Shell Scripting 1 (Introduction)

The first version of UNIX was created in 1969 by Kenneth Thompson and Dennis Ritchie, system engineers at AT&T's Bell Labs., and has since grown to become the most widely used operating system.

General Characteristics of UNIX as an Operating System (OS):

Multi-user & Multi-tasking:-

most versions of UNIX are capable of allowing multiple users to log onto the system, and have each
run multiple tasks. This is standard for most modern OSs.

Over 30 Years Old :- 

UNIX is over 30 years old and it's popularity and use is still high. Over these years, many variations
have spawned off and many have died off, but most modern UNIX systems can be traced back to the original versions.
It has endured the test of time. For reference, Windows at best is half as old (Windows 1.0 was released in the mid 80s, but it was not stable or very complete until the 3.x family, which was released in the early 90s).

Large Number of Applications :–  There are an enormous amount of applications available for UNIX operating systems. They range from commercial applications such as CAD, Maya, WordPerfect, to many free applications. 

Free Applications and Even a Free Operating System:-

of all of the applications available under UNIX, many of them are free. The compilers and interpreters that we use in most of the programming courses here at UMBC can be downloaded free of charge. Most of the development that we do in programming courses is done under the Linux OS.

Less Resource Intensive :- In general, most UNIX installations tend to be much less demanding on system resources. In many cases, the old family computer that can barely run Windows is more than sufficient to run the latest version of Linux.

Internet Development :- Much of the backbone of the Internet is run by UNIX servers. Many of the more general web servers run UNIX with the Apache web server - another free application.

Unix Family (Flavors):

Linux: Red Hat Linux (RedHat Softwares)
Solaris: By Sun Microsystems
Fedora: Owned by Redhat Softwares.
IBM-AIX: IBM
HP-UX: HP
OEL Oracle enterprise Linux: Oracle
And many more.

History Of Linux:

The History of Linux began in 1991 with the commencement of a personal project by a second year student of Computer Science at the University of Helsinki , Linus Torvalds, to create a new free operating system kernel. Since then, the resulting Linux kernel has been marked by constant growth throughout its history.

Features of Linux (Why Linux?):

Free:
A Linux Distribution has thousands of dollars worth of software for no cost.

Open Source:
Free software along with the Source Code and Documentation.

Multitasking:
Capable of Running multiple application and process at same time.

Multiuser:
Allow multi users to login and user the resources at same time

Reliability:
Large Servers are running successfully without any down time (Reboot).

Difference between Microsoft Windows and Linux:

Open Source:
Windows : No access to the Source code.
Linux : Full access to the Source code

GUI (Graphical User Interface):
Windows : User Friendly
Linux : GUI but less User Friendly.

Price:
Windows : Price $50 to $150 Per each license copy.
Linux : Its Free or Much lower Price than Windows.

Reliability:
Windows : Reliable but cannot match the reliability of Linux.
Linux : Reliability (Can run for Month and Years without reboot)

Publishing:
Windows : Licensing restrictions.
Linux : Licensing Freedom.

Security:
Windows: Although Microsoft has made great improvements over the years with security on their operating system, their operating system continues to be the most vulnerable to viruses and other attacks.
Linux : Linux is and has always been a very secure operating system. Although it still can be attacked when compared to Windows, it much more secure.

File System:
Windows: Windows typically uses FAT32 or NTFS file systems.
Linux : Linux typically uses the ext2 or ext3 file systems

Directory Structure:
Windows : Flat Directory structure
Linux : Hierarchy or root Based Directory Structure