How can I pass a local variable to a script block

Question

I'm trying to retrieve the Filehash of a file, located in remote server using Invoke-Command. I'm running my scripts on powershell version 4. It works fine, when i give the full path as below:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash E:\test\testfile.zip -Algorithm SHA1 
}

The above command works. But I need to pass the file name via a variable as below:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash E:\test\$dest.zip -Algorithm SHA1 
}

I'm new to scripting and powershell. Please, help me with resolving this!

Answer 1

In PowerShell 4 (3+ actually) the easiest way is to use the Using scope modifier:

Invoke-Command -ComputerName winserver -ScriptBlock { 
    Get-FileHash E:\test\$Using:dest.zip -Algorithm SHA1 
}

For a solution that works with all versions:

Invoke-Command -ComputerName winserver -ScriptBlock { param($myDest) 
    Get-FileHash E:\test\$myDest.zip -Algorithm SHA1 
} -ArgumentList $dest

Answer 2

To complement briantist's helpful answer:

The script block passed to Invoke-Command is (as intended) executed on the remote machine, using the remote machine's variables by default.

Thus, in order to use a local variable (value), extra steps are needed (to put it differently: inside a script block executed remotely, you cannot just refer to local variables as you normally would, such as with $dest):

• PS v3+ offers the using: scope modifier for direct use of a local variable inside the script block - see briantist's first command.

  • Note that using: only works when Invoke-Command actually targets a remote machine.

• The only option that also works in earlier versions is to pass the local variable as a parameter to the script block. - see briantist's second command.

For more information, refer to Get-Help about_Remote_Variables or the docs online.