How does Powershell display variable operation work? - windows

Question

In powershell
$a = 4;
$a
will write 4 to the output stream.
Write-Ouput $a
writes 4 to output stream
Can you explain which operation is better performance wise if all I want to do is write variables to output stream?

Answer 1

If you just want to see what's in your variable, you should use a dollar sign with the name of your variable. This is most likely the fastest method to display the value of the variable.
UPDATE
Short answer: You should use just $a in order to write data in the output stream. It's the fastest way to do that.
Long answer with explanation:
If you write something like $a, then it goes directly to the output stream of the current PowerShell process, in other words, it goes to the output pipeline. This is because in PowerShell you have in general only three types of possible statements:
Definition statement: They are everything that you can define in your code for further use like functions or classes.
Assignment statement: You assign a value to a variable.
Putting-in-the-pipeline statement: everything else except 1 and 2.
Example for definition statements:
Function foo($bar)
{
#do stuff here
}
Example for assignment statements:
$foo = 'bar'
Example for putting-in-the-pipeline statement:
It is exactly what you asked! If you write $a, then it will be written to the output pipeline. That’s it.
Now about Write-Output. According to this code from the official PowerShell repository, it's just a wrapper for another PowerShell Cmdlet, namely for WriteObject. Therefore, the invocation of Write-Output costs more time then the invocation of WriteObject.
As Lee_Dailey mentioned in the first comment to your question, there is a wonderful article Let’s Kill Write-Output written by Mark Kraus in his blog. At first sight it may seem that it doesn't have much to do with your question, but this article explains what happens with objects that you wrote in your script and when they are not surrounded with different "printing functions" like Write-Out. There you can also find examples of how to "bypass" the use of the Write-Out in different situations that it brings advantages in performance.
I also recommend to read these two articles from Microsoft's DevBlogs:
Understanding Streams, Redirection, and Write-Host in PowerShell
Weekend Scripter: Welcome to the PowerShell Information Stream
They will definitely help to understand how streams are implemented and how they work in PowerShell.