Why bother to use New-Variable?

Something pretty early on in your scripting experience you will have encountered is the assignment of a value to a variable. Most languages are pretty flexible in this and will allow some simple syntax like var = value. This sets a value that you want to reuse into memory and you access it again my making reference to the variable name that you chose. PowerShell is no different, running the command $Var = "Monday" will set the value Monday into memory and it can be recalled and used whenever you need it by using the variable name $Var1 in your script. This is pretty neat, compact, and simple to understand.

With this being so simple and probably suitable for most needs it isn’t often that people use New-Variable to do the same thing. In fact many people dont even know that there are a whole set of functions that work with variables. Let’s run a piece of code to find those commands. Run the command Get-Command -noun Variable and you will get results like below

Logically this all starts with New-Variable so let’s take a look at a couple of the parameters that this command has.

• -Name is pretty self explanatory and is mandatory - how else would we know how to get our data back ?!
• -Value again, it’s what we want to store so it’s mandatory
• -Description well that’s new. Perhaps we could add extra value to our code if we add a description of what a variable contains in addition to its name.
• -Option this is a mysterious and intriguing parameter and warrants further investigation

Using New-Variable is simple but take a close look, we don’t use a $ in front of the variable name when we use any of these commands.

New-Variable -Name StartDate -Value (Get-Date) -Description "To keep the date and time that we started"

There is no output from the command but if we reference the variable, with the leading $ then we see the date has been stored as we hoped. If we use the next logical command in the group Get-Variable by default we get some basic information - the variable name and the value it is set to but if we pass the output to Format-List we get a whole lot more information - there us that description that we set!

In order to investigate the -options parameter we will create a new variable.

New-Variable -Name Pi -Description "A constant value" -Value 3.141 -Option Readonly

Here we have created a new variable called $Pi and set it to a very short version of its value but we also used the -option parameter and declared the variable as ReadOnly. This means that we get an error if we try to set $Pi to a different value.

This could be really handy when you want to make sure no code edits misuse your variable for something else because they didnt fully appreciate how important it was. It is possible to change the value of a ReadOnly variable though, you just need to use Set-Variable and -Force.

So, this means that the variable is only going to be changed by someone who really needs to change it and that hopefully means that they also understand why they want to and that it wont affect your intentions elsewhere in the code.

It is possible however to stop even this sort of method making a change to a variable value.

New-Variable -Name Phi -Value 1.61803 -Description "Positive root of {x^{2}-x-1=0} ref https://en.wikipedia.org/wiki/List_of_mathematical_constants" -Option Constant

There is no way to change this variable value, you have to declare a new variable and use that or restart your PowerShell session and declare this variable with the desired value.

Not even the next command in the group Remove-Variable will affect a variable that has been declared as a constant.

The final command in this group is Clear-Variable, this is going to remove any value from the variable that it is used against, in the same way that you can set a variable to null with $Variable = $null.