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Select-Object

  • Reference
Module:
Microsoft.PowerShell.Utility

Selects objects or object properties.

Syntax

Select-Object
      [-InputObject <PSObject>]
      [[-Property] <Object[]>]
      [-ExcludeProperty <String[]>]
      [-ExpandProperty <String>]
      [-Unique]
      [-Last <Int32>]
      [-First <Int32>]
      [-Skip <Int32>]
      [-Wait]
      [<CommonParameters>]
Select-Object
      [-InputObject <PSObject>]
      [[-Property] <Object[]>]
      [-ExcludeProperty <String[]>]
      [-ExpandProperty <String>]
      [-Unique]
      [-SkipLast <Int32>]
      [<CommonParameters>]
Select-Object
      [-InputObject <PSObject>]
      [-Unique]
      [-Wait]
      [-Index <Int32[]>]
      [<CommonParameters>]

Description

The Select-Object cmdlet selects specified properties of an object or set of objects. It can also select unique objects, a specified number of objects, or objects in a specified position in an array.

To select objects from a collection, use the First, Last, Unique, Skip, and Index parameters. To select object properties, use the Property parameter. When you select properties, Select-Object returns new objects that have only the specified properties.

Beginning in Windows PowerShell 3.0, Select-Object includes an optimization feature that prevents commands from creating and processing objects that are not used.

When you include a Select-Object command with the First or Index parameters in a command pipeline, PowerShell stops the command that generates the objects as soon as the selected number of objects is generated, even when the command that generates the objects appears before the Select-Object command in the pipeline. To turn off this optimizing behavior, use the Wait parameter.

Examples

Example 1: Select objects by property

This command creates objects that have the Name, ID, and working set (WS) properties of process objects.

Get-Process | Select-Object -Property ProcessName, Id, WS

Example 2: Select objects by property and format the results

This command gets information about the modules used by the processes on the computer. It uses Get-Process cmdlet to get the process on the computer.

It uses the Select-Object cmdlet to output an array of [System.Diagnostics.ProcessModule] instances as contained in the Modules property of each System.Diagnostics.Process instance output by Get-Process.

The command uses the Property parameter of the Select-Object cmdlet to select the process names. This add a ProcessName NoteProperty to every [System.Diagnostics.ProcessModule] instance and populates it with the value of current processes ProcessName property.

The command uses the Format-List cmdlet to display the name and modules in of each process in a list.

Get-Process Explorer | Select-Object -Property ProcessName -ExpandProperty Modules | Format-List

ProcessName       : explorer
ModuleName        : explorer.exe
FileName          : C:\WINDOWS\explorer.exe
BaseAddress       : 140697278152704
ModuleMemorySize  : 3919872
EntryPointAddress : 140697278841168
FileVersionInfo   : File:             C:\WINDOWS\explorer.exe
                    InternalName:     explorer
                    OriginalFilename: EXPLORER.EXE.MUI
                    FileVersion:      10.0.17134.1 (WinBuild.160101.0800)
                    FileDescription:  Windows Explorer
                    Product:          Microsoft Windows Operating System
                    ProductVersion:   10.0.17134.1
...

Example 3: Select processes using the most memory

This command gets the five processes that are using the most memory. The Get-Process cmdlet gets the processes on the computer. The Sort-Object cmdlet sorts the processes according to memory (working set) usage, and the Select-Object cmdlet selects only the last five members of the resulting array of objects.

The Wait parameter is not required in commands that include the Sort-Object cmdlet because Sort-Object processes all objects and then returns a collection. The Select-Object optimization is available only for commands that return objects individually as they are processed.

Get-Process | Sort-Object -Property WS | Select-Object -Last 5

Handles  NPM(K)    PM(K)      WS(K) VS(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
2866     320       33432      45764   203   222.41   1292 svchost
577      17        23676      50516   265    50.58   4388 WINWORD
826      11        75448      76712   188    19.77   3780 Ps
1367     14        73152      88736   216    61.69    676 Ps
1612     44        66080      92780   380   900.59   6132 INFOPATH

Example 4: Select unique characters from an array

This command uses the Unique parameter of Select-Object to get unique characters from an array of characters.

"a","b","c","a","a","a" | Select-Object -Unique

a
b
c

Example 5: Select newest and oldest events in the event log

These commands gets the first (newest) and last (oldest) events in the Windows PowerShell event log.

