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CHAPTER 18 INTRODUCING DARWIN AND THE SHELL
Darwin Basics
The first thing you need to know when working with Darwin is some of the common language
used, in order to avoid confusion. Second, you need to know how files are organized; and finally,
you need to know how to move around the file system.
NOTE When we talk about files here, we are not just talking about the last text file you created;
Darwin treats everything as a file. For example, a directory (a.k.a. folder) is a file that
contains other files. Each file has a number of properties that will determine how the shell
treats that specific file; if it’s an application, the shell will launch it; if it’s a directory, the shell
will know that it can access other files contained in it. We’ll cover file properties a bit later.
Darwin Semantics
To avoid confusion as the chapter proceeds, we should quickly go over some of the important
terms used in Darwin and how they compare with terms used in the Finder. Table 18-1 defines a
handful of terms used commonly in Darwin (and other UNIX systems), gives the Finder equivalent
or alternate term, and adds any relevant notes. While there are many other terms you’ll
come across, these basics will be used repeatedly, so they are good to know.
Table 18-1. Darwin Terms Explained
Finder or
Darwin Term Alternate Term Notes
File File (and others) Darwin treats all items, documents, directories,
and applications as files; in the Finder, when we
talk about a file, we are generally talking
specifically about a document.
Directory Folder Folders are generally referred to as directories.
Root directory, or / Top level of hard drive Not to be confused with the root user, the root
directory, which is represented by the / symbol, is
the highest level of the Darwin file structure.
Root (user) Administrator In addition to the root directory, there is also
a root user. The root user (also known as the
superuser) has the ability to do just about
anything in the Darwin environment, including
irreparably destroying it. To maintain a secure
system and avoid devastating problems, certain
files require root privileges to read, write, and
execute. While the administrator is the closest
thing to root in Aqua, it’s not quite the same, as
root actually has more abilities.
Link (specifically a Alias A link in Darwin functions the same way as an
symbolic link) alias does in the Finder (and appears as such
when viewed in the Finder). While the function
of a symbolic link and an alias are the same, it’s
worth knowing that they are implemented
differently.