about_Command_Syntax

บทความ
10/31/2023

Short description

Describes the syntax diagrams that are used in PowerShell.

Long description

The Get-Help and Get-Command cmdlets display syntax diagrams to help you construct commands correctly. This article explains how to interpret the syntax diagrams.

Get the syntax for a command

There are two ways to get the syntax for a command: Get-Help and Get-Command.

Get-Command

The Get-Command command can be used to get information about any command on your system. Use the Syntax parameter to get the syntax for a command.

Get-Command Get-Command -Syntax

Get-Command [[-ArgumentList] <Object[]>] [-Verb <string[]>] [-Noun <string[]>]
 [-Module <string[]>] [-FullyQualifiedModule <ModuleSpecification[]>]
 [-TotalCount <int>] [-Syntax] [-ShowCommandInfo] [-All] [-ListImported]
 [-ParameterName <string[]>] [-ParameterType <PSTypeName[]>]
 [<CommonParameters>]

Get-Command [[-Name] <string[]>] [[-ArgumentList] <Object[]>]
 [-Module <string[]>] [-FullyQualifiedModule <ModuleSpecification[]>]
 [-CommandType <CommandTypes>] [-TotalCount <int>] [-Syntax] [-ShowCommandInfo]
 [-All] [-ListImported] [-ParameterName <string[]>]
 [-ParameterType <PSTypeName[]>] [-UseFuzzyMatching]
 [-FuzzyMinimumDistance <uint>] [-UseAbbreviationExpansion]
 [<CommonParameters>]

Get-Help

The Get-Help command provides detailed information about PowerShell commands including, syntax, detailed description of the cmdlet and parameters, and examples. The output Get-Help command starts with a brief description of the command followed by the syntax.

Get-Help Get-Command

The following output has been shortened to focus on the syntax description.

NAME
    Get-Command

SYNOPSIS
    Gets all commands.

SYNTAX

    Get-Command [[-Name] <System.String[]>] [[-ArgumentList] <System.Object[]>]
    [-All] [-CommandType {Alias | Function | Filter | Cmdlet | ExternalScript |
    Application | Script | Workflow | Configuration | All}]
    [-FullyQualifiedModule <Microsoft.PowerShell.Commands.ModuleSpecification[]>]
    [-ListImported] [-Module <System.String[]>] [-ParameterName <System.String[]>]
    [-ParameterType <System.Management.Automation.PSTypeName[]>]
    [-ShowCommandInfo] [-Syntax] [-TotalCount <System.Int32>]
    [-UseAbbreviationExpansion] [-UseFuzzyMatching] [<CommonParameters>]

    Get-Command [[-ArgumentList] <System.Object[]>] [-All]
    [-FullyQualifiedModule <Microsoft.PowerShell.Commands.ModuleSpecification[]>]
    [-ListImported] [-Module <System.String[]>] [-Noun <System.String[]>]
    [-ParameterName <System.String[]>]
    [-ParameterType <System.Management.Automation.PSTypeName[]>]
    [-ShowCommandInfo] [-Syntax] [-TotalCount <System.Int32>]
    [-Verb <System.String[]>] [<CommonParameters>]
...

The output of Get-Help is slightly different from the output of Get-Command. Notice the difference in the syntax for the CommandType parameter. Get-Command shows the parameter type as the [CommandTypes] enumeration, while Get-Help show the possible values for the enumeration.

Parameter Sets

The parameters of a PowerShell command are listed in parameter sets. A PowerShell command can have one or more parameter sets. The Get-Command cmdlet has two parameter sets, as shown in the previous examples.

Some of the cmdlet parameters are unique to a parameter set, and others appear in multiple parameter sets. Each parameter set represents the format for a valid command. A parameter set includes only parameters that can be used together in a command. When parameters can't be used in the same command, they are listed in separate parameter sets.

