about_Parameters
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