Compare-Object

Syntax

Compare-Object
       [-ReferenceObject] <PSObject[]>
       [-DifferenceObject] <PSObject[]>
       [-SyncWindow <Int32>]
       [-Property <Object[]>]
       [-ExcludeDifferent]
       [-IncludeEqual]
       [-PassThru]
       [-Culture <String>]
       [-CaseSensitive]
       [<CommonParameters>]

Description

The Compare-Object cmdlet compares two sets of objects. One set of objects is the reference, and the other set of objects is the difference.

The result of the comparison indicates whether a property value appeared only in the reference object (<=) or only in the difference object (=>). If the IncludeEqual parameter is used, (==) indicates the value is in both objects.

If the reference or the difference objects are null ($null), Compare-Object generates a terminating error.

Some examples use splatting to reduce the line length of the code samples. For more information, see about_Splatting. And, the examples use two text files, with each value on a separate line. Testfile1.txt contains the values: dog, squirrel, and bird. Testfile2.txt contains the values: cat, bird, and racoon.

Examples

Example 1: Compare the content of two text files

This example compares the contents of two text files. The output displays only the lines that are different between the files. Testfile1.txt is the reference object (<=) and Testfile2.txtis the difference object (=>).

Lines with content that appear in both files aren't displayed.

Compare-Object -ReferenceObject $(Get-Content -Path C:\Test\Testfile1.txt) -DifferenceObject $(Get-Content -Path C:\Test\Testfile2.txt)

InputObject SideIndicator
----------- -------------
cat         =>
racoon      =>
dog         <=
squirrel    <=

Example 2: Compare each line of content in two text files

This example uses the IncludeEqual to compare each line of content in two text files. All the lines of content from both files are displayed.

The SideIndicator specifies if the line appears in the Testfile1.txt reference object (<=), Testfile2.txt difference object (=>), or both files (==).

$objects = @{
ReferenceObject = $(Get-Content -Path C:\Test\Testfile1.txt)
DifferenceObject = $(Get-Content -Path C:\Test\Testfile2.txt)
}
Compare-Object @objects -IncludeEqual

InputObject SideIndicator
----------- -------------
bird        ==
cat         =>
racoon      =>
dog         <=
squirrel    <=

Example 3: Compare each line of content and exclude the differences

This example uses the IncludeEqual and ExcludeDifferent parameters to compare each line of content in two text files.

Because the command uses the ExcludeDifferent parameter, the output only contains lines contained in both files, as shown by the SideIndicator (==).

$objects = @{
ReferenceObject = $(Get-Content -Path C:\Test\Testfile1.txt)
DifferenceObject = $(Get-Content -Path C:\Test\Testfile2.txt)
}
Compare-Object @objects -IncludeEqual -ExcludeDifferent

InputObject SideIndicator
----------- -------------
bird        ==

Example 4: Compare two sets of process objects

This example compares two sets of objects that contain the computer's running processes.

$Processes_Before = Get-Process
notepad.exe
$Processes_After = Get-Process
Compare-Object -ReferenceObject $Processes_Before -DifferenceObject $Processes_After

InputObject                            SideIndicator
-----------                            -------------
System.Diagnostics.Process (notepad)   =>

The Get-Process cmdlet gets the computer's running processes and stores them in the $Processes_Before variable.

The notepad.exe application is started.

Get-Process gets the computer's updated list of running processes and stores them in the $Processes_After variable.

The Compare-Object compare the two sets of process objects stored in the $Processes_Before and $Processes_After variables. The output displays the difference, notepad.exe, from the $Processes_After object.

Parameters

-CaseSensitive

-Culture

-DifferenceObject

-ExcludeDifferent

-IncludeEqual

-PassThru

-Property

-ReferenceObject

-SyncWindow

Inputs

PSObject

You can send an object down the pipeline to the DifferenceObject parameter.

Outputs

None

If the reference object and the difference object are the same, there's no output.

PSCustomObject

If the objects are different, Compare-Object wraps the differing objects in a PSCustomObject wrapper with a SideIndicator property to reference the differences. When you use the PassThru parameter, Compare-Object omits the PSCustomObject wrapper around the compared objects and returns the differing objects, unchanged.

Related Links

• ForEach-Object
• Group-Object
• Measure-Object
• New-Object
• Select-Object
• Sort-Object
• Tee-Object
• Where-Object
• Get-Process