About Requires

Short description

Prevents a script from running without the required elements.

Long description

The #Requires statement prevents a script from running unless the Windows PowerShell version, modules, snap-ins, module and snap-in version, and edition prerequisites are met. If the prerequisites are not met, Windows PowerShell does not run the script.

Syntax

#Requires -Version <N>[.<n>]
#Requires -PSSnapin <PSSnapin-Name> [-Version <N>[.<n>]]
#Requires -Modules { <Module-Name> | <Hashtable> }
#Requires -PSEdition <PSEdition-Name>
#Requires -ShellId <ShellId>
#Requires -RunAsAdministrator

Rules for use

  • A script can include more than one #Requires statement.

  • The #Requires statements can appear on any line in a script.

    Placing a #Requires statement inside a function does NOT limit its scope. All #Requires statements are always applied globally, and must be met, before the script can execute.

    Warning

    Even though a #Requires statement can appear on any line in a script, its position in a script does not affect the sequence of its application.

    The global state the #Requires statement presents must be met before script execution.

    Example:

    Get-Module Hyper-V | Remove-Module
    #Requires -Modules Hyper-V
    

    You might think that the above code should not run because the required module was removed before the #Requires statement. However, the #Requires state had to be met before the script could even execute. Then the first line of the script invalidated the required state.

Parameters

-Version <N>[.<n>]

Specifies the minimum version of Windows PowerShell that the script requires. Enter a major version number and optional minor version number.

For example:

#Requires -Version 3.0

-PSSnapin <PSSnapin-Name> [-Version <N>[.<n>]]

Specifies a Windows PowerShell snap-in that the script requires. Enter the snap-in name and an optional version number.

For example:

#Requires -PSSnapin DiskSnapin -Version 1.2

-Modules <Module-Name> | <Hashtable>

Specifies Windows PowerShell modules that the script requires. Enter the module name and an optional version number. The Modules parameter is introduced in Windows PowerShell 3.0.

If the required modules are not in the current session, Windows PowerShell imports them. If the modules cannot be imported, Windows PowerShell throws a terminating error.

For each module, type the module name (<String>) or a hash table with the following keys. The value can be a combination of strings and hash tables.

  • ModuleName - [Required] Specifies the module name.
  • GUID - [Optional] Specifies the GUID of the module.
  • It is also Required to specify one of the two below keys, they cannot be used together.
    • ModuleVersion - [Required] Specifies a minimum acceptable version of the module.
    • RequiredVersion - [Required] Specifies an exact, required version of the module.

Note

RequiredVersion was added in Windows PowerShell 5.0.

For example:

Require that Hyper-V (version 1.1 or greater) is installed.

#Requires -Modules @{ ModuleName="Hyper-V"; ModuleVersion="1.1" }

Requires that Hyper-V (only version 1.1) is installed.

#Requires -Modules @{ ModuleName="Hyper-V"; RequiredVersion="1.1" }

Requires that any version of PSScheduledJob and PSWorkflow, is installed.

#Requires -Modules PSWorkflow, PSScheduledJob

When using the RequiredVersion key, ensure your version string exactly matches the version string you wish to require.

Get-Module Hyper-V
ModuleType Version    Name     ExportedCommands
---------- -------    ----     ------------------
Binary     2.0.0.0    hyper-v  {Add-VMAssignableDevice, ...}

This will FAIL, because "2.0.0" does not exactly match "2.0.0.0"

#Requires -Modules @{ ModuleName="Hyper-V"; RequiredVersion="2.0.0" }

-PSEdition <PSEdition-Name>

Specifies a PowerShell edition that the script requires. Valid values are Core for PowerShell Core and Desktop for Windows PowerShell.

For example:

#Requires -PSEdition Core

-ShellId

Specifies the shell that the script requires. Enter the shell ID.

For example:

#Requires -ShellId MyLocalShell

You can find current ShellId by querying $ShellId automatic variable.

-RunAsAdministrator

When this switch parameter is added to your requires statement, it specifies that the Windows PowerShell session in which you are running the script must be started with elevated user rights (Run as Administrator). The RunAsAdministrator parameter is introduced in Windows PowerShell 4.0.

For example:

#Requires -RunAsAdministrator

Examples

The following script has two #Requires statements. If the requirements specified in both statements are not met, the script does not run. Each #Requires statement must be the first item on a line:

#Requires -Modules PSWorkflow
#Requires -Version 3
Param
(
    [parameter(Mandatory=$true)]
    [String[]]
    $Path
)
...

Notes

In Windows PowerShell 3.0, the Windows PowerShell Core packages appear as modules in sessions started by using the InitialSessionState.CreateDefault2 method, such as sessions started in the Windows PowerShell console. Otherwise, they appear as snap-ins. The exception is Microsoft.PowerShell.Core, which is always a snap-in.

See also

about_Automatic_Variables

about_Language_Keywords

about_PSSnapins

Get-PSSnapin