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ABOUT PARAMETERS
Short description
Describes how to work with command parameters in PowerShell.
Long description
Most PowerShell commands, such as cmdlets, functions, and scripts, rely on
parameters to allow users to select options or provide input. The
parameters follow the command name and have the following form:
-<parameter_name> <parameter_value>
-<parameter_name>:<parameter_value>
The name of the parameter is preceded by a hyphen (-), which signals to
PowerShell that the word following the hyphen is a parameter name. The
parameter name and value can be separated by a space or a colon character.
Some parameters do not require or accept a parameter value. Other
parameters require a value, but do not require the parameter name in the
command.
The type of parameters and the requirements for those parameters vary. To
find information about the parameters of a command, 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 script, use the full path to
the script file. For example:
Get-Help $home\Documents\Scripts\Get-Function.ps1
The Get-Help cmdlet returns various details about the command, including a
description, the command syntax, information about the parameters, and
examples showing how to use the parameters in a command.
You can also use the Parameter parameter of the Get-Help cmdlet to find
information about a particular parameter. Or, you can use the PARAMETER
parameter with the wildcard character ( * ) value to find information about
all parameters of the command. For example, the following command gets
information about all parameters of the Get-Member cmdlet:
Get-Help Get-Member -Parameter *
Default parameter values
Optional parameters have a default value, which is the value that is used
or assumed when the parameter is not specified in the command.
For example, the default value of the COMPUTERNAME parameter of many
cmdlets is the name of the local computer. As a result, the local computer
name is used in the command unless the COMPUTERNAME parameter is specified.
To find the default parameter value, see help topic for the cmdlet. The
parameter description should include the default value.
You can also set a custom default value for any parameter of a cmdlet or
advanced function. For information about setting custom default values, see
about_Parameters_Default_Values.
Parameter attribute table
When you use the FULL, PARAMETER, or ONLINE parameters of the Get-Help
cmdlet, Get-Help displays a parameter attribute table with detailed
information about the 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? 0
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, PowerShell
prompts you for a value for the parameter.
Parameter Position
If the Position setting is set to a positive integer, 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. A named parameter
can be listed in any position after the cmdlet name. 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
Position setting for PATH is 0, which means that it is a positional
parameter. The Position setting for EXCLUDE is NAMED.
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 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 must be placed in the order specified by the
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)", 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.
[!NOTE] A typed parameter that accepts pipeline input (by Value) or
(by PropertyName) enables use of DELAY-BIND script blocks on the
parameter.
The DELAY-BIND script block is run automatically during PARAMETERBINDING.
The result is bound to the parameter. Delay binding does NOT work for
parameters defined as type ScriptBlock or System.Object, the script block
is passed through WITHOUT being invoked.
You can read about DELAY-BIND script blocks here about_Script_Blocks.md
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, see about_CommonParameters.
See also
about_Command_syntax
about_Comment_Based_Help
about_Functions_Advanced
about_Parameters_Default_Values
about_Pipelines
about_Wildcards