Selecting Objects & Properties (Select-Object)

Command Equivalents

Description

Select-Object is a highly versatile utility cmdlet with two primary, distinct functions:

1. Selecting Objects: It can select a specific number of objects from the beginning or end of a collection, similar to the head and tail commands.
2. Selecting Properties: It can reshape objects by selecting only specific properties, effectively creating a new, custom object with just the data you need. This is similar in concept to using cut or awk to pick specific columns of text.

Selecting a Subset of Objects

These parameters are used to filter the number of objects passing through the pipeline.

-First and -Last

These parameters grab the first or last N items from a collection.

# Get the 5 most CPU-intensive processes
Get-Process | Sort-Object -Property CPU -Descending | Select-Object -First 5

# Get the 10 most recent events from the System event log
Get-EventLog -LogName System -Newest 50 | Select-Object -Last 10

-Unique

This parameter returns only the unique items from a collection. When used with -Property, it returns objects that have unique values for that property.

# Get a unique list of all file extensions in a directory
Get-ChildItem -File -Recurse | Select-Object -Property Extension -Unique

-Skip

This parameter ignores the first N items and selects the rest. It’s often used with -First to create a “page” of results.

# Get processes 6 through 15 from a CPU-sorted list
Get-Process | Sort-Object CPU -Descending | Select-Object -Skip 5 -First 10

Selecting Specific Properties

The -Property parameter is used to create new objects that contain only the specified properties from the original objects.

Basic Property Selection

You can provide a comma-separated list of property names you want to keep.

# Display only the name, ID, and memory usage (Working Set) for all processes
Get-Process | Select-Object -Property ProcessName, Id, WS

Calculated Properties

This is a powerful feature that lets you add new, custom properties to the output object. This is done using a hash table with Name and Expression keys.

• Name: The name of your new custom property.
  • Expression: A script block ({...}) that calculates the value for the new property. Remember, $_ represents the current object.

# Select the file name and create a new property called 'SizeInMB'
Get-ChildItem -File |
  Select-Object -Property Name, @{Name="SizeInMB"; Expression={"{0:N2}" -f ($_.Length / 1MB)}}

In this example, for each file, we create a new property SizeInMB by taking its Length (in bytes), dividing by 1 megabyte, and then formatting it as a number with two decimal places ("{0:N2}" -f ...).