I just spent a month updating one of our PowerShell modules to support Linux and MacOS. I learned a lot that I wanted to share with the community as cross-platform support becomes more and more important.
Use “Environment” Class Properties Instead of “env:” Drive
Environment variables are different between the different operating systems. All of them have
PATH , but not much else. Windows and MacOS both have variables for the temp directory, but they have different names.
And we’re back! Ok, so in the last blog we began a conversation about delegates and using LINQ in PowerShell. In today’s post, I’m going to give an example of how it can be incredibly useful. Let’s talk about Joins.
Joins
In my line of work, I’m constantly running into the need to combine datasets from multiple sources that relate to each other and pull out some specific properties. Say you have two internal services, one which is used to track production status and another which is used to monitor whether machines are online. To demonstrate this, let’s initialize some mock data once again.
Greetings PowerShellers! Lately, I’ve been itching to write something up on Microsoft’s Language-Integrated Query (LINQ). You’ve likely encountered it if you’ve done any development in C#. LINQ is an incredibly powerful querying tool for performing look-ups, joins, ordering, and other common tasks on large data sets. We have a few similar cmdlets built into PowerShell, but other than the ‘.Where()’ method on collection objects nothing that comes close to the speed at which LINQ operates. To dig into this topic, we’re going to have to do a quick high level overview of a couple of other .NET staples often encountered in the C# world. You see, unlike most .NET methods which accept object types like integers, strings, and the like, LINQ uses static extension methods which only accept delegate object types. What are delegates? In application development, there is an occasional need for objects within memory to communicate with each other for things such as “button click events.” To address this, the Windows API uses function pointers to create callback functions which then report back to other functions in your applications. Within the .Net Framework, these are called delegates. Delegates are objects that point to another method, or possibly many methods, by storing three key pieces of information: the address of the method on which it makes calls, the parameters (if any) of this method, and the return type (if any) of this method. With this information, a delegate object is able to invoke these methods dynamically at runtime, either synchronously or asynchronously. With this information, a delegate object is able to invoke these methods dynamically at runtime, either synchronously or asynchronously. A simple example of this in C# looks like this:
PowerShell provides a tremendous boon to productivity for computer professionals of all types. But, you have to admit: it can be a bit daunting to get up to speed! Indeed, as someone who has a fair amount of experience using it, I still find myself having to look up how to do things–frequently. So I started keeping track of the recipes I was using the most. And came up with a list of 400 or so, published in 4 parts.
You can certainly find a number of articles around that present PowerShell pitfalls that can easily trip you up if you are not careful. I took a different approach in my three-part series, A Plethora of PowerShell Pitfalls. The first two parts are presented in quiz format, together covering the top 10 “gotchas”. They will help you test your awareness to see if you even realized the danger and did not know you’ve been skirting those traps for awhile. After you’ve had an opportunity to consider the conundrums presented, I then go into detailed explanations for why they happen and how to fix them. The third and final part is a compendium of all the common “gotchas” that I put together after reviewing all the other lists out there. The more than 35 entries in the list cover, I believe, a good 98% of the issues you would likely encounter. Yes, there are more esoteric pitfalls as well, but I ran out of web page… 🙂 Part 1: Pesky Parameter Problems Part 2: A Portion of Potential Puzzles Part 3: The Compendium
Pipelining is an important concept in PowerShell. Though the idea did not originate with PowerShell (you can find it used decades earlier in Unix, for example), PowerShell does provide the unique advantage of being able to pipeline not just text, but first-class .NET objects. Pipelining has several advantages:
It helps to conserve memory resources. Say you want to modify text in a huge file. Without a pipeline you might read the huge file into memory, modify the appropriate lines, and write the file back out to disk. If it is large enough you might not even have enough memory to read the whole thing.
It can substantially improve actual performance. Commands in a pipeline are run concurrently-even if you have only a single processor, because when one process blocks, for example, while reading a large chunk of your file, then another process in the pipeline can do a unit of work in the meantime.
It can have a significant effect on your end-user experience, enhancing the perceived performance dramatically. If your end-user executes a sequence of commands that takes 60 seconds, then until 60 seconds has elapsed he/she would see nothing without pipelining, whereas output could start appearing almost immediately with pipelining.
PowerShell provides a variety of techniques for using pipelining but it is all to easy to do it wrong, so you think you are pipelining but in fact you are not. In my article Ins and Outs of the PowerShell Pipeline, I discuss the most common things that can trip you up with implementing pipelining and how to avoid them.
