A Reference variable is used to pass values into a function.
By default, PowerShell variables are created with a "Local" scope, so a variable definition like $myvar = 'Hello World' will be visible only to the current script or the current function.
A reference variable ( defined with type: [ref]) is able to change the value of another variable that is passed to it. This means that you can write a function that directly modifies one, (or more likely several) existing variables, rather than just returning a value.
PS C:\> function add5([ref]$num)
>> $num.value = $num.value + 5
PS C:> $testing = 2
PS C:> $testing
PS C> add5 ([ref]$testing)
PS C> $testing
# Extending this to modify two variables:
PS> function add5minus5([ref]$add,[ref]$minus)
>> $add.value = $add.value + 5
>> $minus.value = $minus.value - 5
If the parameter passed is not a reference variable, an InvalidArgument exception will be thrown. The parameters passed must also match the type required, integer, string etc.
“To take the measure of oneself by reference to one’s colleagues leads to envy or complacency rather than constructive self-examination” ~ Benno C. Schmidt, Jr.
Related PowerShell Cmdlets:
How-to: Variables and Operators - Create variable, add to value, subtract, divide.
How-to: Environment variables - Windows environment variables Env:
Set-PSBreakpoint - Set a breakpoint on a line, command, or variable.
New-Variable - Allows a choice of "Global", "Local", "Private" or "Script".
Get-Variable - Get a PowerShell variable.
Set-Variable - Set a variable and a value.