Background

Before I get into the details of Unix shell scripting I must first discuss the background needed to understand the task.

An Operating System

An Operating System (OS) is a set of programs and routines which control the underlying hardware (h/w) that makes up the computer. This in turn allows the user to control many aspects of the computer in terms of running programs or applications - also known as software (s/w).

A shell is typically supplied with an OS and acts like a command line interpreter of OS commands. A shell script is a sequence of OS commands that gets runs under the shell. Because the type of shell you run depends on the type of OS you run, I think it is pertinent to discuss the various types of operating systems available today.

There are many different types of operating systems available (Google Chrome is new) depending on the manufacturer of the hardware that supplies the OS. In today's era there are three major types of operating systems used in the market.

The Mac operating system - created by vendor Apple, Inc. is known as OS X which has been around since 1999. The following summarizes the variations of OS X over the past several years.

1999 - 1.0 - Hera

2000 - Beta - Kodiak

2001 - 10.0 - Cheetah

2001 - 10.1 - Puma

2002 - 10.2 - Jaguar

2003 - 10.3 - Panther

2005 - 10.4 - Tiger

2007 - 10.5 - Leopard

2009 - 10.6 - Snow Leopard

The PC operating system - created by vendor Microsoft, Inc. is known as DOS/Windows which has been around since 1981. The following summarizes the variations of Windows over the past several years.

1981 - 1.0 - Shell that ran under Windows called DOS Executive

1987 - 2.0 - Windows

1990 - 3.0 - Windows

1992 - 3.1 - Windows (3.11 known as workgroup, first time DOS is bypassed)

1993 - 3.1 - Windows NT (New Technology)

1995 - 4.0 - Windows 95

1998 - 4.1 - Windows 98

1999 - 4.1 - Windows 98 SE (Special Edition)

2000 - 4.9 - Windows ME (Millennium)

2000 - 5.0 - Windows 2000

2001 - 5.1 - Windows XP (Home and Professional)

2002 - 5.1 - Windows MC (Media Center)

2007 - 6.0 - Windows Vista

2009 - 7.0 - Windows 7

The Unix operating system - created by vendor AT&T @Bell Labs, Inc. is known as Unix which has been around since 1970's. Because Unix has evolved into many different flavors (depending on the vendor) we cannot list this s/w by version but instead will discuss the major contributors and introduction of Open Source and Linux.

1970's - Project Unics was developed to support 2 concurrent users (later changed to Unix)

1980's - AT&T released Unix System III, HP released HP-UX, IBM released AIX, Sun released Solaris, GNU project was developed (for free unix s/w)

1990's - BSD (Berkley Software Design) introduced BSD Unix, Linus Torvalds released the Linux kernel, The SCO Group (Santa Cruz Organization) introduced SCO Unix

2000's - Linux distributions became popular using the Linux kernel with their own flavor and creating the Open Source market.