Getting "System.Collections.Generic.List`1[System.String]" in CSV File export when data is okay on screen

arrays powershell csv stringify export-csv
G Beach picture G Beach · Mar 11, 2019 · Viewed 8.1k times · Source

I am new to PowerShell and trying to get a list of VM names and their associated IP Addresses from within Hyper-V.

I am getting the information fine on the screen but when I try to export to csv all I get for the IP Addresses is "System.Collections.Generic.List`1[System.String]" on each line.

There are suggestions about "joins" or "ConvertTo-CSV" but I don't understand the syntax for these.

Can anyone help?

This is the syntax I am using...

Get-VM | Select -ExpandProperty VirtualNetworkAdapters | select name, IPV4Addresses | Export-Csv -Path "c:\Temp\VMIPs.csv"

Answer

mklement0 picture mklement0 · Mar 11, 2019

If an object you export as CSV with Export-Csv or ConvertTo-Csv has property values that contain a collection (array) of values, these values are stringified via their .ToString() method, which results in an unhelpful representation, as in the case of your array-valued .IPV4Addresses property.

To demonstrate this with the ConvertTo-Csv cmdlet (which works analogously to Export-Csv, but returns the CSV data instead of saving it to a file):

PS> [pscustomobject] @{ col1 = 1; col2 = 2, 3 } | ConvertTo-Csv
"col1","col2"
"1","System.Object[]"

That is, the array 2, 3 stored in the .col2 property was unhelpfully stringified as System.Object[], which is what you get when you call .ToString() on a regular PowerShell array; other .NET collection types - such as [System.Collections.Generic.List[string]] in your case - stringify analogously; that is, by their type name.

Assuming you want to represent all values of an array-valued property in a single CSV column, to fix this problem you must decide on a meaningful string representation for the collection as a whole and implement it using Select-Object with a calculated property:

E.g., you can use the -join operator to create a space-separated list of the elements:

PS> [pscustomobject] @{ col1 = 1; col2 = 2, 3 } | 
      Select-Object col1, @{ n='col2'; e={ $_.col2 -join ' ' } } |
        ConvertTo-Csv
"col1","col2"
"1","2 3"

Note how array 2, 3 was turned into string '2 3'.

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