For example, the Get-Random cmdlet has the following parameter sets:

$cmd = Get-Command Get-Random
$cmd.ParameterSets |
    Select-Object Name, IsDefault, @{n='Parameters';e={$_.ToString()}} |
    Format-Table -Wrap

Name                       IsDefault Parameters
----                       --------- ----------
RandomNumberParameterSet        True [[-Maximum] <Object>] [-SetSeed <int>]
                                     [-Minimum <Object>] [-Count <int>]
                                     [<CommonParameters>]
RandomListItemParameterSet     False [-InputObject] <Object[]> [-SetSeed <int>]
                                     [-Count <int>] [<CommonParameters>]
ShuffleParameterSet            False [-InputObject] <Object[]> -Shuffle
                                     [-SetSeed <int>] [<CommonParameters>]

The first parameter set returns one or more random numbers and has the Minimum, Maximum, and Count parameters.
The second parameter set returns a randomly selected object from a set of objects and includes the InputObject and Count parameters.
The third parameter set has the Shuffle parameter that returns a collection of objects in a random order, like shuffling a deck of cards.
All parameter sets have the SetSeed parameter and the common parameters.

These parameter sets show that you can use the InputObject and Count parameters in the same command, but you can't use the Maximum and Shuffle parameters together.

Every cmdlet also has a default parameter set. The default parameter set is used when you don't specify parameters that are unique to a parameter set. For example, if you use Get-Random without parameters, PowerShell assumes that you're using the RandomNumberParameterSet parameter set and it returns a random number.

Symbols in Syntax Diagrams

The syntax diagram lists the command name, the command parameters, and the parameter values.

The syntax diagrams use the following symbols:

A hyphen - indicates a parameter name. In a command, type the hyphen immediately before the parameter name with no intervening spaces, as shown in the syntax diagram.

For example, to use the Name parameter of Get-Command, type: Get-Command -Name.

Angle brackets < > indicate placeholder text. You don't type the angle brackets or the placeholder text in a command. Instead, you replace it with the item that it describes.

The placeholder inside the angle brackets identifies the .NET type of the value that a parameter takes. For example, to use the Name parameter of the Get-Command cmdlet, you replace the <string[]> with one or more strings separated by commas (,).

Brackets [] appended to a .NET type indicate that the parameter can accept one or more values of that type. Enter the values as a comma-separated list.

For example, the Name and Value parameters of the New-Alias cmdlet only take one string each.
```
New-Alias [-Name] <string> [-Value] <string>
```
```
New-Alias -Name MyAlias -Value mycommand.exe
```
But the Name parameter of Get-Process can take one or more strings.
```
Get-Process [-Name] <string[]>
```
```
Get-Process -Name Explorer, Winlogon, Services
```
Parameters with no values

Some parameters don't accept input, so they don't have a parameter value. Parameters without values are switch parameters. Switch parameters are used like boolean values. They default to $false. When you use a switch parameter, the value is set to $true.

For example, the ListImported parameter of Get-Command is a switch parameter. When you use the ListImported parameter, the cmdlet return only commands that were imported from modules in the current session.
```
Get-Command [-ListImported]
```

Brackets [ ] around parameters indicate optional items. A parameter and its value can be optional. For example, the CommandType parameter of Get-Command and its value are enclosed in brackets because they're both optional.
```
Get-Command [-CommandType <CommandTypes>]
```
Brackets around the parameter name, but not the parameter value, indicate that the parameter name is optional. These parameters are known as positional parameters. The parameter values must be presented in the correct order for the values to be bound to the correct parameter.

For example, for the New-Alias cmdlet, the Name and Value parameter values are required, but the parameter names, -Name and -Value, are optional.
```
New-Alias [-Name] <string> [-Value] <string>
```
```
New-Alias MyAlias mycommand.exe
```
In each parameter set, the parameters appear in position order. The order of parameters in a command matters only when you omit the optional parameter names. When parameter names are omitted, PowerShell assigns values to parameters by position and type. For more information about parameter position, see about_Parameters.
Braces {} indicate an "enumeration," which is a set of valid values for a parameter.

The values in the braces are separated by vertical bars |. These bars indicate an exclusive-OR choice, meaning that you can choose only one value from the set of values that are listed inside the braces.

For example, the syntax for the New-Alias cmdlet includes the following value enumeration for the Option parameter:
```
New-Alias -Option {None | ReadOnly | Constant | Private | AllScope}
```
The braces and vertical bars indicate that you can choose any one of the listed values for the Option parameter, such as ReadOnly or AllScope.
```
New-Alias -Option ReadOnly
```

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