Compare-Object

Compares two sets of objects.

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.

Compare-Object checks for available methods of comparing a whole object. If it can't find a suitable method, it call the ToString() methods of the input objects and compares the string results. You can provide one or more properties to be used for comparison. When properties are provided, the cmdlet compares the values of those properties only.

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.

Examples

Example 1 - Compare the content of two text files

This example compares the contents of two text files. The example uses the following 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.

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 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 3 - Show the difference when using the PassThru parameter

Normally, Compare-Object returns a PSCustomObject type with the following properties:

  • The InputObject being compared
  • The SideIndicator property showing which input object the output belongs to

When you use the PassThru parameter, the Type of the object is not changed but the instance of the object returned has an added NoteProperty named SideIndicator. SideIndicator shows which input object the output belongs to.

The following examples shows the different output types.

$a = $True
Compare-Object -IncludeEqual $a $a
(Compare-Object -IncludeEqual $a $a) | Get-Member

InputObject SideIndicator
----------- -------------
       True ==

   TypeName: System.Management.Automation.PSCustomObject
Name          MemberType   Definition
----          ----------   ----------
Equals        Method       bool Equals(System.Object obj)
GetHashCode   Method       int GetHashCode()
GetType       Method       type GetType()
ToString      Method       string ToString()
InputObject   NoteProperty System.Boolean InputObject=True
SideIndicator NoteProperty string SideIndicator===

Compare-Object -IncludeEqual $a $a -PassThru
(Compare-Object -IncludeEqual $a $a -PassThru) | Get-Member

True

   TypeName: System.Boolean
Name          MemberType   Definition
----          ----------   ----------
CompareTo     Method       int CompareTo(System.Object obj), int CompareTo(bool value), int IComparable.CompareTo(Syst
Equals        Method       bool Equals(System.Object obj), bool Equals(bool obj), bool IEquatable[bool].Equals(bool ot
GetHashCode   Method       int GetHashCode()
GetType       Method       type GetType()
GetTypeCode   Method       System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean     Method       bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte        Method       byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar        Method       char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime    Method       datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal     Method       decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble      Method       double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16       Method       short IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32       Method       int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64       Method       long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte       Method       sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle      Method       float IConvertible.ToSingle(System.IFormatProvider provider)
ToString      Method       string ToString(), string ToString(System.IFormatProvider provider), string IConvertible.To
ToType        Method       System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16      Method       ushort IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32      Method       uint IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64      Method       ulong IConvertible.ToUInt64(System.IFormatProvider provider)
TryFormat     Method       bool TryFormat(System.Span[char] destination, [ref] int charsWritten)
SideIndicator NoteProperty string SideIndicator===

When using PassThru, the original object type (System.Boolean) is returned. Note how the output displayed by the default format for System.Boolean objects didn't display the SideIndicator property. However, the returned System.Boolean object has the added NoteProperty.

Example 4 - Compare two simple objects using properties

In this example, we compare two different string that have the same length.

Compare-Object -ReferenceObject 'abc' -DifferenceObject 'xyz' -Property Length -IncludeEqual

Length SideIndicator
------ -------------
     3 ==

Example 5 - Comparing complex objects using properties

This example shows the behavior when comparing complex objects. In this example we store two different process objects for different instances of PowerShell. Both variables contain process objects with the same name. When the objects are compared without specifying the Property parameter, the cmdlet considers the objects to be equal. Notice that the value of the InputObject is the same as the result of the ToString() method. Since the System.Diagnostics.Process class does not have the IComparable interface, the cmdlet converts the objects to strings then compares the results.

