a.

a*
This gives you every filename that starts with a, regardless of
how many letters it has.

More on Files

In section 5.2 on page [*], we covered moving and renaming files with mv,
copying them with cp, removing them with rm, removing directories with
rmdir, and creating directories with mkdir. This chapter will cover some
more aspects of working with files.

Permissions

GNU and Unix systems are set up to allow many people to use the same
computer, while keeping certain files private or keeping certain people
from modifying certain files. You can verify this for yourself. Log in as
yourself, i.e. NOT as root.

whoami
This verifies that you are not root. Then enter the following command:

rm /etc/resolv.conf
You should be told Permission denied. /etc/resolv.conf is an essential
system configuration file; you aren't allowed to change or remove it
unless you're root. This keeps you from accidentally messing up the
system, and if the computer is a public one (such as at an office or
school), it keeps users from messing up the system on purpose.