Windows Powershell过滤管道结果

PS C:Powershell> 1,2,1,2 | Get-Unique
1
2
1
2
PS C:Powershell> 1,2,1,2 | Sort-Object |Get-Unique
1
2
PS C:Powershell> ls | foreach{$_.extension} | Sort-Object |Get-Unique

.bat
.html
.ps1
.txt
.vbs
.xml