PowerShell Weekly
PowerShell Weekly

PoshBytes: Select-Object With Custom Properties (Because Plain Properties Are Boring)

Matthew Dowst

Today on PoshBytes, we are going to look at creating custom properties right in the pipeline with Select-Object.

This post is a companion for the video embedded below. Scroll down to see the code from the video.

Watch the video on YouTube PoshBytes: Select-Object With Custom Properties (Because Plain Properties Are Boring)

PoshBytes: Select-Object With Custom Properties (Because Plain Properties Are Boring)

Select-Object lets you choose and create custom properties directly in the pipeline.

Example with object properties

Select specific built-in properties.

Get-ChildItem C:\Temp | Select-Object Name, Length

Example with calculated property

Perform calculations directly in the pipeline.

Get-ChildItem C:\Temp | Select-Object Name, 
  {[math]::Round($_.Length / 1MB, 2)}

Example with calculated property and name

Label your calculated properties using Name and Expression.

Get-ChildItem C:\Temp | Select-Object Name, 
  @{Name='SizeMB';Expression={[math]::Round($_.Length / 1MB, 2)}}

Example with mixed data

Expressions can call any command, but not all should be used this way.

$Folder = 'C:\Temp'
Get-ChildItem $Folder | Select-Object Name, 
  @{Name='Folder';Expression={$Folder}},
  @{Name='QueryData';Expression={Get-Date}},
  @{Name='Content';Expression={Get-Content -Path $_.FullName}}

Example with error in Select-Object causing null output

Divide-by-zero errors inside expressions can produce null output without visible errors.

[math]::Round(1 / 0, 2)

Get-ChildItem C:\Temp | Select-Object Name, 
  @{Name='SizeMB';Expression={[math]::Round($_.Length / 0, 2)}}

Use Select-Object to display custom output, compute new columns, and name them clearly.

• Select-Object can calculate properties via script blocks.
• Use @{ Name = 'Column'; Expression = { … } } to add labels.
• Calculated expressions run per object.
• Great for formatting, math, and derived values.
• Errors inside Select-Object can yield empty output.

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