I was helping someone with a profile script. The script is supposed to connect to a remote Exchange 2010 server using PowerShell v2.0 when it is launched.<\/p>\n
The script had a function which is called upon when profile is loaded. The function looked like the following:<\/p>\n
\nfunction connect-remotely()\n\n{\n if ($server)\n {\n $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http:\/\/$server\/PowerShell\/ -Authentication Kerberos\n Import-PSSession $Session\n write-warning 'Do not forget to run Remove-PSSession $Session'\n }\n else\n {\n $server = read-host \"Server name\"\n connect-remotely $server\n }\n}\n<\/pre>\nThe $session variable in this instance gets created and populated within the function. The problem, however, is not visible until a bit later. When we were done with our remote session, we tried to remove session using Remove-PSSession $session but encountered an error which indicated that $session has null value.<\/p>\n
Why did that happen? That\u2019s where I needed to understand how scopes work. The PowerShell session is created when we launch PowerShell. When the function is executed, a child scope is created. The $session variable is created within child scope. All is fine until after the function completes execution and exits. At this time, $session variable value becomes null since the scope in which it was created is no longer applicable.<\/p>\n
But wait, don\u2019t we need the object stored in that variable to remove session successfully? We sure do. So how do we address this?<\/p>\n
This can be accomplished using one of the two ways:<\/p>\n
1. Define the variable as global. This will make the variable available in all scopes including the one created by function and the parent scopes. Here\u2019s how you can do it:<\/p>\n
\n$Global:Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http:\/\/$server\/PowerShell\/ -Authentication Kerberos\n<\/pre>\n2. Second option (I like it better) is to define scope. I used New-Variable as describe below when creating $session within function and scoping it to value of 1:<\/p>\n
\nNew-Variable -Name Session -Value (New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http:\/\/$server\/PowerShell\/ -Authentication Kerberos) -Scope 1\n<\/pre>\nWhen you scope any variable, value 0 means the scope in which it was created. 1 means parent scope, 2 is grand parent and so on. By defining scope of 1, I made the variable available to parent scope of the function which is where I was running Remove-PSSession. As anyone can guess, both methods allowed me to successfully remove session as the variable $session stayed behind populated instead of becoming null.<\/p>\n