Import-Module -Prefix '' on a module with a Default Prefix defined does not remove the prefix

Prerequisites

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Steps to reproduce

Make a module, and set Prefix to 'Test'
Import-Module MyTestModule -Prefix ''
All commands will still have test prefix

This is because the prefix test checks for IsNullOrEmpty instead of just null.

            bool usePrefix = !string.IsNullOrEmpty(prefix);

As such it is impossible to override the prefix which affects the ability to write pester tests on modules, etc. and use the original function names so that things like references and go to definition work in IDEs like vscode.

Workaround

Make a secondary manifest that references the same module but does not have the prefix specified.

Expected behavior

Commands without prefix

Actual behavior

Commands have default prefix

Error details

No response

Environment data

PS 7.2.1

Visuals

No response

As alternative for discussion - introduce new parameter (-NoPrefix/-RemovePrefix).

Also question for discussion - is the prefix a strong contact from module author?

Ilya (@iSazonov)

Ilya (@iSazonov) I don't think it should be a strong contract. A "proper" module (at least script wise) I write as if it has no prefix, all the commands and references are of the non-prefixed version. If a prefix is specified, everything continues to work as expected. The user can specify multiple prefixes potentially and import the module multiple times to address multiple target scenarios, so they can use Get-SourceMyFunction and Get-DestinationMyFunction for instance if the connection context is kept at module scope.

I do think that the specified bool should not be IsNullOrEmpty but simply a null check, so that an empty '' can indicate I don't want a prefix, however I understand that is more breaking than -NoPrefix so I"m fine with that too.

My current main issue pain point here is in Pester Testing, the only way I can specify my pester test commands after importing the module is to make a completely different non-prefixed manifest, or use a prefix (but then in VSCode, my GoTo references no longer work). I want to use the same non-prefixed commands that I have defined during testing without having to make an entirely separate manifest file.

I made the following workaround, the regexes are fragile but it works for my use case

function Import-ModuleWithoutPrefix {
  [CmdletBinding()]
  param(
    [Parameter(Mandatory, ValueFromPipeline)]$ManifestPath,
    [Switch]$Force,
    $TempPath = 'TEMP:'
  )
  $path = Resolve-Path $ManifestPath
  $manifestDir = Split-Path $Path -Parent
  $fileName = [io.path]::GetFileNameWithoutExtension($path)
  #Manifest file name must be the same
  $tempPath = "TEMP:\$(New-Guid)\$fileName.psd1"

  $manifestContent = Get-Content -Raw $path
  $rootModuleRegex = '(?<=RootModule\s*?=\s*?[''"])(.+?)(?=[''"])'
  if ($manifestContent -notmatch $rootModuleRegex) {
    throw "Could not find RootModule entry in manifest $path"
  }
  $rootModulePath = [io.path]::IsPathRooted($matches[1]) ? $matches[1] : $(Join-Path $manifestDir $matches[1])
  $resolvedRootModulePath = Resolve-Path $rootModulePath
  $manifestContent = $manifestContent -replace $rootModuleRegex, $resolvedRootModulePath

  #Remove any prefix entry present. If this doesn't exist we don't error out
  $manifestContent = $manifestContent -replace 'DefaultCommandPrefix\s*?=\s*?[''"].+?[''"]'

  #This should be unique
  New-Item -ItemType File -Force -Path $tempPath -Value $manifestContent | Out-Null

  Write-Verbose "Importing module $path without prefix from $tempPath"
  Import-Module $tempPath -Force:$Force -PassThru
}

We rolled back PR with fix due to a regression. The code is not trivial and has low test coverage.
We need to add more tests for importing modules with/without (default) prefixes.
Prefix parameter is internally BasePrefix which is initialized with string.Empty. So we should change this to null. But BasePrefix is used in some code branches which should be reviewed and fixed with covering by tests.

Ilya (@iSazonov)

Ilya (@iSazonov) thanks for the investigation!

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Import-Module -Prefix '' on a module with a Default Prefix defined does not remove the prefix #16936

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Import-Module -Prefix '' on a module with a Default Prefix defined does not remove the prefix #16936

Description

Prerequisites

Steps to reproduce

Workaround

Expected behavior

Actual behavior

Error details

Environment data

Visuals

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iSazonov commented on Mar 2, 2022

JustinGrote commented on Mar 9, 2022

JustinGrote commented on Mar 10, 2022

iSazonov commented on Apr 28, 2025

JustinGrote commented on Apr 28, 2025

JustinGrote commented on Oct 27, 2025

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