More often than not, we create variables with the intent they will hold a value. We typically then choose to act upon that value. We now know there are two distinct conditions that we need to potentially test for before attempting an operation on a variable.
In this example, we are going to use Get-CimInstance to return information about a specified Windows service. In this particular case, we are checking whether or not the variable holds an object. In the first command, we get WinRM , a valid service. I know by looking at services. This works, but you have to always remember to code for two comparisons, and it is twice as much work as a single comparison.
Luckily, there is a. Active 3 years, 4 months ago. Viewed 10k times. How can I fix this? Improve this question. DForck42 You're using references wrong.
Add a comment. Active Oldest Votes. But for the most part you probably don't need additional validation at all.
Improve this answer. Leo Leo 66 3 3 bronze badges. Great answer! The detailed information about using [ref] is really helpful. Add the param block to your function and make it mandatory. Specify a parameter of type 'System. Object' and try again. This is a required field.
Sign up or log in Sign up using Google. Sign up using Facebook. You may already have some strongly typed variables in your functions and not even realize it. Value instead. You can also use the ContainsKey method to check for the property. I am a defensive scripter. But if I can test for an error condition or an empty set of results, I can allow my exception handling be for true exceptions. I already covered those scenarios earlier in this post. It's important to know that different functions and commands handle the no results scenario differently.
But others throw exceptions or give you a status object. It's still up to you to know how the commands you use deal with the no results and error scenarios. One habit that I have picked up is initializing all my variables before I use them. You are required to do this in other languages. At the top of my function or as I enter a foreach loop, I define all the values that I'm using. Here is a scenario that I want you to take a close look at.
It's an example of a bug I had to chase down before. If there is an error, we log it. Then we check to make sure we got a valid result before processing it.
Update-Something to execute multiple times on the same object in this example. This also helps mitigate scoping issues. But because PowerShell allows variable values from outside the function to bleed into the scope of the current function, initializing them inside your function mitigates bugs that can be introduced that way. The parent scope could be another function that calls your function and uses the same variable names.
If I take that same Do-something example and remove the loop, I would end up with something that looks like this example:. Initializing the value inside your function mitigates this issue.
Naming variables is hard and it's common for an author to use the same variable names in multiple functions. So it would be very easy for values from different scopes to show up in places where they should not be. There are times when you have commands that output information or objects that you want to suppress.
I don't like the way it looks in my code but it often performs faster than Out-Null.
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