Powershell : Use a Select-Object expression with a string

Question

For some scripts, i need to have an output composed of calculated properties.

For example, for a list of ip addresses in ip.txt, i want to know if they respond to ping. So i try the following command:

Get-Content .\ip.txt | Select-Object $_,@{Name="ping?";Expression={Test-Connection $_ -Quiet -Count 1}}

But i get an error, regardless of what i do in the scriptblock expression.

The error (in french, sorry):

Select-Object : Paramètre Null. Le type attendu doit être l'un des suivants : {System.String, System.Management.Automation.ScriptBlock}. Au niveau de ligne : 1 Caractère : 37 + Get-Content .\ip.txt | Select-Object <<<< $_,@{Name="ping?";Expression={Test-Connection $_ -Quiet -Count 1}} + CategoryInfo : InvalidArgument: (:) [Select-Object], NotSupportedException + FullyQualifiedErrorId : DictionaryKeyUnknownType,Microsoft.PowerShell.Commands.SelectObjectCommand

I used the "calculated properties" in some scripts before, but with directories objects. Why it doesnt work with strings?

CB. · Accepted Answer · 2013-06-04 15:00:19Z

21

try this instead, you need to create calculated properties for each value:

Get-Content .\ip.txt | Select-Object  @{n="Server IP";e={$_}},@{n="ping?";e={[bool](Test-Connection $_ -Quiet -Count 1)}}

The problem in your code is the $_ not the calculated property. Select-object accept and array of properties, if in the array you pass $_ isn't evaluated as a property. If you do just select-object $_ (as select-object -prop $null ) piped items are the output.

edited Jun 4, 2013 at 15:00

answered Jun 4, 2013 at 14:50

CB.

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3 Comments

plunkets Over a year ago

Thanks! I tried "select-object $_" with success too, so i believed that the problem was the calculated property for a string object.

Chris F Carroll Over a year ago

So the gotcha here is that {n="label"; e=$_ } will fail but putting $_ inside braces succeeds: {n="label"; e={$_ }} ? Similarly for other expressions, e=expression will often fail, it has to be e={expression}

Chris F Carroll Over a year ago

The docs example on the magical @{n=;e=} syntax for projections show but don't tell : learn.microsoft.com/en-us/powershell/module/…

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