Utilizing parenthesis in Powershell

What exactly do parentheies do in Powershell?

Parenthesis serve numerous purposes in Powershell such as the following

• Arrays and Hash Tables
• Foreach, switch and If constructs/conditional statements
• Methods
• Subexpressions

Lets kick this article off with a few examples

What purpose do Parenthesis serve in Powershell? Think back to math class when we were taught order of operations,the math in between the (2+2) always needs to be done first. Powershell follows this rule the same way, lets start with a few examples.

Example 1

Say that we have a text file named computers.txt. This text file contains a few computer names we would like to restart using Powershell, the text file looks somewhat like this.

Text file containing computer names

Computer-01
Computer-02
Computer-03

Heres what the command would look like.

Restart-Computer -Computername (Get-Content -Path 'C:\Computerlist.txt')

Restart-Computer looks at the content loaded by the -Computername parameter, reads the computer names and begins restarting the machines listed in Computerlist.txt.

Example 2

For the next example, I am going to use the Get-Date cmdlet to calculate how many days,hours and even minutes have gone by since I was born.

(Get-Date) - (Get-Date 02/17/1993)

Output

Days              : 10844
Hours             : 16
Minutes           : 5
Seconds           : 5
Milliseconds      : 567
Ticks             : 9369795055672807
TotalDays         : 10844.670203325
TotalHours        : 260272.0848798
TotalMinutes      : 15616325.092788
TotalSeconds      : 936979505.567281
TotalMilliseconds : 936979505567.281

Looks like I have been alive a whopping 10,828 days! This example included loading two different dates using the Get-Date command, so how does this happen?

1. The content in the Get-Date commands surrounded by () get loaded first.
2. We use the - operator to subtract the first date from the second. The first date being the current date, the second being my birthday.

Example 3

This example is a trick I use to grab all of the parameters of a command.

(Get-command Get-Process).Parameters.Keys

Output

Name
Id
InputObject
IncludeUserName
Module
FileVersionInfo
Verbose
Debug
ErrorAction
WarningAction
InformationAction
ErrorVariable
WarningVariable
InformationVariable
OutVariable
OutBuffer
PipelineVariable

Here we are using Get-Command against the Get-Process cmdlet and enclosing it in Parenthesis. This gives us access to the parameters property which also holds a key property itself. For the next section we are going to dive into subexpressions which can come in pretty handy.

Working with subexpressions

Subexpressions are exactly what they sound like, an expression within an expression. What is an expression defined as? You can think of it as anything that we run in our terminal that provides us with an output/result. if you go to powershell right now and type out 2+2 you are using an expression. You could also write out "Two plus two equals four" which would also be considered an expression.

"Two plus two equals four" # This would give us output in the terminal exactly as it it written
"2+2" # This would provide us with the value four

Both of these expressions would work as they should, but what happens if we try to execute both of them within the same double quotes?

"Two plus two equals 2+2"

Unfortunately this would not work, Powershell would read this as the text value as is. This is where subexpressions come into play.

"Two plus two = $(2+2)"

Output

Two plus two = four

Now thats the output we were looking for, lets look at another example.

I find myself using subexpressions a lot with Get-Date . Lets create a log file with todays date using a subexpression.

We can start with the contents of the file. I will start by creating a variable containing the value I want to be in the file.

$Message = "The dog chased the red ball"

Now that we have the content for the log file, lets create the file itself.

 New-Item -Path "C:\Temp\TestLog-$(Get-Date -Format MM-dd-yy).txt" -Value $Message

Output

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---          10/27/2022  3:25 PM             27 TestLog-10-27-22.txt

Beautiful! The subexpression allowed us to incorporate todays date into the name of our log file. For fun lets inspect the content of the file using Get-Content

Get-Content -Path "C:\Temp\TestLog-10-27-22.txt"

Output

The Dog chased the red ball

Perfect, seems like everything is in order. I hope this article helped you achieve a better understanding of Parenthesis.

PoshDad signing off!