The command uses the Get-EventLog cmdlet to get all events in the Windows PowerShell log. It saves them in the $a variable.

The second command uses a pipeline operator (|) to send the events in $a to the Select-Object cmdlet. The Select-Object command uses the Index parameter to select events from the array of events in the $a variable. The index of the first event is 0. The index of the last event is the number of items in $a minus 1.

$a = Get-EventLog -LogName "Windows PowerShell"
$a | Select-Object -Index 0, ($A.count - 1)

Example 6: Select all but the first object

This command creates a new PSSession on each of the computers listed in the Servers.txt files, except for the first one.

This command uses the Select-Object cmdlet to select all but the first computer in a list of computer names. The resulting list of computers is set as the value of the ComputerName parameter of the New-PSSession cmdlet.

New-PSSession -ComputerName (Get-Content Servers.txt | Select-Object -Skip 1)

Example 7: Rename files and select several to review

This command adds a "-ro" suffix to the base names of text files that have the read-only attribute and then displays the first five files so the user can see a sample of the effect.

The command uses the ReadOnly dynamic parameter of the Get-ChildItem for FileSystem cmdlet to get read-only files. It uses a pipeline operator (|) to send the files to the Rename-Item cmdlet, which renames the file. It uses the Passthru parameter of Rename-Item to send the renamed files to the Select-Object cmdlet, which selects the first 5 for display.

The Wait parameter of Select-Object prevents PowerShell from stopping the Get-ChildItem cmdlet after it gets the first five read-only text files. Without this parameter, only the first five read-only files would be renamed.

Get-ChildItem *.txt -ReadOnly | Rename-Item -NewName {$_.BaseName + "-ro.txt"} -PassThru | Select-Object -First 5 -Wait

Example 8: Demonstrate the intricacies of the -ExpandProperty parameter

This example demonstrates the intricacies of the ExpandProperty parameter.

Note that the output generated was an array of [System.Int32] instances. The instances conform to standard formatting rules of the Output View. This is true for any Expanded properties. If the outputted objects have a specific standard format, the expanded property might not be visible.

# Create a custom object to use for the Select-Object example.
$object = [pscustomobject]@{Name="CustomObject";Expand=@(1,2,3,4,5)}
# Use the ExpandProperty parameter to Expand the property.
$object | Select-Object -ExpandProperty Expand -Property Name

1
2
3
4
5

# The output did not contain the Name property, but it was added successfully.
# Use Get-Member to confirm the Name property was added and populated.
$object | Select-Object -ExpandProperty Expand -Property Name | Get-Member

TypeName: System.Int32

Name        MemberType   Definition
----        ----------   ----------
CompareTo   Method       int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(System.Object obj)...
Equals      Method       bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
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       int16 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(string format), string ToString(System.IFormatProvider provider)...
ToType      Method       System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method       uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method       uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method       uint64 IConvertible.ToUInt64(System.IFormatProvider provider)
Name        NoteProperty string Name=CustomObject

Example 9: Create custom properties on objects

The following example demonstrates using Select-Object to add a custom property to any object. When you specify a property name that does not exist, Select-Object creates that property as a NoteProperty on each object passed.

$customObject = 1 | Select-Object -Property MyCustomProperty
$customObject.MyCustomProperty = "New Custom Property"
$customObject

MyCustomProperty
----------------
New Custom Property

Example 10: Create calculated properties for each InputObject

This example demonstrates using Select-Object to add calculated properties to your input. Passing a ScriptBlock to the Property parameter causes Select-Object to evaluate the expression on each object passed and add the results to the output. Within the ScriptBlock, you can use the $_ variable to reference the current object in the pipeline.

By default, Select-Object will use the ScriptBlock string as the name of the property. Using a Hashtable, you can label the output of your ScriptBlock as a custom property added to each object. You can add multiple calculated properties to each object passed to Select-Object.

# Create a calculated property called $_.StartTime.DayOfWeek
Get-Process | Select-Object -Property ProcessName,{$_.StartTime.DayOfWeek}

ProcessName  $_.StartTime.DayOfWeek
----         ----------------------
alg                       Wednesday
ati2evxx                  Wednesday
ati2evxx                   Thursday
...

