Importing a PowerShell Module

Artículo
09/17/2021

Once you have installed a module on a system, you will likely want to import the module. Importing is the process that loads the module into active memory, so that a user can access that module in their PowerShell session. In PowerShell 2.0, you can import a newly-installed PowerShell module with a call to Import-Module cmdlet. In PowerShell 3.0, PowerShell is able to implicitly import a module when one of the functions or cmdlets in the module is called by a user. Note that both versions assume that you install your module in a location where PowerShell is able to find it; for more information, see Installing a PowerShell Module. You can use a module manifest to restrict what parts of your module are exported, and you can use parameters of the Import-Module call to restrict what parts are imported.

Importing a Snap-In (PowerShell 1.0)

Modules did not exist in PowerShell 1.0: instead, you had to register and use snap-ins. However, it is not recommended that you use this technology at this point, as modules are generally easier to install and import. For more information, see How to Create a Windows PowerShell Snap-in.

Importing a Module with Import-Module (PowerShell 2.0)

PowerShell 2.0 uses the appropriately-named Import-Module cmdlet to import modules. When this cmdlet is run, Windows PowerShell searches for the specified module within the directories specified in the PSModulePath variable. When the specified directory is found, Windows PowerShell searches for files in the following order: module manifest files (.psd1), script module files (.psm1), binary module files (.dll). For more information about adding directories to the search, see about_PSModulePath. The following code describes how to import a module:

Import-Module myModule

Assuming that myModule was located in the PSModulePath, PowerShell would load myModule into active memory. If myModule was not located on a PSModulePath path, you could still explicitly tell PowerShell where to find it:

Import-Module -Name C:\myRandomDirectory\myModule -Verbose

You can also use the -Verbose parameter to identify what is being exported out of the module, and what is being imported into active memory. Both exports and imports restrict what is exposed to the user: the difference is who is controlling the visibility. Essentially, exports are controlled by code within the module. In contrast, imports are controlled by the Import-Module call. For more information, see Restricting Members That Are Imported, below.

Implicitly Importing a Module (PowerShell 3.0)

Beginning in Windows PowerShell 3.0, modules are imported automatically when any cmdlet or function in the module is used in a command. This feature works on any module in a directory that is included in the value of the PSModulePath environment variable. If you do not save your module on a valid path however, you can still load them using the explicit Import-Module option, described above.

The following actions trigger automatic importing of a module, also known as "module auto-loading."

Using a cmdlet in a command. For example, typing Get-ExecutionPolicy imports the Microsoft.PowerShell.Security module that contains the Get-ExecutionPolicy cmdlet.
Using the Get-Command cmdlet to get the command. For example, typing Get-Command Get-JobTrigger imports the PSScheduledJob module that contains the Get-JobTrigger cmdlet. A Get-Command command that includes wildcard characters is considered to be discovery and does not trigger importing of a module.
Using the Get-Help cmdlet to get help for a cmdlet. For example, typing Get-Help Get-WinEvent imports the Microsoft.PowerShell.Diagnostics module that contains the Get-WinEvent cmdlet.

To support automatic importing of modules, the Get-Command cmdlet gets all cmdlets and functions in all installed modules, even if the module is not imported into the session. For more information, see the help topic for the Get-Command cmdlet.

The Importing Process

When a module is imported, a new session state is created for the module, and a System.Management.Automation.PSModuleInfo object is created in memory. A session-state is created for each module that is imported (this includes the root module and any nested modules). The members that are exported from the root module, including any members that were exported to the root module by any nested modules, are then imported into the caller's session state.

The metadata of members that are exported from a module have a ModuleName property. This property is populated with the name of the module that exported them.

Warning

If the name of an exported member uses an unapproved verb or if the name of the member uses restricted characters, a warning is displayed when the Import-Module cmdlet is run.

By default, the Import-Module cmdlet does not return any objects to the pipeline. However, the cmdlet supports a PassThru parameter that can be used to return a System.Management.Automation.PSModuleInfo object for each module that is imported. To send output to the host, users should run the Write-Host cmdlet.

Restricting the Members That Are Imported

When a module is imported by using the Import-Module cmdlet, by default, all exported module members are imported into the session, including any commands exported to the module by a nested module. By default, variables and aliases are not exported. To restrict the members that are exported, use a module manifest. To restrict the members that are imported, use the following parameters of the Import-Module cmdlet.

Function: This parameter restricts the functions that are exported. (If you are using a module manifest, see the FunctionsToExport key.)
`Cmdlet: This parameter restricts the cmdlets that are exported (If you are using a module manifest, see the CmdletsToExport key.)
Variable: This parameter restricts the variables that are exported (If you are using a module manifest, see the VariablesToExport key.)
Alias: This parameter restricts the aliases that are exported (If you are using a module manifest, see the AliasesToExport key.)

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