powershell remote variables

Can anyone tell me why the following command creates the text file but does not populate it with any data?

Invoke-Command -ComputerName server1 -ScriptBlock {Set-Variable -Name wind -Value 'C:\Windows'}
Invoke-Command -ComputerName server1 -ScriptBlock {Get-ChildItem -Path $wind -name} | Out-File -FilePath C:\test\test.txt

but the following works fine and creates the data

Invoke-Command -ComputerName server1 -ScriptBlock {Get-ChildItem -Path C:\Windows -name} | Out-File -FilePath C:\test\test.txt
Dead_EyesAsked:
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footechCommented:
When you use Invoke-Command with the -computername parameter, it establishes a remote session and then terminates it as soon as the scriptblock is complete.  So the variable that you create in the first command no longer exists when you run the second command.  There are a few ways around this.  One is to create a session that will be used for each Invoke-command.  The session will persist until it is manually removed.
$s = New-PSSession -computername server1
Invoke-Command -session $s -ScriptBlock {Set-Variable -Name wind -Value 'C:\Windows'}
Invoke-Command -session $s -ScriptBlock {Get-ChildItem -Path $wind -name} | Out-File -FilePath C:\test\test.txt

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Another way is to create a scriptblock which contains all the commands you wish to run, and is executed by a single Invoke-Command command.
$block = { 
  Set-Variable -Name wind -Value 'C:\Windows'
  Get-ChildItem -Path $wind -name
}
Invoke-Command -ComputerName server1 -ScriptBlock $block | Out-File -FilePath C:\test\test.txt

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Or if the variable is from the local session and needs to be passed to the remote session.
Set-Variable -Name wind -Value 'C:\Windows'
Invoke-Command -ComputerName server1 -ScriptBlock {param ($wind) Get-ChildItem -Path $wind -name} -ArgumentList $wind | Out-File -FilePath C:\test\test.txt

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Dead_EyesAuthor Commented:
Excellent explanation and very helpful thanks
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