is set to /usr/bin:/bin/:/sbin/:/sbin/. When you enter a command, Bash will look for it in its internal shell functions first, then /usr/bin, then /bin and so on, until it either finds the command or gets to the end of your PATH. Often you may simply want to append or prefix your current PATH; you can do this by specifying
PATH="/prev/path:$PATH:/next/path" export PATHIn the first example, Bash will look through /next/path and /next_next/path after it finishes with your current PATH. In the second example, Bash will first look in /prev/path. You may want to prefix your PATH with /usr/local/bin, since that is where hand-compiled programs are usually located, and these are generally more recent then those that came with your distribution. You may also want to prefix ~/bin and have a bin directory in your home directory where you can put customized versions of programs and scripts (useful if you don't have root on the box).
Since Bash just runs through your .bashrc file and executes everything in it, you can toss in programs you want to run each time you log in. At the end of my .bashrc file, I have the following:
fortune mesg y users
So whenever I log in, fortune greets me with a bit of wisdom, messages are turned on, and I find out who's logged in to the systems.
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