Regular Expressions is often referred to as wizardry or magic and for that reason I stayed away from it for most of my career. I used it only when I had to and most of the time just reused examples that I found online. There’s nothing wrong with that of course, but I never took the time to learn it. I thought it was reserved for the elite. Turns out that it’s not that complicated and that I had been using it for years without knowing it. In an effort to shorten the learning curve for others and to show you the value of learning regular expression I’ve written a blog post titled A Practical Guide for Using Regex in PowerShell. It will walk you through how to use regular expression in PowerShell and gives you a glimpse into how powerful regular expression is. Below is an example of how to use regular expression to extract a user’s name from their distinguished name in Active Directory. To learn more check out this blog post. Topics Covered
Do you spend hours a day in PowerShell? Switching back and forth between PowerShell windows getting you down? Have you ever wanted “Quake” mode for your terminal? If we are going to spend so much time in PowerShell, we may as well make it pretty. Check out the Ultimate PowerShell Prompt Customization and Git Setup Guide for how to:
Sometimes, as a developer, you want to be be able to keep track of free space on a drive, the size of a log, the load on your CPU, the number of users logged in, etc. With PowerShell, it is typically just a matter of finding the right cmdlet amidst the large (and rapidly growing) pool of cmdlets provided by Microsoft and by third parties. Then you just run Get-Foo to check details about the foo resource. And then you come back 5 minutes later and run it again because you want to see how it changes over time. But wouldn’t it be nice if you could just have it run automatically at regular intervals in a separate window that you could just keep in the corner of your screen? Well, I found the barebones of just such a utility sometime ago (authored by Marc van Orsouw, aka ‘thePowerShellGuy’). His original post is no longer available, but I expanded upon his code and, over time, added features, bug fixes, and enhancements, making it more useful and more user-friendly. Here are a few screenshots of the Monitor Factory in action. Monitor the size of a database
At the beginning of July, we welcomed our 3rd son into the world. As days past my wife and I would say, “wow, he’s 11 days old. Can you believe it?!”. I’m sure parents out there are relating to this! This gave me an idea for a fun script that would get your age in years, months and days, tell you how many days until your birthday and your star sign. I wanted date of birth passed to the function as ‘dd/MM/yy’. To keep to this format, I’m using the ‘ValidatePattern’ Advanced Parameter with a Regular Expression (Regex). The regular expression, “^(0[1-9]|[12]\d|3[01])/(0[1-9]|1[0-2])/(\d{2})$”, will only allow a date in the format of 01/01/16, for example. Briefly, here is regex syntax I used in some of the expression: ^ Start of string ( .. ) Capturing group (0[1-9] Match two digits that make up the day. This accepts numbers from 01 to 09 | Acts like a Boolean OR. /d match any digital character [12] match any character in the set / used to divide the date numbers {2} Exactly two times $ End of string Now that my function parameter variable $Bday has a date, its passed to get-date to be converted from a string to a date. The date in variable $cDate will look like this, ‘01 January 2016 00:00:00’. The next line in the code will use todays date and subtract the date passed in $cDate variable. The $diff variable will contain the following data which we will use to get our age in years, months and days: Days : 212 Hours : 12 Minutes : 40 Seconds : 20 Milliseconds : 533 Ticks : 183624205335135 TotalDays : 212.528015434184 TotalHours : 5100.67237042042 TotalMinutes : 306040.342225225 TotalSeconds : 18362420.5335135 TotalMilliseconds : 18362420533.5135 I’ve contained this first part in our Begin block. The Process block does the main code. Now I need to get my age in Years, Months and Days. This is where the [math] data type is used. I’m using the ‘Truncate’ property as I don’t want to do anything fancy like round up my numbers. Adding the .typename of Days to my $diff variable and dividing by $daysInYear variable I can get my age in years. The next two, months and days required a tweak to the algorithm. I ended up using a maths term called a ‘Mod’. Now I’m not talking about youth culture and style in the sixties (Mods and rockers anyone ??), but the Modulus Math Operator. Basically the Modulus Operator returns the remainder when the first number is divided by the second. So for example: 1 mod 3 = 1 (or 1 % 3 = 1) 2 mod 3 = 2 3 mod 3 = 0 4 mod 3 = 1 The operator sign used is % for Modulus. Not to be confused for the alias of foreach in PowerShell. For days in a month, I used the average of 30. I thought it would be fun to add the star sign as well. I was after something that could tell me, “is this date in this date range?”. One of the properties of ‘get-date’ is DayOfYear. Finding if a number is in a range is pretty straight forward, For example:
