Why, in PowerShell, an installed module will be automatically imported when try to invoke a cmdlet in this module?

I'm a novice in PowerShell. I have encountered a problem with importing modules. It seems that an installed module will be automatically imported when I try to invoke a cmdlet in this module.

That's is:

If a module has been installed, such as Install-Module -Name PSscriptAnalyzer
Do not import it. Check it has not been imported:
```
Get-Module PSScriptAnalyzer
# Show nothing
```

Try to use a cmdlet in PSScriptAnalyzer:

Invoke-ScriptAnalyzer -Path ./ -Recurse
# Ignore any info

Then the module PSScriptAnalyzer will be automatically imported:

Get-Module PSScriptAnalyzer

It shows as the follows:

ModuleType Version    PreRelease Name                                
ExportedCommands
---------- -------    ---------- ----                                ----------------
Script     1.21.0                PSScriptAnalyzer                    {Get-ScriptAnalyzerRule, Invoke-Formatter, Invoke-ScriptAnalyzer}

Why will the module be imported automatically as long as its ExportedCommands have been imported? What is the mechanism it is? And if so, the Remove-Module doesn't seem to make much sense in general usage scenarios anymore.

Thanks in advance.

Solution

This is feature is called Module Auto-Loading and it was introduced in PowerShell 3.0:

PowerShell imports modules automatically the first time that you run any command in an installed module. You can now use the commands in a module without any set-up or profile configuration, so there's no need to manage modules after you install them on your computer.

And if so, the Remove-Module doesn't seem to make much sense in general usage scenarios anymore.

It is true that the cmdlet is rarely used however, Remove-Module still has its purpose, mainly for module development. The cmdlet is still viable when you need to test changes to your module without needing to restart the session (this is only true for non-binary modules, for binary modules you must restart the session, assemblies cannot be unloaded). Import-Module -Force also works for the same use case.

Another use case, also a rare one, is for modules that have a custom OnRemove callback. See Using the OnRemove event.