How to save a table to a log file without replacing the information

Question

I am trying to get a shadow storage information from remote computers. I could get the information and store in a variable as table.

But every time the log file is being overwrite by the new information.

My script:

$computerList = Get-Content "C:\Check_ShadowStorage\ServersList.txt"
foreach($computer in $computerList)
{
    $a = Invoke-Command -ComputerName $computer -Credential $credential -ScriptBlock {@(vssadmin list shadowstorage | Select-String -Context 0,5 '^Shadow Copy Storage' | 
Select @{Label="Shadow Copy Storage"; Expression={$_.Line.Trim("'").SubString(12)}}, 
   @{Label="Volume"; Expression={$_.Context.PostContext[0].Trim().SubString(13,2)}},
   @{Label="Used Shadow Copy"; Expression={$_.Context.PostContext[2].Trim().SubString(32)}},
   @{Label="Allocated Shadow Copy"; Expression={$_.Context.PostContext[2].Trim().SubString(32)}},
   @{Label="Maximum Storage"; Expression={$_.Context.PostContext[4].Trim().SubString(35)}}) |
      Format-Table Volume, 'Used Shadow Copy', 'Allocated Shadow Copy', 'Maximum Storage'}

$a | Out-File "C:\Check_ShadowStorage\Output.log"
}

The output I am wishing to have is something like:

                       Server A
Volume Used Shadow Copy Allocated Shadow Copy Maximum Storage
------ ---------------- --------------------- ---------------
S:     0 bytes (0%)     0 bytes (0%)          89.3 GB (10%)  
D:     8.48 GB (0%)     8.48 GB (0%)          93.0 GB (10%)  
C:     4.97 GB (8%)     4.97 GB (8%)          5.83 GB (10%)  

                       Server B
Volume Used Shadow Copy Allocated Shadow Copy Maximum Storage
------ ---------------- --------------------- ---------------
S:     0 bytes (0%)     0 bytes (0%)          89.3 GB (10%)  
D:     8.48 GB (0%)     8.48 GB (0%)          93.0 GB (10%)  
C:     4.97 GB (8%)     4.97 GB (8%)          5.83 GB (10%) 

And so on.

Answer 1

The issue with your code is that you're overwriting your output file because:

$a | Out-File "C:\Check_ShadowStorage\Output.log"

Is inside the foreach instead of outside. To fix it, you could change the foreach for a ForEach-Object and use the pipeline:

$computerList | ForEach-Object {
    # no assignment to `$a` needed here
    Invoke-Command -ComputerName $_ -Credential $credential -ScriptBlock {
        # same code here
    }
} | Out-File 'C:\Check_ShadowStorage\Output.log'

What you should do instead is not use Format-Table, output objects from your Invoke-Command and then pass them to Export-Csv to have structured output instead of plain text files.

$computerList = Get-Content 'C:\Check_ShadowStorage\ServersList.txt'
Invoke-Command $computerList {
    vssadmin list shadowstorage |
        Select-String -Context 0, 5 '^Shadow Copy Storage' |
        ForEach-Object {
            [pscustomobject]@{
                'Volume'                = $_.Context.PostContext[0].Trim().SubString(13, 2)
                'Used Shadow Copy'      = $_.Context.PostContext[2].Trim().SubString(32)
                'Allocated Shadow Copy' = $_.Context.PostContext[2].Trim().SubString(32)
                'Maximum Storage'       = $_.Context.PostContext[4].Trim().SubString(35)
                'Shadow Copy Storage'   = $_.Line.Trim("'").SubString(12)
            }
        }
} | Select-Object PSComputerName, * -ExcludeProperty RunspaceId |
    Export-Csv C:\Check_ShadowStorage\Output.csv -NoTypeInformation