Use value directly in script - powershell

Question

I have the following script. The issue i have is that i need to create a value before using the information gathered from the csv file. The first code is what works for me, the second code is how i would want to use it, where the value $uid is not create before
$users = import-csv c:\temp\users.csv
foreach ($user in $users){
$uid= $user.UserPrincipalName+":\calendar"
add-mailboxfolderpermission -identity $uid -user "calendar_reviewer" -AccessRights LimitedDetails
}
$users = import-csv c:\temp\users.csv
foreach ($user in $users){
add-mailboxfolderpermission -identity $user.UserPrincipalName+":\calendar" -user "calendar_reviewer" -AccessRights LimitedDetails
}

Answer 1

In short, your string composition isn't working like you're expecting it to.
If we use the following test function it'll demonstrate what's happening:
function Invoke-MyFunction
{
param( $Identity, $OtherParams )
write-host "identity = '$Identity'";
write-host "otherparams = '$OtherParams'";
}
In your first (working) example, PowerShell is concatenating the strings:
$uid = $user.UserPrincipalName+":\calendar"
Invoke-MyFunction -Identity $uid
# identity = 'myname:\calendar'
# otherparams = ''
but in your broken sample, it's not treating the $user.UserPrincipalName+":\calendar" as a single expression - it's treating +":\calendar" as a separate string that it passes as a second positional parameter:
Invoke-MyFunction -Identity $user.UserPrincipalName+":\calendar"
# identity = 'myname'
# otherparams = '+:\calendar'
There's a few different ways to get PowerShell to treat your parameter as an expression so it evaluates it before passing the value as a parameter:
Grouping Operator
As recommended by #zilog80 in the comments, wrap it in the Grouping operator (i.e. ( ... )) to force PowerShell to evaluate the expression before passing the result into the parameter:
Invoke-MyFunction -Identity ($user.UserPrincipalName+":\calendar")
# identity = 'myname:\calendar'
# otherparams = ''
String Interpolation
Per #Abraham Zinala's comment, use string interpolation (note the use of the Subexpression operator (i.e. $( ... ) to substitute in the value of $User.UserPrincipalName)
Invoke-MyFunction -Identity "$($User.UserPrincipalName):\calendar"
# identity = 'myname:\calendar'
# otherparams = ''
Assign to a variable
As you've already found, you can force the expression to be evaluated by assigning it to a temporary variable, then pass the variable as a parameter:
$uid = $user.UserPrincipalName+":\calendar"
Invoke-MyFunction -Identity $uid
# identity = 'myname:\calendar'
# otherparams = ''