[问题求助] 求PowerShell解惑 dir 命令 加cd和不加cd的结果为什么不同

dir "W" -dir |
where{
	(dir $_.fullname -File -dep 2).name -contains "YES"
}
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gci task5 -File -rec  -include "YES"
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#@&cls&powershell "type '%~0'|out-string|iex"&pause&exit

[void][Reflection.Assembly]::LoadWithPartialName('System.Drawing')
cd "C:\Users\Administrator\Desktop\新建文件夹"
dir *.bmp |
foreach{
	$image = [Drawing.Image]::FromFile($_.FullName)
	#$image.Save($($_.BaseName + '.jpg'), [Drawing.Imaging.ImageFormat]::Jpeg)
	$s=$_.BaseName
	$image.Save("$s.jpg", [Drawing.Imaging.ImageFormat]::Jpeg)
	$image.Dispose()
}
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#@&cls&cd "C:\Users\Administrator\Desktop\新建文件夹"&powershell "type '%~0'|out-string|iex"&pause&exit

[void][Reflection.Assembly]::LoadWithPartialName('System.Drawing')

dir *.bmp |
foreach{
	$image = [Drawing.Image]::FromFile($_.FullName)
	#$image.Save($($_.BaseName + '.jpg'), [Drawing.Imaging.ImageFormat]::Jpeg)
	$s=$_.BaseName
	$image.Save("$s.jpg", [Drawing.Imaging.ImageFormat]::Jpeg)
	$image.Dispose()
}
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 https://docs.microsoft.com/zh-cn/powershell/module/microsoft.powershell.core/about/about_automatic_variables#pwd
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[void][Reflection.Assembly]::LoadWithPartialName('System.Drawing')
$a="C:\Users\Administrator\Desktop\新建文件夹"
[System.Environment]::CurrentDirectory=$a
cd $a
dir *.bmp |
foreach{
	$image = [Drawing.Image]::FromFile($_.FullName)
	#$image.Save($($_.BaseName + '.jpg'), [Drawing.Imaging.ImageFormat]::Jpeg)
	$s=$_.BaseName
	$image.Save("$s.jpg", [Drawing.Imaging.ImageFormat]::Jpeg)
	$image.Dispose()
}
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