0 Comments
 

In the first part of the series we covered the development environment setup on how to get started with PowerShell. Now lets dive into some code. PowerShell can be used as a dynamic language. For a C# developer this can be one of the most frustrating points. In this post we will look at the following points:

  • Variables
  • If/else
  • Loops and Piping
  • Methods
  • File handling

So let’s get going Smile

Variables

When we look at a simple program of C# it might look something like this.

using System;
namespace ConsoleApplication
{
public class Program
{
public static void Main(string[] args)
{
string name = "Harvey Specter";
int number = 42;
Console.WriteLine($"Hello{name}, your number is{number}");
}
}
}
view raw Program.cs hosted with ❤ by GitHub

Now in comparison here is the equivalent PowerShell code.

Note that we do not need any Class or Method to get started. Simply start writing your script. Now variables are interesting under PowerShell. Lets add some more info to our PowerShell code to retrieve the type of the variables. The variable is assigned a type when a value is assigned. Since PowerShell is not compiled there are some potential pot holes a typical C# developer might into. For starters this is a totally valid statement.

Resulting in the following output:

Variable is first of Type Int32 after assignment of a string has the type String.

We can be more strict in PowerShell by defining the type of the variable which will make the second assignment illegal. But this requires some additional effort on your end.

If we would run the strict assignment we would be greeted by an error message which is more of what a C# developer would be used to.

And one more thing. Even though the variable $neverDefined never got defined. Well we can still access it’s value without an exception or error being raised.

PowerShell output showing that the variable $neverDefined simply shows an empty string

Keep this in mind while developing since they might just come around and bight you in the foot later on.

Conditional Operators

When writing conditional code in C#, the standard choice is using if and else or for multiple options a switch/case. So a possible option would be to use them as follows:

Apologizing to all the readers who have to work shifts Winking smile Lets look at how the same code would be implement in PowerShell:

No huge changes or surprises So no surprises here. The major difference is the equality sign in the if check. Here is a small translation table of the equality signs you find in C# and PowerShell:

Purpose

C#

PowerShell

Equal

==

-eq

Not Equal

!=

-ne

Greater Then

>

-gt

Less Then

<

-lt

Greater or Equal

>=

-ge

Less or Eual

<=

-le

Loops and Piping

There are many different constructs for looping in C#: for, while, do while and ForEach. So if we look at all the different types of loops in C#:

In PowerShell the equivalent can be  implemented like so:

Now the ForEach loop is really great when having to iterate over a list of items. This is often what we end up doing e.g. “Iterating over a list of people to get the count by city” or a bit more PowerShelly “Iterate over number of host information to ensure that everything is okay and no action is needed”. While we could write that with the above for loop, there is a PowerShell called piping. Piping allows us to Take a collection and forward it to the next operation. We could rewrite the ForEach sample as follows:

Pretty cool no? Smile We can even use the ForEach construct to loop over every item being forwarded:

Note that $_ is always the current item we are going over in the ForEach Loop. The equal construct in C# is achieved with Extension Methods. Piping can be great to enhance readability since one can see the flow. But it also can make the code harder to debug, so be sure to keep the balance here.

Note: Even though foreach is an alias for ForEach-Object they behave differently. When using foreach the operation is paused until all elements are to be processed are present, in case of ForEach-Object it will process the items as they come in. This may lead to some unexpected side effects…

Summary

In this Blogpost we saw the basic programming structures in PowerShell compared to how they would be implemented in C#. Keep in mind that PowerShell is more dynamic and forgiving at runtime than C# which might lead to some unwanted side effects. In the next Post we will look at how we can implement Methods and work with Parameters which are not only handy for methods but also for Command Line Interface parameters.

References

There is more in this blog post series:

0 Comments
 

Screenshot of a Windows Powershell from WikiPedia

Lately I have been doing some work with PowerShell. PowerShell is a well known in the Windows IT Pro space when it comes to the automation of tasks. In todays fast paced world the idea of automating mundane tasks is an attractive idea. PowerShell brings forward the basic toolset to automate, not just mundane tasks, but set up entire environments. Since I do most of my day work in C# I wanted to share some of my insights into developing with PowerShell. Which should just be enough to get into trouble Winking smile

 

The development environments

PowerShell comes right out of the box on Windows 7 or higher machines and even comes with it’s own editor the PowerShell Integrated Scripting Environment (PowerShell ISE). PowerShell ISE allows you to edit PowerShell files which includes code highlighting and IntelliSense and run them in Debug mode (F5) or running the selected code parts (F8). It is even possible to set breakpoints (F9) which should make C# developers feel right at home.

image

An interactive PowerShell displays the output of the running script. The shell also comes in handy while debugging your code. At a given breakpoint you can inspect the variable by typing it's name into the console. There only rant I have about the PowerShell ISE is that the console not be reset. The only way this can be achieved is by restarting the editor and having to open (all) the files again.

Visual Studio

As a C# developer the daily driver usually is Visual Studio. If you can’t bear the thought of using a different Editor. Well you are covered. The experience is much like with the PowerShell ISE. So if you have any Visual Studio Plugins such as VsVim you do not want to miss this may be your preferred route.

 

If you haven’t installed PowerShell during the initial installation of Visual Studio. You can add PowerShell by modifying your Visual Studio installation. Open Programs and Features, choose Visual Studio and then select Change. In the dialog select Modify and choose PowerShell Tools for Visual Studio. Finally select Next.You might want to get a cup of your favourite beverage while the installation is taking place.

Visual Studio will create it’s usual Solution and Project files. This will result in some extra clutter that your average PowerShell developer might not recognise. Keep this in mind when you check those files into your repo.

Beyond Windows

PowerShell is usually run on top of the .Net Framework. As of lately PowerShell also supports running on .Net Core. This means your PowerShell scripts are not limited to Windows. You can write them also for Apple and Linux machines. One of the PowerShell editors of choice for Linux and Mac, would be Visual Studio Code and the PowerShell Plugin for it.

image

You can see an extensive description on how to use PowerShell with Visual Studio Code on the msdn website.

Why choose PowerShell over C# or CScript

reactions why ryan reynolds but why

Since PowerShell runs on the .Net Framework, why should we use PowerShell in the first place? Wouldn't it be easier to just write the code with C# in the first place? One of the best arguments in my opinion comes from the reason why PowerShell came to be. It is designed from it's roots up to automate IT tasks. There are many hooks in the OS or other major Services. Active Directory, IIS, Exchange and many more provide interfaces that can be consumed with PowerShell. So if your task is to automate a Windows environment, PowerShell will be able to consume and interact with many existing APIs. Making the task easier and less time consuming.

A fun fact is that the UI for configuring IIS actually performs PowerShell commands in the background. The identical commands are used when invoking them through a PowerShell script.

Since we are writing infrastructure code there is a good chance that an Ops person will end up maintaining it. There is a good chance that this person has an interest in putting in the effort of learning PowerShell. Since it is their day job and PowerShell is sought out to enable them during their daily tasks.

And third, it is always fun to dive into a new programming language. And finally PowerShell has a way to interact with C#. So if the need ever arises to get stuff done the good old C# way there is nothing stopping you Smile

Hello PowerShell

Before we end this post, let’s see the Hello World Example:

echo "Hello PowerShell"

Jup that is it, one line and we are done.

In the next post we will dive into the basics of writing PowerShell code.

References

There is more in this blog post series: