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to do on a Linux system, chances are there is already a command (or a sequence
of commands) which will do it.
Finally, we will discuss the extent of our remaining ignorance upon
finishing the chapter.
Let us take a moment to explain that last comment. As readers of comput-
er topics ourselves, we are often frustrated when we discover how lightly a topic
has been covered, but particularly so when other parts of the same topic are
found to fully explore their topics. When only some parts of a topic are thor-
ough, you often don't know that you don't know it all. We will introduce some
basic shell concepts and commands here, and we may expand on some of these
in later chapters, but each of our chapters covers topics that could each fill its
own topic. Therefore we need to leave out lots of material. We will also let you
know when we have left things out because they are off-topic, or because we
don't have room. We'll also try to tell you where to look for the rest of the
knowledge. We try to sum this up in a final section of each chapter entitled
What You Still Don't Know. But we do have a lot of information to impart,
so let's get going.
1.2
T
HE
C
OMMAND
L
INE
:W
HAT
'
S THE
B
IG
D
EAL
?
One of the revolutionary things that UNIX (and thus Linux) did was to sepa-
rate operating system commands from the operating system itself. The com-
mands to display files, show the contents of directories, set permissions, and so
on were, in the “olden days,” an integral part of an operating system. UNIX
removed all that from the operating system proper, leaving only a small “kernel”
of necessary functionality in the operating system. The rest became executables
that lived outside of the operating system and could be changed, enhanced, or
even replaced individually by (advanced) users without modifying the operating
system. The most significant of these standalone pieces was the command
processor itself, called the shell.
The shell is the program that takes command-line input, decides what
program(s) you are asking to have run, and then runs those programs. Before
there were Graphical User Interfaces, the shell was
the
user interface to UNIX.
As more developers began working with UNIX, different shells were developed
to provide different features for usability. Now there are several shells to
choose from, though the most popular is
bash
. Some BSD/UNIX die hards
