Microsoft® PowerShell, VBScript and JScript® Bible

Chapter 4. PowerShell Fundamentals

IN THIS CHAPTER

• Introducing the structure of PowerShell, and how it can be extended

• Understanding the different kinds of PowerShell commands

• Using PowerShell variables

• Working with Objects in PowerShell

• Using Loops and control flow in PowerShell

Let's start by getting the obvious thing about PowerShell out of the way. It is a shell. The UNIX world has had a number of shells (the C shell, Korn shell, BASH, and so on), but the Microsoft world has a single shell, COMMAND.COM in the DOS-based operating systems, and its successor CMD.EXE in the NT-based ones. The term "shell" refers to a piece of software that wraps around the operating system kernel. The shell is an environment where commands can be entered to run other programs and text output from those programs can be displayed. Some basic tasks might be built into the shell itself—such as getting a listing of files in the current directory, copying and deleting files, and so on. With the Microsoft shells, it is sometimes difficult to know which commands are built into the shell (such as copy) and which are separate utility programs (such as Xcopy).

Shell Fundamentals

Most shells include some kind of scripting language; at their simplest, these are simply lists of commands that could have been typed in the interactive shell, but are executed as a batch task. The Microsoft shells have had batch files from the early days of DOS and although each new release has added some features, the language has remained ...