How to export variables from a PowerShell module

Question

I've defined a variable in a psm1 file but when I try to access it in another script, after importing the module, I'm not seeing the value set in the psm1 file.

globals.psm1

$blah = "hello world"

my-script.ps1

Import-Module "$PSScriptRoot\globals.psm1" -Force -Verbose
Write-Output "blah: ${blah}"

output

PS C:\blah> .\my-script.ps1
VERBOSE: Loading module from path 'C:\blah\globals.psm1'.
blah: ''

I thought all variables get exported by default. I must be interrupting this wrong:

Specifies the variables that the module exports to the caller's session state. Wildcard characters are permitted. By default, all variables ('*') are exported

source: MSFT Docs -> How to write a PowerShell module manifest
(CTRL + F on 'VariablesToExport' to find the quoted text)

And yes, if I export the variable, I can access it but the documentation says: 'By default, all varialbes ('*') are exported so what am I doing wrong or misunderstanding? 🤔

globals.psm1

$blah = "hello world"
Export-ModuleMember -Variable blah

mklement0 · Accepted Answer · 2022-08-03 14:08:20Z

5

Your module is not using a module manifest (a companion .psd1 file whose RootModule entry points to your .psm1 file in the case of script modules), whereas the documentation you quote pertains to module manifest-based modules.

If a module consists only of a .psm1 file, and that file contains no Export-ModuleMember calls, the following rule applies:

Only functions and aliases are automatically exported.
Conversely, this means: in order to also export variables, you must use an Export-ModuleMember call - and if you do, the slate is wiped clean, so to speak, and you must explicitly specify all definitions you want to export (in the simplest case, use Export-ModuleMember -Function * -Alias * -Variable *).
Also, be sure to place this call at the end of your .psm1 file, to ensure that all definitions to export have already been defined.

Caveat, if a manifest (.psd1) is used:

The manifest's *ToExport keys apply on top of what the .psm1 file - implicitly or explicitly - exports, i.e. you can use it to further narrow what is to be exported, by explicitly enumerating the elements to export, which not only makes the module more self-describing, but also helps performance when PowerShell auto-discovers the commands in available, but not-(yet)-imported modules.
Therefore, if a manifest-based module wants to export variables, it too must have an explicit Export-ModuleMember call in its .psm1 file, with the manifest potentially narrowing down what variables are ultimately to be exported.

Generally, exporting variables from modules is best avoided, because:

it increases the risk of name collisions with variables of the same name defined elsewhere.
discovering which variables are exported by what module isn't as well-known as use of Get-Command is in order to determine what module a given function, cmdlet, or alias comes from. This is because (a) modules that export variables are rare and users generally don't expect it, and (b) the Get-Variable cmdlet - which can tell you what module a variable is defined in - isn't often used in practice.

To see which definitions a given module exports, pass -Verbose to the Import-Module call that imports it. Additionally, pass -Force in order to force re-loading of an already imported module.

edited Aug 3, 2022 at 14:08

answered Aug 3, 2022 at 2:29

mklement0

452k68 gold badges728 silver badges988 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

spottedmahn Over a year ago

"exporting variables from modules is best avoided", sure, I can see that 👍 but what's the "right" way to share some variables amongst some scripts 🤔? that's a rhetorical question as it's really a separate SO Q/A.

mklement0 Over a year ago

@spottedmahn: If you dot-source (load with . ) a .ps1 file (regular script file), you'll (indiscriminately) see all its definitions, including variables.

Collectives™ on Stack Overflow

How to export variables from a PowerShell module

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related