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Get-Unique

  • Reference
Module:
Microsoft.PowerShell.Utility

Returns unique items from a sorted list.

Syntax

Get-Unique
   [-InputObject <PSObject>]
   [-AsString]
   [-CaseInsensitive]
   [<CommonParameters>]
Get-Unique
   [-InputObject <PSObject>]
   [-OnType]
   [-CaseInsensitive]
   [<CommonParameters>]

Description

The Get-Unique cmdlet compares each item in a sorted list to the next item, eliminates duplicates, and returns only one instance of each item. The list must be sorted for the cmdlet to work properly.

By default, Get-Unique is case-sensitive. As a result, strings that differ only in character casing are considered to be unique.

Examples

Example 1: Get unique words in a text file

These commands find the number of unique words in a text file.

$A = $( foreach ($line in Get-Content C:\Test1\File1.txt) {
    $line.tolower().split(" ")
  }) | Sort-Object | Get-Unique
$A.count

The first command gets the content of the File.txt file. It converts each line of text to lowercase letters and then splits each word onto a separate line at the space (" "). Then, it sorts the resulting list alphabetically (the default) and uses the Get-Unique cmdlet to eliminate any duplicate words. The results are stored in the $A variable.

The second command uses the Count property of the collection of strings in $A to determine how many items are in $A.

Example 2: Get unique integers in an array

This command finds the unique members of the set of integers.

1,1,1,1,12,23,4,5,4643,5,3,3,3,3,3,3,3 | Sort-Object | Get-Unique

1
3
4
5
12
23
4643

The first command takes an array of integers typed at the command line, pipes them to the Sort-Object cmdlet to be sorted, and then pipes them to Get-Unique, which eliminates duplicate entries.

Example 3: Get unique object types in a directory

This command uses the Get-ChildItem cmdlet to retrieve the contents of the local directory, which includes files and directories.

Get-ChildItem | Sort-Object {$_.GetType()} | Get-Unique -OnType

The pipeline operator (|) sends the results to the Sort-Object cmdlet. The $_.GetType() statement applies the GetType method to each file or directory. Then, Sort-Object sorts the items by type. Another pipeline operator sends the results to Get-Unique. The OnType parameter directs Get-Unique to return only one object of each type.

Example 4: Get unique processes

This command gets the names of processes running on the computer with duplicates eliminated.

Get-Process | Sort-Object | Select-Object processname | Get-Unique -AsString

The Get-Process command gets all of the processes on the computer. The pipeline operator (|) passes the result to Sort-Object, which, by default, sorts the processes alphabetically by ProcessName. The results are piped to the Select-Object cmdlet, which selects only the values of the ProcessName property of each object. The results are then piped to Get-Unique to eliminate duplicates.

The AsString parameter tells Get-Unique to treat the ProcessName values as strings. Without this parameter, Get-Unique treats the ProcessName values as objects and returns only one instance of the object, that is, the first process name in the list.

Example 5: Use case-sensitive comparisons to get unique strings

This example uses case-insensitive comparisons to get unique strings from an array of strings.

"aa", "Aa", "Bb", "bb", "aa" | Sort-Object -CaseSensitive | Get-Unique

aa
Aa
bb
Bb

Example 6: Use case-insensitive comparisons to get unique strings

This example uses case-insensitive comparisons to get unique strings from an array of strings.

"aa", "Aa", "Bb", "bb", "aa" | Sort-Object | Get-Unique -CaseInsensitive

aa
Bb

Parameters

-AsString

Indicates that this cmdlet uses the data as a string. Without this parameter, data is treated as an object, so when you submit a collection of objects of the same type to Get-Unique, such as a collection of files, it returns just one (the first). You can use this parameter to find the unique values of object properties, such as the file names.

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

-CaseInsensitive

By default, Get-Unique is case-sensitive. When you use this parameter, the cmdlet uses case-insensitive comparisons.

This parameter was added in PowerShell 7.4.

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

-InputObject

Specifies input for Get-Unique. Enter a variable that contains the objects or type a command or expression that gets the objects.

This cmdlet treats the input submitted using InputObject as a collection. It doesn't enumerate individual items in the collection. Because the collection is a single item, input submitted using InputObject is always returned unchanged.

Type:PSObject
Position:Named
Default value:None
Required:False
Accept pipeline input:True
Accept wildcard characters:False

-OnType

Indicates that this cmdlet returns only one object of each type.

Type:SwitchParameter
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

Inputs

PSObject

You can pipe any type of object to this cmdlet.

Outputs

PSObject

This cmdlet returns its input objects without duplicates.

Notes

PowerShell includes the following aliases for Get-Unique:

  • All platforms:
    • gu

For more information, see about_Aliases.

To sort a list, use Sort-Object. You can also use the Unique parameter of Sort-Object to find the unique items in a list.