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About methods

JuanPablo Jofre|Last Updated: 11/17/2016
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2 Contributors

about_methods

SHORT DESCRIPTION

Describes how to use methods to perform actions on objects in Windows PowerShell�.

LONG DESCRIPTION

Windows PowerShell uses objects to represent the items in data stores or the state of the computer. For example, FileInfo objects represent the files in file system drives and ProcessInfo objects represent the processes on the computer.

Objects have properties, which store data about the object, and methods that let you change the object.

A "method" is a set of instructions that specify an action you can perform on the object. For example, the FileInfo object includes the CopyTo method that copies the file that the FileInfo object represents.

To get the methods of any object, use the Get-Member cmdlet. Use its MemberType property with a value of "Method". The following command gets the methods of process objects.

PS C:\>Get-Process | Get-Member -MemberType Method
TypeName: System.Diagnostics.Process  

Name                      MemberType Definition  
----                      ---------- ----------  
BeginErrorReadLine        Method     System.Void BeginErrorReadLine()  
BeginOutputReadLine       Method     System.Void BeginOutputReadLine()  
...  
Kill                      Method     System.Void Kill()  
Refresh                   Method     System.Void Refresh()  
Start                     Method     bool Start()  
ToString                  Method     string ToString()  
WaitForExit               Method     bool WaitForExit(int milliseconds), System.Void WaitForExit()  
WaitForInputIdle          Method     bool WaitForInputIdle(int milliseconds), bool WaitForInputIdle()

To perform or "invoke" a method of an object, type a dot (.), the method name, and a set of parentheses "()". If the method has arguments, place the argument values inside the parentheses. The parentheses are required for every method call, even when there are no arguments.

For example, the following command invokes the Kill method of processes to end the Notepad process on the computer. As a result, the instance of Notepad closes. (The Get-Process command is enclosed in parentheses to insure that it runs before the Kill method is invoked.

(Get-Process Notepad).Kill()

Another very useful process is the Split method of strings. The split method takes a delimiter character argument that tells the method where to split the string.

PS C:\>$a = "Try-Catch-Finally"  
PS C:\>$a.Split("-")  
Try  
Catch  
Finally

As shown in the previous examples, you can invoke a method on an object that you get by using a command or an object in a variable.

Starting in Windows PowerShell 4.0, method invocation by using dynamic method names is supported.

LEARNING ABOUT METHODS

To find definitions of the methods of an object, go to help topic for the object type in MSDN and look for its methods page. For example, the following page describes the methods of process objects (System.Diagnostics.Process).

http://msdn.microsoft.com/library/system.diagnostics.process_methods

To determine the arguments of a method, review the method definition, which is like the syntax diagram of a Windows PowerShell cmdlet.

A method definition might have one or more method signatures, which are like the parameter sets of Windows PowerShell cmdlets. The signatures show all of the valid formats of commands to invoke the method.

For example, the CopyTo method of the FileInfo class contains the following two method signatures:

1. CopyTo(String destFileName)  
2. CopyTo(String destFileName, Boolean overwrite)

The first method signature takes the destination file name (and a path). The following example use The first CopyTo method to copy the Final.txt file to the C:\Bin directory.

(Get-ChildItem c:\final.txt).CopyTo("c:\bin\final.txt")

The second method signature take a destination file name and a Boolean value that determines whether the destination file should be overwritten, if it already exists.

The following example use The second CopyTo method to copy the Final.txt file to the C:\Bin directory, and to overwrite existing files.

(Get-ChildItem c:\final.txt).CopyTo("c:\bin\final.txt", $true)

METHODS OF SCALAR OBJECTS AND COLLECTIONS

The methods of one ("scalar") object of a particular type are often different from the methods of a collection of objects of the same type.

For example, every process has a Kill method, but a collection of processes does not have a Kill method.

Beginning in Windows PowerShell 3.0, Windows PowerShell tries to prevent scripting errors that result from the differing methods of scalar objects and collections.

Beginning in Windows PowerShell 4.0, collection filtering by using a method syntax is supported.

If you submit a collection, but request a method that exists only on single ("scalar") objects, Windows invokes the method on every object in the collection.

If the method exists on the individual objects and on the collection, Windows PowerShell does not alter the result.

This feature also works on properties of scalar objects and collections. For more information, see about_Properties.

EXAMPLES

The following example runs the Kill method of individual process objects on a collection of process objects. This example works only on Windows PowerShell 3.0 and later versions of Windows PowerShell.

The first command starts three instances of the Notepad process. The second command uses the Get-Process command to get all three instance of the Notepad process and save them in the $p variable.

PS C:\>Notepad; Notepad; Notepad  
PS C:\>$p = Get-Process Notepad

The third command uses the Count property of all collections to verify that there are three processes in the $p variable.

PS C:\>$p.Count  
3

The fourth command runs the Kill method on all three processes in the $p variable.

This command works even though a collection of processes does not have a Kill method.

PS C:\>$p.Kill()

The fifth command uses the Get-Process command to confirm that the Kill command worked.

PS C:\>Get-Process Notepad  
Get-Process : Cannot find a process with the name "notepad". Verify the process name and call the cmdlet again.  
At line:1 char:12  
+ get-process <<<<  notepad  
    + CategoryInfo          : ObjectNotFound: (notepad:String) [Get-Process], ProcessCommandException  
    + FullyQualifiedErrorId : NoProcessFoundForGivenName,Microsoft.PowerShell.Commands.GetProcessCommand

To perform the same task on Windows PowerShell 2.0, use the Foreach-Object cmdlet to run the method on each object in the collection.

PS C:\>$p | Foreach-Object {$_.Kill()}

SEE ALSO

about_Objects

about_Properties

Get-Member

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