# Add a custom property to calculate the size in KiloBytes of each FileInfo object you pass in.
# Use the pipeline variable to divide each file's length by 1 KiloBytes
$size = @{label="Size(KB)";expression={$_.length/1KB}}
# Create an additional calculated property with the number of Days since the file was last accessed.
# You can also shorten the key names to be 'l', and 'e', or use Name instead of Label.
$days = @{l="Days";e={((Get-Date) - $_.LastAccessTime).Days}}
# You can also shorten the name of your label key to 'l' and your expression key to 'e'.
Get-ChildItem $PSHOME -File | Select-Object Name, $size, $days

Name                        Size(KB)        Days
----                        --------        ----
Certificate.format.ps1xml   12.5244140625   223
Diagnostics.Format.ps1xml   4.955078125     223
DotNetTypes.format.ps1xml   134.9833984375  223

Parameters

-ExcludeProperty

Specifies the properties that this cmdlet excludes from the operation. Wildcards are permitted. This parameter is effective only when the command also includes the Property parameter.

Type:String[]
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:True

-ExpandProperty

Specifies a property to select, and indicates that an attempt should be made to expand that property.

  • If the specified property is an array, each value of the array is included in the output.
  • If the specified property is an object, the objects properties are expanded for every InputObject

In either case, the Type of objects output will match the Type of the expanded property.

If the Property parameter is specified, Select-Object will attempt to add each selected property as a NoteProperty to every outputted object.

Warning

If you receive the error: Select : Property cannot be processed because property <PropertyName> already exists, consider the following. Note that when using -ExpandProperty, Select-Object can not replace an existing property. This means:

  • If the expanded object has a property of the same name, an error will occur.
  • If the Selected object has a property of the same name as an Expanded objects property, an error will occur.
Type:String
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-First

Specifies the number of objects to select from the beginning of an array of input objects.

Type:Int32
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-Index

Selects objects from an array based on their index values. Enter the indexes in a comma-separated list.

Indexes in an array begin with 0, where 0 represents the first value and (n-1) represents the last value.

Type:Int32[]
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-InputObject

Specifies objects to send to the cmdlet through the pipeline. This parameter enables you to pipe objects to Select-Object.

When you pass objects to the InputObject parameter, instead of using the pipeline, Select-Object treats the InputObject as a single object, even if the value is a collection. It is recommended that you use the pipeline when passing collections to Select-Object.

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

-Last

Specifies the number of objects to select from the end of an array of input objects.

Type:Int32
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-Property

Specifies the properties to select. These properties are added as NoteProperty members to the output objects. Wildcards are permitted.

The value of the Property parameter can be a new calculated property. To create a calculated, property, use a hash table. Valid keys are:

  • Name (or Label): <string>
  • Expression <string> or <script block>
Type:Object[]
Position:0
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:True

-Skip

Skips (does not select) the specified number of items. By default, the Skip parameter counts from the beginning of the array or list of objects, but if the command uses the Last parameter, it counts from the end of the list or array.

Unlike the Index parameter, which starts counting at 0, the Skip parameter begins at 1.

Type:Int32
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-SkipLast

Skips (does not select) the specified number of items from the end of the list or array. Works in the same way as using Skip together with Last parameter.

Unlike the Index parameter, which starts counting at 0, the SkipLast parameter begins at 1.

Type:Int32
Position:Named
Default value:None
Required:False
Accept pipeline input:False
Accept wildcard characters:False

-Unique

Specifies that if a subset of the input objects has identical properties and values, only a single member of the subset will be selected.

This parameter is case-sensitive. As a result, strings that differ only in character casing are considered to be unique.

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

-Wait

Indicates that the cmdlet turns off optimization. PowerShell runs commands in the order that they appear in the command pipeline and lets them generate all objects. By default, if you include a Select-Object command with the First or Index parameters in a command pipeline, PowerShell stops the command that generates the objects as soon as the selected number of objects is generated.

This parameter was introduced in Windows PowerShell 3.0.

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

Inputs

PSObject

You can pipe any object to Select-Object.

Outputs

PSObject

Notes

  • You can also refer to the Select-Object cmdlet by its built-in alias, select. For more information, see about_Aliases.
  • The optimization feature of Select-Object is available only for commands that write objects to the pipeline as they are processed. It has no effect on commands that buffer processed objects and write them as a collection. Writing objects immediately is a cmdlet design best practice. For more information, see Write Single Records to the Pipeline in Strongly Encouraged Development Guidelines in the MSDN library.