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So,What is the difference between Unix and Linux?Unix is a complete operating system.There are distributors of it like BSD,Solaris
etc
Linux is basically a kernel.OS can be developed using this linux kernel.These allcome under Unix-like systems.we have different distributors likeubuntu,redhat etc
UNIX Introduction:1.Whats so special about UNIX?:supports Multiuser &Multitasking
2.Programs are designed to work together(they are like general tools).3.UNIX systems are usually split, or bundled, into various component
packages. Typical bundling includes the following:
Basic System:Basic commands and utilities.
Programming:Compilers, debuggers, and libraries.
Text Processing:Troff, macros, and related tools.
Networking:Utilities for connecting to remote machines, includingcommands like rlogin, rcp, etc.
Windowing:Graphical user interfaces such as OPEN LOOK and Motif.
4.Anyone Can Program the Unix Shell.
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Salient features of UNIX
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UNIX shellsSeveral different shells are available: you are free to choose the one that best
suits your interests or your application. The most common ones are:
sh
The Bourne shell It is a bit primitive and lacks job controlfeatures (the ability
to move jobs from the foreground to the background). Most UNIX users
consider the Bourne shell superior for shell programming or writing
command files.csh
The C shell It has a lot of nice features that aren't available in the Bourne shell,
including job control and history (the ability to repeat commands that you
have already given). There are a lot of hidden bugs.
ksh
The Korn shell is compatible with the Bourne shell, but has most of the C
shell's features plus some completely new features, like history editing (
the ability to recall old commands and edit them before executing them.) It
is also more reliable than csh
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bash
The "Bourne-again" shell developed by the Free Software Foundation. bash is
fairlysimilar to the Korn shell. It has many of the C shell's features, plus
history editing and a built-in help command.
OVERVIEW OF COMMANDS
Some commands that you type are internal, built into the shell. For example,
the cd command is builtin.That is, the shell interprets that command and
changes your current directory for you. The ls command, on the other hand,
is an external program stored in the file /bin/ls.The shell doesn't start a separate process to run internal commands. External
commands require the shell tofork and exec a new subprocess ; this takes
some time, especially on a busy system.
When you type the name of a command, the shell first checks to see if it is a
built-in command and, if so,executes it. If the command name is anabsolute pathname beginning with/, like /bin/ls, there is no problem: the
command is likewise executed. If the command is neither built-in, nor
specified with an absolute pathname, the shell looks in its search path for
an executable program or script with the given name.
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The search path is exactly what its name implies: a list of directories that the
shell should look through for a command whose name matches what is
typed.The search path isn't built into the shell; it's something you specify in
your shell setup files. The search path is stored in an environment variable
called PATH . A typical PATH setting might look something like this:PATH=/bin:/usr/bin:/usr/bin/X11:/usr/ucb:/home/tim/bin:
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