PS> Get-Process pwsh

 NPM(K)    PM(M)      WS(M)     CPU(s)      Id  SI ProcessName
 ------    -----      -----     ------      --  -- -----------
    101   123.32     139.10      35.81   11168   1 pwsh
     89   107.55      66.97      11.44   17600   1 pwsh

PS> $a = Get-Process -Id 11168
PS> $b = Get-Process -Id 17600
PS> $a.ToString()
System.Diagnostics.Process (pwsh)
PS> $b.ToString()
System.Diagnostics.Process (pwsh)
PS> Compare-Object $a $b -IncludeEqual

InputObject                       SideIndicator
-----------                       -------------
System.Diagnostics.Process (pwsh) ==

PS> Compare-Object $a $b -Property ProcessName, Id, CPU

ProcessName    Id       CPU SideIndicator
-----------    --       --- -------------
pwsh        17600   11.4375 =>
pwsh        11168 36.203125 <>

When you specify properties to be compared, the cmdlet shows the differences.

Example 6 - Comparing complex objects that implement IComparable

If the object implements IComparable, the cmdlet searches for ways to compare the objects.If the objects are different types, the Difference object is converted to the type of the ReferenceObject then compared.

In this example, we are comparing a string to a TimeSpan object. In the first case, the string is converted to a TimeSpan so the objects are equal.

Compare-Object ([TimeSpan]"0:0:1") "0:0:1" -IncludeEqual

InputObject SideIndicator
----------- -------------
00:00:01    ==

Compare-Object "0:0:1" ([TimeSpan]"0:0:1")

InputObject SideIndicator
----------- -------------
00:00:01    =>
0:0:1       <>

In the second case, the TimeSpan is converted to a string so the object are different.

Parameters

-CaseSensitive

Indicates that comparisons should be case-sensitive.

Type:SwitchParameter
Position:Named
Default value:False
Accept pipeline input:False
Accept wildcard characters:False
-Culture

Specifies the culture to use for comparisons.

Type:String
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-DifferenceObject

Specifies the objects that are compared to the reference objects.

Type:PSObject[]
Position:1
Default value:None
Accept pipeline input:True
Accept wildcard characters:False
-ExcludeDifferent

Indicates that this cmdlet displays only the characteristics of compared objects that are equal. The differences between the objects are discarded.

Use ExcludeDifferent with IncludeEqual to display only the lines that match between the reference and difference objects.

If ExcludeDifferent is specified without IncludeEqual, there's no output.

Type:SwitchParameter
Position:Named
Default value:False
Accept pipeline input:False
Accept wildcard characters:False
-IncludeEqual

IncludeEqual displays the matches between the reference and difference objects.

By default, the output also includes the differences between the reference and difference objects.

Type:SwitchParameter
Position:Named
Default value:False
Accept pipeline input:False
Accept wildcard characters:False
-PassThru

When you use the PassThru parameter, Compare-Object omits the PSCustomObject wrapper around the compared objects and returns the differing objects, unchanged.

Type:SwitchParameter
Position:Named
Default value:False
Accept pipeline input:False
Accept wildcard characters:False
-Property

Specifies an array of properties of the reference and difference objects to compare.

The value of the Property parameter can be a new calculated property. The calculated property can be a script block or a hash table. Valid key-value pairs are:

  • Expression - <string> or <script block>

For more information, see about_Calculated_Properties.

Type:Object[]
Position:Named
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-ReferenceObject

Specifies an array of objects used as a reference for comparison.

Type:PSObject[]
Position:0
Default value:None
Accept pipeline input:False
Accept wildcard characters:False
-SyncWindow

Specifies the number of adjacent objects that Compare-Object inspects while looking for a match in a collection of objects. Compare-Object examines adjacent objects when it doesn't find the object in the same position in a collection. The default value is [Int32]::MaxValue, which means that Compare-Object examines the entire object collection.

Type:Int32
Position:Named
Default value:[Int32]::MaxValue
Accept pipeline input:False
Accept wildcard characters:False

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, unless you use the IncludeEqual parameter.

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, the Type of the object is not changed but the instance of the object returned has an added NoteProperty named SideIndicator. SideIndicator shows which input object the output belongs to.

Notes

When using the PassThru parameter, the output displayed in the console may not include the SideIndicator property. The default format view of the for the object type output by Compare-Object does not include the SideIndicator property. For more information see Example 3 in this article.