2. Unix - Behind the Curtain

-Probably the single most important concept for would-be power users to grasp is that you don't talk to UNIX directly

-Instead, you talk to a program called the shell

-The UNIX operating system proper is referred to as the kernel

-Usually, only programs talk to the kernel (through system calls)

How it Works ???

-Users talk to the shell, which interprets their commands and either executes them directly or passes them on to other programs. These programs in turn request lower-level services from the kernel.

-First of all, you can choose between several different shells , each of which may have different rules for interpreting command lines

-Second, the shell has to interpret the command line you type and package it up for the command you are calling. Because the shell reads the command line first, it's important to understand just how the shell changes what it reads.

-One basic rule is that the shell uses "white space" (spaces or tabs) to separate each "argument" of a command

-But sometimes, you want the shell to interpret its arguments differently.The shell lets you do this by quoting arguments