About methods
Short description
Describes how to use methods to perform actions on objects in PowerShell.
Long description
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.
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), ...
WaitForInputIdle Method bool WaitForInputIdle(int millisecon...
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. If the method takes multiple arguments, they should be separated by commas.
For example, the following command invokes the Kill method of processes to end the Notepad process on the computer.
$notepad = Get-Process notepad
$notepad.Kill()
This example can be shortened by combining the above statements.
(Get-Process Notepad).Kill()
The Get-Process command is enclosed in parentheses to ensure that it
runs before the Kill method is invoked. The Kill method is then invoked
on the returned Process object.
Another very useful method is the Replace method of strings. The Replace
method, replaces text within a string. In the example below, the dot (.) can
be placed immediately after the end quote of the string.
'this is rocket science'.Replace('rocket', 'rock')
this is rock science
As shown in the previous examples, you can invoke a method on an object that you get by using a command, an object in a variable, or anything that results in an object (like a string in quotes).
Starting in 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.
To determine the arguments of a method, review the method definition, which is like the syntax diagram of a PowerShell cmdlet.
A method definition might have one or more method signatures, which are like the parameter sets of 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:
CopyTo(String destFileName)
CopyTo(String destFileName, Boolean overwrite)
The first method signature takes the destination file name (and a path). The
following example uses 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")
Note
Unlike PowerShell's argument mode, object methods execute in expression mode, which is a pass-through to the .NET framework that PowerShell is built on. In expression mode bareword arguments (unquoted strings) are not allowed. You can see this in the difference path as a parameter, versus the path as an argument. You can read more about parsing modes in about_Parsing
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 uses 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 PowerShell 3.0, PowerShell tries to prevent scripting errors that result from the differing methods of scalar objects and collections.
If you submit a collection, but request a method that exists only on single ("scalar") objects, PowerShell invokes the method on every object in the collection.
If the method exists on the individual objects and on the collection, only the collection's method is invoked.
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 PowerShell 3.0 and later versions of 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.
Notepad; Notepad; Notepad
$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.
$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.
$p.Kill()
The fifth command uses the Get-Process command to confirm that the Kill
command worked.
Get-Process Notepad
Get-Process : Cannot find a process with the name "notepad". Verify the proc
ess name and call the cmdlet again.
At line:1 char:12
+ Get-Process <<<< notepad
+ CategoryInfo : ObjectNotFound: (notepad:String) [Get-Process]
, ProcessCommandException
+ FullyQualifiedErrorId : NoProcessFoundForGivenName,Microsoft.PowerShel
l.Commands.GetProcessCommand
To perform the same task on PowerShell 2.0, use the Foreach-Object cmdlet to
run the method on each object in the collection.
$p | ForEach-Object {$_.Kill()}
ForEach and Where methods
Beginning in PowerShell 4.0, collection filtering by using a method syntax is
supported. This allows use of two new methods when dealing with collections
ForEach and Where.
You can read more about these methods in about_arrays