Would like to automate this Powershell command that sets the UPN of all mail enabled users

Question

I have command that changes the UPN of all mailbox users
Get-ADUser -Filter * -properties homemdb | where {$_.homemdb -ne $null} | ForEach-Object ($_.SamAccountName) {$CompleteUPN = $_.SamAccountName + “@contoso.com”; Set-ADUser -Identity $_.DistinguishedName -UserPrincipalName $CompleteUPN}
The command works using the AD module for
powershell. What I would like to do it write a script that does the following.
Runs the command above
Only applies changes to users that need it. (I think this applies the setting to all users with the "homemdb")
I was thinking of setting it as a scheduled task on one of the Domain Controllers. My
powershell skills are lacking at best, so any guidance on how to set this up would be much appreciated. 
Thanks

Answer 1

Cannot bind parameter 'Filter' to the target.
Exception setting "Filter":
"Invalid filter syntax. For a description of
the filter parameter syntax see the command help.
"(RecipientType -eq
'UserMailbox') -and
(UserPrincipalName -notlike
('*@{1}' -f $UPNSuffix))" at position 68."
    + CategoryInfo         
: WriteError:
(:) [Get-User],
ParameterBindingException
    + FullyQualifiedErrorId
: ParameterBindingFailed,Microsoft.Exchange.Management.RecipientTasks.GetUser
Read the error very carefully: "Invalid filter syntax"
You filter: "(RecipientType -eq
'UserMailbox') -and
(UserPrincipalName -notlike
('*@{1}' -f $UPNSuffix))"
This is not a good filter for anything.
This is not legal in a filter: (UserPrincipalName
-notlike ('*@{1}'
-f $UPNSuffix))"
See filter syntax for rules on the limited support for PowerShell syntax.   filters are a subset.
¯\_(ツ)_/¯