WhatIs-PowerShell -?

PowerShell is Microsoft’s scripting alternative to ye olde DOS command line.  Although it shares many of it’s concepts, it it immensely more flexible and extensible.

It’s primary purpose is to allow system admins to accomplish more through a command line interface and scripts using a more standard command syntax than the collection of DOS commands, VBScripts and random executables that are available with the standard cmd.exe interface.

At it’s base it’s an interactive shell that allows you to type commands and view the results.  Like the DOS command line, you can create script files (.PS1 instead of .BAT).  Unlike the DOS command line you can load extensions in the form of Snap-ins and Modules (Snap-Ins are a version 1 concept that can still be loaded but have largely been replaced by Modules in version 2).

CmdLets & Providers

There are two important concepts in PowerShell, CmdLets and Providers.

CmdLets are commands you type at the command line such as Set-Location and Get-ChildItem.  Note that these can be aliased.  You can type Del *.txt and it will delete all text files in the current folder because Del is an alias of Remove-Item. 
You’ll notice that the non-aliased naming convention for CmdLets is Verb-Object.  Not only that, but if you define a CmdLet or function that doesn’t use one of the pre-defined verbs, PowerShell will yell at you, although it will still function correctly (You can get a list of approved verbs by typing Get-Verb).

Providers on the other hand allow you to navigate systems through a folder system.  The most obvious is the file system.  The File System provider allows you to type CD C:\Users (translates to Set-Location C:\Users) which will set your current location to the C:\Users folder.

However, unlike the DOS command line, we’re no longer limited to the file system.  Load up the SQL Server provider, type CD SQL:\MYSQLSERVER\DEFAULT\Databases\MyDatabase\Tables, type Dir (translates to Get-ChildItem) and you’ll get a list of the tables in the MyDatabase database on the default SQL instance on MYSSQLSERVER.   there are also providers for the registry and IIS, allowing for easy navigation.