Scripting with PowerShell

Scripting is always a preferred choice for IT, businesses, server administrators, DBAs and professionals who aim to automate or schedule their routine tasks with flexibility and control. It not only makes you more productive but also improves your daily tasks.

The lack of task automation makes an emerging business lose most of its time and effort on managing its administrative tasks. You may have done tons of things to advertise your business, but when it comes managing your tasks you probably need something that makes your life a lot.

Introduction

Windows PowerShell is one of the powerful command line tools available for scripting. If you are familiar with Unix, DOS or any other command based tools, you would easily get expertise over PowerShell.

Your first script

A simple script in PowerShell can be written in a notepad. it is a sequence of commands called cmdletsthat will be executed one at a time.

1. Open notepad
2. Type a string: ‘Printing current date time..’
3. Type a cmdlet in next line: get-Date
4. Save file: MyFirstScript.ps1
5. Right click on the file and click ‘Run with PowerShell’
6. You can see the current date time printed on PowerShell Console

Whatever you type in double quotes, is displayed on the console and cmdlets gets executed.

Getting PowerShell on your machine

There is no need of additional installation for the tool, it is a part of Windows 7 and above by default. For earlier versions, it can be downloaded from Microsoft Scripting Center.

Just type windows or powershell in search area after pressing windows logo and you will find two PowerShell menus

Windows PowerShell is for plain console while ISE is Integrated Scripting Environment to write, test and execute scripts in the same window.

Building Blocks

Let us quickly get acquainted with the terminology to start coding. Here are the basic terms used –

Cmdlets

Commands written in PowerShell are named cmdlets(pronounced as ‘command lets’)which are the foundation of scripting. You can write a series of cmdlets to achieve your tasks. It is written as a verb-noun pair which is easy to remember and self-explanatory.

If we execute following cmdlet, it lists down all the childs from current location –

PS C:\> Get-Childitem

(Get – verb, Childitem – Noun)

Each cmdlet has an associated help file to know about its syntax – Description and parameters required to invoke it correctly. You can use cmdlet ‘Get-Help’ for same.

Aliases

Let us observe the following commands –

The cmdlet Get-childitem returns the list of files/folders in current directory in this case – C drive.

If you look at other two commands – dir and ls, both return the same result. Does that mean there are duplicate commands to solve the same problem?

No, these both are aliases to ‘Get-childitem’. You can create handy aliases of your important commands and use it. This is the reason why your DOS and Unix commands work seamlessly with PowerShell.

Following command sets alias for Set-Location cmdlet

PS C:\> New-Alias Goto Set-Location

You can find out existing aliases by command type – ‘Alias’ on your machine

PS C:\> Get-Command –Name *

Pipeline

You can use output of one cmdlet in another using pipe character (|). As an example you want to collect some data and then copy the output to a file, you can simply do it with one-line syntax

PS C:\> Get-Childitem | Export-Csv out.csv

Redirection

Two Redirection operators used are > and >>.

These enable you to send particular output types to files and output stream

Code	Message Type
*	All output
1	Success
2	Error
3	Warning
4	Verbose
5	Debug

Following command writes the out to a file instead of console

PS C:\> Get-Childitem * > out.txt

Operators

Like any other scripting language, PowerShell also provides an exhaustive list of operators to write powerful scripts. Some of the basic operators are listed for your reference here:

Operator	Symbol	Definition
Assignment	“=,+=,-=,*=,/=,%=,++,–“	Assigns one or more values to a variable
Comparison	“-eq, -ne”	Equal, Not equal
	“-gt,-ge”	Greater than, Greater than or equal to
	“-lt,-le”	Less than, Less than or equal to
	“-replace”	Changes specified element in a value
	“-match, -notmatch”	Regular expression matching
	“-like, -notlike”	Matching wildcards
	“-contains,-notcontains”	Returns TRUE if the value on its right is contained in the array on its left
	“-in, -notin”	Returns TRUE only when given value exactly matches at least one of the reference values.
Logical	“-and, -or, -xor, -not, !”	Connect expressions and statements, allowing you to test for multiple conditions
Bitwise	“-band”	Bitwise AND
	“-bor”	Bitwise OR (inclusive)
	“-bxor”	Bitwise OR (exlcusive)
	“-bnot”	Bitwise NOT
String	“-Split”	splits a string
	“-join”	joins multiple strings

Execution Policy

Powershell executes cmdlets as per set execution policy of the machine or server. Sometimes it becomes necessary to explicitly set the policy on the scripts before executing on different machines.

The Set-ExecutionPolicy cmdlet is used for the purpose which has four options to choose from –

Policy	Definition
Restricted	No scripts can be run. PowerShell can be used only in interactive mode
AllSigned	Only scripts signed by a trusted publisher can be run
RemoteSigned	Downloaded scripts must be signed by a trusted publisher before they can be run
Unrestricted	No restrictions – all scripts can be run

Useful Commands

There are more than two hundred in-built cmdlets for use and developers can built complex ones by using the core commands. Some of the useful commands are listed below:

Cmdlet	Syntax	Output	Usage
Get-Date	Get-Date	Sunday, March 26, 2017 6:12:40 PM	Gets current date and time
(Get-Date).AddMinutes	(Get-Date).AddMinutes(60)	Sunday, March 26, 2017 7:12:40 PM	Adds 1 hour to current date and time
Copy-Item	Copy-Item c:\source.txt d:\destination	Copy source.txt to destination folder	Copying files and folders
Clear-Eventlog	Clear-Eventlog -LogName	Clears all enteries from specified event log
Restart-Service	Restart-Service -Servicename	Restarts service
Get-ChildItem	Get-ChildItem	Gets all files and folders	Some parameters make his more useful – force – to run without user confirmation on special folders include – to include certain files or folders exclude – to exclude certain files path – specified path instead of current directory
Set-Content	Set-Content C:\textFile.txt “Text being added here from PowerShell”	Saves text to a file
Remove-Item	Remove-Item C:\test -Recurse	Removes all contents from a folder	User will not be prompted before deletion
(Get-WmiObject -Class Win32_OperatingSystem -ComputerName .).Win32Shutdown(2)	(Get-WmiObject -Class Win32_OperatingSystem -ComputerName .).Win32Shutdown(2)	Restart current computer

Real-world Scenario

Let’s see how PowerShell made the life of a server administrator easy!

John Bell, one of the system administrator of an MNC is catering to some 2000 users and update patches on their desktops remotely through Windows Server 2010 and MS System Center Configuration Manager, SCCM. Now, when one or more patches get scheduled to run during night hours, often they failed on couple of machines due to disk space scarcity and lots of manual intervention and rework is required to close the current job. One of his colleagues suggested to take a proactive approach and get a list of machines with details of what is being stored on C drive, a day before patch execution job, so John decided to create a powershell script to get executed through SCCM on client machines automatically and send give a detailed report in a csv file to review the data usage and bottle necks.

Here is what he wrote (added inline comments for clarity) –

Output is a csv file –

CompName	TotalSpace	FreeSpace	Name	Size	In	% of HDD
<compName>	99.99999619	29.15378189	Program Files	2.12	GB	2.12

Conclusion

PowerShell is extremely powerful and handy when comes to manage server and database tasks and can quickly automate tasks for you. Give it a try! Happy Coding!