What is a module?

In its simplest form a module is a subfolder in one of the folders listed in $env:PSModulePath with a PowerShell script of the same name (but with the extension .psm1 instead of .ps1)

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You can see each of the folders listed in $env:PSModulePath by splitting it like this:

$env:PSModulePath | % {$_ -split ";"}

e.g. (I'll explain them all here)

C:\Users\MyUser\OneDrive\Documents\WindowsPowerShell\Modules		# Modules for *just me*
C:\Program Files\WindowsPowerShell\Modules											# Modules for all users
C:\Windows\system32\WindowsPowerShell\v1.0\Modules							# Modules that windows installed...

The .psm1 file ends with an Export-ModuleMember statement saying which functions and aliases to export., e.g.

Export-ModuleMember -Function Get-Foo, New-Bar, ... -Alias gf, ..

How to import a local .psm1 module file

If you have a module as a local .psm1 file, you can import it like this:

import-module cowsay.psm1

That will create a folder called cowsay (in this case), under one of the $env:PSModulePath folders mentioned above, and put the cowsay.psm1 file into it.

Normally you would instead import it from an online repository. And you may also want to know how to publish to one of those.

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See also