What's the best way to determine the location of the current PowerShell script?

PowerShell 3+

# This is an automatic variable set to the current file's/module's directory
$PSScriptRoot

PowerShell 2

Prior to PowerShell 3, there was not a better way than querying the MyInvocation.MyCommand.Definition property for general scripts. I had the following line at the top of essentially every PowerShell script I had:

$scriptPath = split-path -parent $MyInvocation.MyCommand.Definition

If you are creating a V2 Module, you can use an automatic variable called $PSScriptRoot.

From PS > Help automatic_variable

$PSScriptRoot
       Contains the directory from which the script module is being executed.
       This variable allows scripts to use the module path to access other
       resources.

For PowerShell 3.0

$PSCommandPath
    Contains the full path and file name of the script that is being run. 
    This variable is valid in all scripts.

The function is then:

function Get-ScriptDirectory {
    Split-Path -Parent $PSCommandPath
}

For PowerShell 3+

function Get-ScriptDirectory {
    if ($psise) {
        Split-Path $psise.CurrentFile.FullPath
    }
    else {
        $global:PSScriptRoot
    }
}

I've placed this function in my profile. It works in ISE using F8/Run Selection too.

Maybe I'm missing something here... but if you want the present working directory you can just use this: (Get-Location).Path for a string, or Get-Location for an object.

Unless you're referring to something like this, which I understand after reading the question again.

function Get-Script-Directory
{
    $scriptInvocation = (Get-Variable MyInvocation -Scope 1).Value
    return Split-Path $scriptInvocation.MyCommand.Path
}

I use the automatic variable $ExecutionContext. It will work from PowerShell 2 and later.

 $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath('.\')

$ExecutionContext Contains an EngineIntrinsics object that represents the execution context of the Windows PowerShell host. You can use this variable to find the execution objects that are available to cmdlets.

Very similar to already posted answers, but piping seems more PowerShell-like:

$PSCommandPath | Split-Path -Parent

It took me a while to develop something that took the accepted answer and turned it into a robust function.

I am not sure about others, but I work in an environment with machines on both PowerShell version 2 and 3, so I needed to handle both. The following function offers a graceful fallback:

Function Get-PSScriptRoot
{
    $ScriptRoot = ""

    Try
    {
        $ScriptRoot = Get-Variable -Name PSScriptRoot -ValueOnly -ErrorAction Stop
    }
    Catch
    {
        $ScriptRoot = Split-Path $script:MyInvocation.MyCommand.Path
    }

    Write-Output $ScriptRoot
}

It also means that the function refers to the Script scope rather than the parent's scope as outlined by Michael Sorens in one of his blog posts.

I needed to know the script name and where it is executing from.

Prefixing "$global:" to the MyInvocation structure returns the full path and script name when called from both the main script, and the main line of an imported .PSM1 library file. It also works from within a function in an imported library.

After much fiddling around, I settled on using $global:MyInvocation.InvocationName. It works reliably with CMD launch, Run With Powershell, and the ISE. Both local and UNC launches return the correct path.

I always use this little snippet which works for PowerShell and ISE the same way:

# Set active path to script-location:
$path = $MyInvocation.MyCommand.Path
if (!$path) {$path = $psISE.CurrentFile.Fullpath}
if ($path)  {$path = Split-Path $path -Parent}
Set-Location $path

Using pieces from all of these answers and the comments, I put this together for anyone who sees this question in the future. It covers all of the situations listed in the other answers, and I've added another one I found as a fail-safe.

function Get-ScriptPath()
{
    # If using PowerShell ISE
    if ($psISE)
    {
        $ScriptPath = Split-Path -Parent -Path $psISE.CurrentFile.FullPath
    }
    # If using PowerShell 3.0 or greater
    elseif($PSVersionTable.PSVersion.Major -gt 3)
    {
        $ScriptPath = $PSScriptRoot
    }
    # If using PowerShell 2.0 or lower
    else
    {
        $ScriptPath = split-path -parent $MyInvocation.MyCommand.Path
    }

    # If still not found
    # I found this can happen if running an exe created using PS2EXE module
    if(-not $ScriptPath) {
        $ScriptPath = [System.AppDomain]::CurrentDomain.BaseDirectory.TrimEnd('\')
    }

    # Return result
    return $ScriptPath
}

I found that the older solutions posted here didn't work for me on PowerShell V5. I came up with this:

try {
    $scriptPath = $PSScriptRoot
    if (!$scriptPath)
    {
        if ($psISE)
        {
            $scriptPath = Split-Path -Parent -Path $psISE.CurrentFile.FullPath
        }
        else {
            Write-Host -ForegroundColor Red "Cannot resolve script file's path"
            exit 1
        }
    }
}
catch {
    Write-Host -ForegroundColor Red "Caught Exception: $($Error[0].Exception.Message)"
    exit 2
}

Write-Host "Path: $scriptPath"

You might also consider split-path -parent $psISE.CurrentFile.Fullpath if any of the other methods fail. In particular, if you run a file to load a bunch of functions and then execute those functions with-in the ISE shell (or if you run-selected), it seems the Get-Script-Directory function as above doesn't work.

If you want to load modules from a path relative to where the script runs, such as from a "lib" subfolder", you need to use one of the following:

$PSScriptRoot which works when invoked as a script, such as via the PowerShell command $psISE.CurrentFile.FullPath which works when you're running inside ISE

But if you're in neither, and just typing away within a PowerShell shell, you can use:

pwd.Path

You can could assign one of the three to a variable called $base depending on the environment you're running under, like so:

$base=$(if ($psISE) {Split-Path -Path $psISE.CurrentFile.FullPath} else {$(if ($global:PSScriptRoot.Length -gt 0) {$global:PSScriptRoot} else {$global:pwd.Path})})

Then in your scripts, you can use it like so:

Import-Module $base\lib\someConstants.psm1
Import-Module $base\lib\myCoolPsModule1.psm1
#etc.

function func1() 
{
   $inv = (Get-Variable MyInvocation -Scope 1).Value
   #$inv.MyCommand | Format-List *   
   $Path1 = Split-Path $inv.scriptname
   Write-Host $Path1
}

function Main()
{
    func1
}

Main