I just ran into the most interesting behavior. I say that because I never ran into it before.
In many of my scripts I evaluate to see if a value has been passed in order to decide if I am going to process something.
Within my scripts it simply looks like this:
if ($VirtualMachineMigration) { }
If this parameter contains something, then act upon that something. The reverse is to use the not:
if (!$VirtualMachineMigration) { }
If this parameter contains nothing, then do something.
Today I learned that this works all well and fine with strings, and objects, and integers, etc. But not so well with Booleans.
Lets take a look at the following:
function EnableVMMigration
{
[CmdletBinding()]
param
(
[System.Boolean]
$VirtualMachineMigration
)
if ($VirtualMachineMigration) {
"in my If, making my next decision"
}
"Out of my IF"
}
That is simple enough, it accepts a Boolean parameter of VirtualMachineMigration. Lets give it a go:
First give it a $true:
PS C:\Users\Administrator\Documents> EnableVMMigration -VirtualMachineMigration $true
in my If, making my next decision
Out of my IF
Exactly as I expected.
Now, give it a $false
PS C:\Users\Administrator\Documents> EnableVMMigration -VirtualMachineMigration $false
Out of my IF
It never even entered my if statement. Because the If is $false, because I am sending it one – although the condition of the evaluation of ‘is $VirtualMachineMigration’ empty is actually no different than it was when it was $true.
So, what is happening? PowerShell is simply evaluating the parameter itself, not the question of ‘is this empty’.
Tricky little shell.
So, what if I really want to check if this is empty and the possibility is either $true or $false? (this is my first idea to work around this, I am sure that there are others)
So, lets update the function so that I truly see if the parameter is empty before deciding how to act on whether it is $true or $false
function EnableVMMigration
{
[CmdletBinding()]
param
(
[System.Boolean]
$VirtualMachineMigration
)
if ($VirtualMachineMigration) {
"making a positive choice"
}
elseif (!$VirtualMachineMigration) {
"Making a negative choice"
}
"Out of my IF"
}
PS C:\Users\Administrator\Documents> EnableVMMigration -VirtualMachineMigration $true
making a positive choice
Out of my IF
PS C:\Users\Administrator\Documents> EnableVMMigration -VirtualMachineMigration $false
Making a negative choice
Out of my IF
Now, that works the way I wanted it to.
