使用Compare-Object比较两个集合，然后使用内部的.Where()扩展方法根据条目是否只在a.csv中找到将结果分为两个：

$a = Import-Csv path\to\a.csv
$b = Import-Csv path\to\b.csv

$outputs = @(
  # compare the two files, output everything, then split based on side-indicator
  Compare-Object $a $b -IncludeEqual
).Where({$_.SideIndicator -ne '<='}, 'Split')

# first collection will be the ones that satisfied `{$_.SideIndicator -ne '<='}`
$outputs[0] |ForEach-Object InputObject |Export-Csv output1.csv -NoTypeInformation
# second collection will be the ones that didn't, eg. the ones only found in a.csv
$outputs[1] |ForEach-Object InputObject |Export-Csv output2.csv -NoTypeInformation

如果你想输出到3个不同的文件，我建议在侧边指示器上使用Group-Object分组：

Compare-Object $a $b -IncludeEqual |Group-Object SideIndicator |ForEach-Object {
  # determine name of output file based on indicator
  $outputNames = @{'<='='a_only.csv';'=='='both.csv';'=>'='b_only.csv'}
  $outputName = $outputNames[$_.Group[0].SideIndicator]

  $_.Group |ForEach-Object InputObject |Export-Csv $outputName -NoTypeInformation
}