Easily call the SetDllDirectory Win32 API function from PowerShell

DllDirectoryManager.psm1

function addDllDirectoryManager {
    $csharp = @'
using System;
using System.Text;
using System.Runtime.InteropServices;
public static class DllDirectoryManager
{
    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool SetDllDirectory(string lpPathName);

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    private static extern uint GetDllDirectory(uint nBufferLength, StringBuilder lbBuffer);

    public static bool SetDirectory(string path)
    {
        if (SetDllDirectory(path)) return true;
        throw new Exception(string.Format("The call to SetDllDirectory failed. LastWin32Error = {0}", Marshal.GetLastWin32Error()));
    }

    public static string GetDirectory()
    {
        uint bufferLength = 260;
        var buffer = new StringBuilder((int)bufferLength);
        var result = GetDllDirectory(bufferLength, buffer);
        return result == 0 ? string.Empty : buffer.ToString();
    }
}
'@
    Add-Type -TypeDefinition $csharp
}

function Get-DllDirectory {
    <#
    .SYNOPSIS
    Retrieves the application-specific portion of the search path used to locate DLLs.

    .DESCRIPTION
    The Get-DllDirectory function retrieves the application-specific portion of
    the DLL search path that was previously set using Set-DllDirectory. This
    path is searched after the directory from which the application loaded, but
    before the system directory and other standard search locations.

    If no custom DLL directory has been set, or if the default search order has
    been restored, this function returns an empty string.

    .EXAMPLE
    Get-DllDirectory

    Returns the current application-specific DLL search path, or an empty string
    if none is set.

    .EXAMPLE
    Set-DllDirectory -Path "C:\MyLibs"
    $dllPath = Get-DllDirectory
    Write-Host "DLLs will be searched in: $dllPath"

    Sets a custom DLL directory and then retrieves it to confirm the setting.

    .OUTPUTS
    System.String
    Returns the application-specific DLL search path, or an empty string if no
    custom path is set or if the function fails.

    .NOTES
    See the Microsoft Win32 API documentation for GetDllDirectory below for more
    information.

    .LINK
    https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-getdlldirectorya

    #>
    [CmdletBinding()]
    [OutputType([string])]
    param()

    [DllDirectoryManager]::GetDirectory()
}

function Set-DllDirectory {
    <#
    .SYNOPSIS
    Adds the directory to the DLL search path for the current process.

    .DESCRIPTION
    The Set-DllDirectory function adds the specified directory to the search
    path used to locate DLLs for the current process. This is useful when
    working with native assemblies in PowerShell, as it allows you to load DLLs
    from a specific directory without having to change your current working
    directory.

    The function invokes the Windows SetDllDirectory API from kernel32.dll. When
    a directory is set using this function, the system searches for DLLs in the
    following order:

    1. The directory from which the application loaded
    2. The directory specified by the lpPathName parameter (this function)
    3. The system directory
    4. The 16-bit system directory
    5. The Windows directory
    6. The directories listed in the PATH environment variable

    .PARAMETER Path
    The path to the directory to add to the DLL search path. If a non-empty path
    is provided, it must exist and will be resolved to an absolute path. If an
    empty string is provided, the current directory is removed from the default
    DLL search order.

    .PARAMETER RestoreDefaults
    Restore the default DLL search order. This also restores safe DLL search
    mode based on the SafeDllSearchMode registry value.

    .EXAMPLE
    Set-DllDirectory -Path "C:\Program Files\MyApp\bin"

    Adds "C:\Program Files\MyApp\bin" to the DLL search path, allowing DLLs in
    that directory to be loaded without specifying the full path.

    .EXAMPLE
    Set-DllDirectory -Path .\lib
    Add-Type -Path .\lib\MyNativeWrapper.dll

    Adds the relative "lib" directory to the DLL search path, then loads a
    managed assembly that depends on native DLLs located in that same directory.

    .EXAMPLE
    Set-DllDirectory

    Removes the current directory from the default DLL search order.

    .EXAMPLE
    Set-DllDirectory -RestoreDefaults

    Restores the default DLL search order.

    .OUTPUTS
    System.Boolean
    Returns $true if the operation succeeded, or $false if it failed.

    .NOTES
    See the Microsoft Win32 API documentation for SetDllDirectory below for more
    information.

    .LINK
    https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-setdlldirectorya

    #>
    [CmdletBinding(DefaultParameterSetName = 'Path')]
    [OutputType([bool])]
    param (
        [Parameter(Position = 0, ParameterSetName = 'Path')]
        [AllowEmptyString()]
        [string]
        $Path,

        [Parameter(ParameterSetName = 'RestoreDefaults')]
        [switch]
        $RestoreDefaults
    )

    if ($Path.Length -gt 0) {
        $Path = (Resolve-Path $Path).Path
    }

    if ($RestoreDefaults) {
        [DllDirectoryManager]::SetDirectory($null)
    } else {
        [DllDirectoryManager]::SetDirectory($Path)
    }
}

addDllDirectoryManager

Export-ModuleMember -Function Get-DllDirectory, Set-DllDirectory