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about_Parameters

Updated: May 20, 2009

Applies To: Windows PowerShell 2.0

TOPIC
    about_Parameters

SHORT DESCRIPTION
    Describes how to work with cmdlet parameters in Windows PowerShell. 


LONG DESCRIPTION
    Most Windows PowerShell cmdlets and functions rely on parameters to allow
    users to select options or provide input. The parameters follow the cmdlet 
    or function name and typically have the following form:


        -<parameter_name> <parameter_value>


    The name of the parameter is preceded by a hyphen (-), which signals to 
    Windows PowerShell that the word following the hyphen is a parameter and 
    not a value being passed to the cmdlet or function. Not all parameters 
    require a value, and not all parameter names must be specified. In some 
    cases, the parameter name is implied and does not need to be included in 
    the command.

    
    The type of parameters and the requirements for those parameters vary by 
    cmdlet and by function from cmdlet to cmdlet. To find information about the
    parameters of a cmdlet, use the Get-Help cmdlet. For example, to find 
    information about the parameters of the Get-ChildItem cmdlet, type:


        get-help get-childitem


    To find information about the parameters of a function, review the 
    parameter definitions. Parameters are defined either after the function 
    name or inside the body of the function, using the Param keyword. For more 
    information, see about_Functions.


    Some functions also contain comment-based Help about parameters. Use the 
    Get-Help cmdlet with these functions. For more information, see the help 
    topic for Get-Help and about_Comment_Based_Help. 


    The Get-Help Cmdlet returns various details about the cmdlet or function, 
    including a description of the cmdlet or function, the command syntax, 
    information about the parameters, and examples showing how to use the 
    cmdlet or function.
 

    You can also use the Parameter parameter of the Get-Help cmdlet or function 
    to find information about a particular parameter. Or, you can use the 
    wildcard character (*) with the Parameter parameter to find information 
    about all the parameters of the cmdlet or function. For example, the 
    following command gets information about all the parameters of the 
    Get-Member cmdlet or function:


        get-help get-member -parameter *


    This information includes the details you need to know to use the 
    parameter. For example, the Help topic for the Get-ChildItem cmdlet 
    includes the following details about its Path parameter:

        -path <string[]>
            Specifies a path of one or more locations. Wildcard characters are
            permitted. The default location is the current directory (.).

        Required?                    false
        Position?                    1
        Default value                Current directory
        Accept pipeline input?       true (ByValue, ByPropertyName)
        Accept wildcard characters?  true


    The parameter information includes the parameter syntax,
    a description of the parameter, and the parameter attributes.
    The following sections describe the parameter attributes.


  Parameter Required?
    This setting indicates whether the parameter is mandatory, that
    is, whether all commands that use this cmdlet must include this
    parameter. When the value is "True" and the parameter is missing
    from the command, Windows PowerShell prompts you for a value for
    the parameter.


  Parameter Position?
    This setting indicates whether you can supply a parameter's value 
    without preceding it with the parameter name. If set to "0" or "named," 
    a parameter name is required. This type of parameter is referred to as
    a named parameter. A named parameter can be listed in any position 
    after the cmdlet name.


    If the "Parameter position?" setting is set to an integer other than 0, 
    the parameter name is not required. This type of parameter is referred 
    to as a positional parameter, and the number indicates the position 
    in which the parameter must appear in relation to other positional 
    parameters. If you include the parameter name for a positional 
    parameter, the parameter can be listed in any position after the
    cmdlet name.


    For example, the Get-ChildItem cmdlet has Path and Exclude parameters. 
    The "Parameter position?" setting for Path is 1, which means that it
    is a positional parameter. The "Parameter position?" setting for Exclude
    is 0, which means that it is a named parameter. 


    This means that Path does not require the parameter name, but its
    parameter value must be the first or only unnamed parameter value
    in the command. However, because the Exclude parameter is a named 
    parameter, you can place it in any position in the command.


    As a result of the "Parameter position?" settings for these two 
    parameters, you can use any of the following commands:


        Get-ChildItem -path c:\techdocs -exclude *.ppt
        Get-ChildItem c:\techdocs -exclude *.ppt
        Get-ChildItem -exclude *.ppt -path c:\techdocs
        Get-ChildItem -exclude *.ppt c:\techdocs


    If you were to include another positional parameter without including 
    the parameter name, that parameter would have to be placed in the order 
    specified by the "Parameter position?" setting.


  Parameter Type
    This setting specifies the Microsoft .NET Framework type of the parameter 
    value. For example, if the type is Int32, the parameter value must be an
    integer. If the type is string, the parameter value must be a 
    character string. If the string contains spaces, the value must be 
    enclosed in quotation marks, or the spaces must be preceded by the 
    escape character (`).


  Default Value
    This setting specifies the value that the parameter will assume
    if no other value is provided. For example, the default value of
    the Path parameter is often the current directory. Required
    parameters never have a default value. For many optional parameters,
    there is no default because the parameter has no effect if it is
    not used. 


  Accepts Multiple Values?
    This setting indicates whether a parameter accepts multiple
    parameter values. When a parameter accepts multiple values,
    you can type a comma-separated list as the value of the parameter
    in the command, or save a comma-separated list (an array) in a
    variable, and then specify the variable as the parameter value.


    For example, the ServiceName parameter of the Get-Service
    cmdlet accepts multiple values. The following commands are both valid:


        get-service -servicename winrm, netlogon


        $s = "winrm", "netlogon"
        get-service -servicename $s


  Accepts Pipeline Input?
    This setting indicates whether you can use the pipeline operator
    (|) to send a value to the parameter. 

    
    Value                    Description
    -----                    -----------
    False                    Indicates that you cannot pipe a value to the 
                             parameter.


    True (by Value)          Indicates that you can pipe any value to the 
                             parameter, just so the value has the .NET 
                             Framework type specified for the parameter or the
                             value can be converted to the specified .NET 
                             Framework type.


                             When a parameter is "True (by Value)", Windows 
                             PowerShell tries to associate any piped values 
                             with that parameter before it tries other methods
                             to interpret the command.


    True (by Property Name)  Indicates that you can pipe a value to the 
                             parameter, but the .NET Framework type of the 
                             parameter must include a property with the same
                             name as the parameter.
 
                             For example, you can pipe a value to a Name 
                             parameter only when the value has a property 
                             called "Name".


  Accepts Wildcard Characters?
    This setting indicates whether the parameter's value can contain 
    wildcard characters so that the parameter value can be matched to more 
    than one existing item in the target container.


  Common Parameters
    Common parameters are parameters that you can use with any cmdlet.
    For more information, about common parameters, type:


        help about_commonparameters


SEE ALSO
    about_Command_syntax
    about_Comment_Based_Help
    about_Functions_Advanced
    about_Pipelines
    about_Wildcards



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