当null时，powershell强制性参数将引发错误

Question

I am confused about how to do error handling in the case that a mandatory variable remains null.

function parse-com{
    [CmdletBinding()]
    Param
    (
        [Parameter(Mandatory=$True)]
        [string[]]$list
     )
...

In this case if no argument is passed for $list then I am prompted for it, but if I just hit enter (pass a null to $list) then I throw an error. What I would rather do is throw a usage statement and/or exit gracefully. Example...

PS C:\Users\memyself> parse-com
cmdlet parse-com at command pipeline position 1
Supply values for the following parameters:
list[0]: 
parse-com : Cannot bind argument to parameter 'list' because it is an empty array.
At line:1 char:1
+ parse-com
+ ~~~~~~~~~
    + CategoryInfo          : InvalidData: (:) [parse-com], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyArrayNotAllowed,parse-com

Answer 1

When passing a $null value, that satisfies the Mandatory requirement. If you want the command then to fail prior to execution then you should use validation as @JeffZeitlin suggests.

It sounds like what you need to validate is that the value is not $null nor is it an empty array. For which you could user [ValidateNotNullOrEmpty()]

function parse-com{
    [CmdletBinding()]
    Param (
        [Parameter(Mandatory=$True)]
        [ValidateNotNullOrEmpty()]
        [string[]]$list
    )