Adam Bertram shows how to write safer code by validating parameters:
Simply adding [Parameter()] to the parameter block makes this function “advanced.” Once we have this in place, we can then add in some parameter validation code. In our case, we need to ensure that the file provided with FilePath actually exists before proceeding. To do this, we’ll use the ValidateScript attribute which allows us to run any code we want. As long as it returns $true, it will allow the function to run.
function Set-File {
param(
[Parameter()]
[ValidateScript({ Test-Path -Path $_ -PathType Leaf})]
[string]$FilePath
)
}Notice that I used the pipeline variable $_ in this example. This represents whatever value the parameter is. If the user provides a file path that does not exist, they will be notified.
Read the whole thing.