Functional differences between $PSScriptRoot and $MyInvocation

Question

Problem

I am working with Jenkins to deploy PowerShell scripts remotely. As such, I am trying to figure out if there will be problems utilizing $PSScriptRoot over $MyInvocation.MyCommand.Path for getting the current scripts root directory.

Details

A colleague in passing told me that utilizing $PSScriptRoot would be a bad idea for remote functionality as I might occasionally find that it does not return the expected value at runtime for one reason or another, even if it worked previously. However, could not explain why that would be.

In my research, I have not found anything on this that could explain this further or what the best practice way for avoiding such a problem would be. I primarily found that these two are basically interchangeable; however, $PSScriptRoot can only be used in PowerShell v3 or later. And through the help of several of you already, I have also come to learn that $MyInvocation has situational differences that allows it to change based on scope and module. But I still haven't found out if or why this would be a problem with PowerShell Remoting.

Example 001
So I have a PowerShell script in Jenkins, that uses $PSScriptRoot to act as the means of finding a script I wish to call via a relative path. Would I be able to rely on this to always provide the same/expected path to said script?

Example 002
Using a PowerShell script that was called by a PowerShell script that Jenkins initiated, would I be able to expect $PSScriptRoot to be able to provide me with the path of where that script actually sits, or would it give me a path based on Jenkins?

Personally, I am expecting both to be that $PSScriptRoot will provide me with the actual physical location of the script that is running rather than a relative path that changes based on the initial script that called it.

Since having this understanding would help save me a lot of time and headache, I am hoping that fellow programmers such as yourself could help enlighten me to IF this is true, and why such a problem would happen.

The Question

I am trying to find out if using $PSScriptRoot would cause me problems in PowerShell Remoting that would make using $MyInvocation a more viable option?

Answer 1

$PSScriptRoot.GetType().FullName
> System.String
$PSScriptRoot
> C:\Temp

$PSScriptRoot is an automatic variable which only holds a string object of the current script's directory.

$MyInvocation.GetType().FullName
> System.Management.Automation.InvocationInfo
$MyInvocation
> MyCommand             : test.ps1
> BoundParameters       : {}
> UnboundArguments      : {}
> ScriptLineNumber      : 0
> OffsetInLine          : 0
> HistoryId             : 4
> ScriptName            : 
> Line                  : 
> PositionMessage       : 
> PSScriptRoot          : 
> PSCommandPath         : 
> InvocationName        : C:\Temp\test.ps1
> PipelineLength        : 2
> PipelinePosition      : 1
> ExpectingInput        : False
> CommandOrigin         : Internal
> DisplayScriptPosition : 

$MyInvocation | Get-Member -Force
   TypeName: System.Management.Automation.InvocationInfo

Name                      MemberType   Definition                                                             
----                      ----------   ----------                                                             
pstypenames               CodeProperty System.Collections.ObjectModel.Collection`1[[System.String, mscorlib...
psadapted                 MemberSet    psadapted {MyCommand, BoundParameters, UnboundArguments, ScriptLineN...
psbase                    MemberSet    psbase {MyCommand, BoundParameters, UnboundArguments, ScriptLineNumb...
psextended                MemberSet    psextended {}                                                          
psobject                  MemberSet    psobject {BaseObject, Members, Properties, Methods, ImmediateBaseObj...
Equals                    Method       bool Equals(System.Object obj)                                         
GetHashCode               Method       int GetHashCode()                                                      
GetType                   Method       type GetType()                                                         
get_BoundParameters       Method       System.Collections.Generic.Dictionary[string,System.Object] get_Boun...
get_CommandOrigin         Method       System.Management.Automation.CommandOrigin get_CommandOrigin()         
get_DisplayScriptPosition Method       System.Management.Automation.Language.IScriptExtent get_DisplayScrip...
get_ExpectingInput        Method       bool get_ExpectingInput()                                              
get_HistoryId             Method       long get_HistoryId()                                                   
get_InvocationName        Method       string get_InvocationName()                                            
get_Line                  Method       string get_Line()                                                      
get_MyCommand             Method       System.Management.Automation.CommandInfo get_MyCommand()               
get_OffsetInLine          Method       int get_OffsetInLine()                                                 
get_PipelineLength        Method       int get_PipelineLength()                                               
get_PipelinePosition      Method       int get_PipelinePosition()                                             
get_PositionMessage       Method       string get_PositionMessage()                                           
get_PSCommandPath         Method       string get_PSCommandPath()                                             
get_PSScriptRoot          Method       string get_PSScriptRoot()                                              
get_ScriptLineNumber      Method       int get_ScriptLineNumber()                                             
get_ScriptName            Method       string get_ScriptName()                                                
get_UnboundArguments      Method       System.Collections.Generic.List[System.Object] get_UnboundArguments()  
set_DisplayScriptPosition Method       void set_DisplayScriptPosition(System.Management.Automation.Language...
ToString                  Method       string ToString()                                                      
BoundParameters           Property     System.Collections.Generic.Dictionary[string,System.Object] BoundPar...
CommandOrigin             Property     System.Management.Automation.CommandOrigin CommandOrigin {get;}        
DisplayScriptPosition     Property     System.Management.Automation.Language.IScriptExtent DisplayScriptPos...
ExpectingInput            Property     bool ExpectingInput {get;}                                             
HistoryId                 Property     long HistoryId {get;}                                                  
InvocationName            Property     string InvocationName {get;}                                           
Line                      Property     string Line {get;}                                                     
MyCommand                 Property     System.Management.Automation.CommandInfo MyCommand {get;}              
OffsetInLine              Property     int OffsetInLine {get;}                                                
PipelineLength            Property     int PipelineLength {get;}                                              
PipelinePosition          Property     int PipelinePosition {get;}                                            
PositionMessage           Property     string PositionMessage {get;}                                          
PSCommandPath             Property     string PSCommandPath {get;}                                            
PSScriptRoot              Property     string PSScriptRoot {get;}                                             
ScriptLineNumber          Property     int ScriptLineNumber {get;}                                            
ScriptName                Property     string ScriptName {get;}                                               
UnboundArguments          Property     System.Collections.Generic.List[System.Object] UnboundArguments {get;} 

Function Example { $MyInvocation } Example

MyCommand             : Example
BoundParameters       : {}
UnboundArguments      : {}
ScriptLineNumber      : 8
OffsetInLine          : 1
HistoryId             : 6
ScriptName            : C:\Temp\test.ps1
Line                  : Example
PositionMessage       : At C:\Temp\test.ps1:8 char:1
                        + Example
                        + ~~~~~~~
PSScriptRoot          : C:\Temp
PSCommandPath         : C:\Temp\test.ps1
InvocationName        : Example
PipelineLength        : 1
PipelinePosition      : 1
ExpectingInput        : False
CommandOrigin         : Internal
DisplayScriptPosition : 

$MyInvocation is an automatic variable with a very different type, generated for each scope. Its members and utility varies based on scope.

Tests completed on PSv5.1, Windows 7 SP1

Answer 2

Remember that both of these variables refer to the file that is being executed. If there is no file, they are empty.

In remoting, like when you use Invoke-Command -ScriptBlock { } there is no file.

It might work if you are calling a function that's in a module in the remoting session, and that function uses $PSScriptRoot or $MyInvocaton... in which case it would likely return whatever file it's in.

In the case of something like Jenkins, that's not remoting. Jenkins creates a temporary file and runs your code out of it, so that's the file that will be returned.