A function in PowerShell is a block of code that can be defined and then called by name. Functions can take input parameters and return output, just like a cmdlet. You can use functions to encapsulate a specific task or set of tasks, and then reuse that code multiple times in your script or on the command line. Here’s an example of a simple function in PowerShell:
function Get-Greeting {
param($Name)
"Hello, $Name!"
}The function keyword is used to define the start of the function, and the param keyword is used to define a parameter that the function expects as input. The body of the function is the code that will be executed when the function is called, in this case, a string with the greeting is returned.
To call this function, you would use the following syntax:
Get-Greeting -Name "John"This would output the string “Hello, John!” to the console.
You can also define multiple parameters for a function, like this:
function Get-Greeting {
param($FirstName, $LastName)
"Hello, $FirstName $LastName!"
}To call this function with multiple parameters, you would use the following syntax:
Get-Greeting -FirstName "John" -LastName "Doe"This would output the string “Hello, John Doe!” to the console.
You can make a parameter mandatory in a PowerShell function by using the [Parameter(Mandatory=$true)] attribute. For example, to make the $FirstName parameter mandatory in the Get-Greeting function, you would define the function like this:
function Get-Greeting {
[Parameter(Mandatory=$true)]
param($FirstName, $LastName)
"Hello, $FirstName $LastName!"
}Now, if you try to call the Get-Greeting function without specifying a value for the $FirstName parameter, you will get an error message telling you that the parameter is mandatory and you must provide a value.
Get-Greeting -LastName "Doe"This would produce an error message like “A parameter cannot be found that matches parameter name ‘FirstName’.”
You can use the ValidateSet attribute to specify a set of allowed values for a parameter in a PowerShell function. For example, to limit the $LastName parameter in the Get-Greeting function to a set of allowed values, you could define the function like this:
function Get-Greeting {
param($FirstName)
[ValidateSet("Doe", "Smith", "Jones")]
param($LastName)
"Hello, $FirstName $LastName!"
}Now, if you try to call the Get-Greeting function with a value for the $LastName parameter that is not in the set of allowed values, you will get an error message telling you that the value is not valid.
Get-Greeting -FirstName "John" -LastName "Brown"This would produce an error message like “The value of the parameter ‘LastName’ is invalid: Brown. Valid values are: Doe, Smith, Jones.”
You can also use the ValidateSet attribute to specify a set of allowed values that is stored in a variable or array. For example:
$AllowedLastNames = "Doe", "Smith", "Jones"
function Get-Greeting {
param($FirstName)
[ValidateSet($AllowedLastNames)]
param($LastName)
"Hello, $FirstName $LastName!"
}This would have the same effect as the previous example, but the set of allowed values is stored in the $AllowedLastNames variable rather than being hard-coded in the function definition.
In the previous example for piping, we are able to pipe multiple functions, first, Get-Process, then Where-Object, and into Sort-Object, finally calling Format-Table.
