Use variable for property name in calculated property

i writing code read xml file , dynamically generate report field names exported csv.  i've got working, except can't life of me figure out how use variable name reference property in expression select-object

i'm trying like:

			foreach ($entry in $xml')  			{  				$currentfieldset = @{  					name = $entry.objectname; expression = { $_.$($entry.$reportname) }  				}  				  			}  			$reportfieldmappings += $currentfieldset

later on i'd use $reportfieldmappings following:

$objects | select-object $reportfieldmappings | export-csv "c:\path\to\some\file.csv"

it has me absolutely stumped.  no matter in script block:

expression = { $_.$($entry.$reportname) }

i can't ever reference correct property name report.  i hope explanation makes sense.  i can provide more detail if necessary.  any appreciated!!

you try subexpression.

$_.$($reportname)

i've never attempted this, don't know if work or not.

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edit: seems work:

$propvar = 'lastwritetime'  get-item .\1.txt |     select name,@{n='test';e={$_.$($propvar)}}    name  test                  ----  ----                  1.txt 10/30/2015 8:48:08 am

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