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about_Debuggers

Updated: May 8, 2014

Applies To: Windows PowerShell 2.0, Windows PowerShell 3.0, Windows PowerShell 4.0

TOPIC
    about_Debuggers

SHORT DESCRIPTION
    Describes the Windows PowerShell debugger.


LONG DESCRIPTION
    Debugging is the process of examining a script while it is running to
    identify and correct errors in the script instructions. The
    Windows PowerShell debugger is designed to help you examine and identify
    errors and inefficiencies in your scripts, functions, commands, Windows
    PowerShell workflows, or expressions.
  
    In Windows PowerShell 4.0, the Windows PowerShell debugger has been updated
    to debug scripts, functions, workflows, commands, or expressions that are
    running in the Windows PowerShell console (not ISE) on remote computers.
    You can run Enter-PSSession to start an interactive remote PowerShell session
    in which you can set breakpoints and debug script files and commands on the
    remote computer. Enter-PSSession functionality has been updated to let you
    reconnect to and enter a disconnected session that is running a script or
    command on a remote computer. If the running script hits a breakpoint,
    your client session automatically starts the debugger. If the disconnected
    session that is running a script has already hit a breakpoint, and is stopped
    at the breakpoint, Enter-PSSession automatically starts the command-line
    debugger, after you reconnect to the session.

    The Windows PowerShell 4.0 debugger can also be used to debug Windows
    PowerShell workflows, in either the Windows PowerShell console, or in 
    Windows PowerShell ISE.

    You can use the features of the Windows PowerShell debugger to examine a
    Windows PowerShell script, function, command, workflow, or expression
    while it is running. The Windows PowerShell debugger includes a set of
    cmdlets that let you set breakpoints, manage breakpoints, and view the call
    stack.

    
  Debugger Cmdlets
      The Windows PowerShell debugger includes the following set of cmdlets:


          Set-PsBreakpoint:     Sets breakpoints on lines, variables, and
                                commands. 

          Get-PsBreakpoint:     Gets breakpoints in the current session.

          Disable-PsBreakpoint: Turns off breakpoints in the current session.

          Enable-PsBreakpoint:  Re-enables breakpoints in the current session.

          Remove-PsBreakpoint:  Deletes breakpoints from the current session.

          Get-PsCallStack:      Displays the current call stack. 


  Starting and Stopping the Debugger
      To start the debugger, set one or more breakpoints. Then, run the script,
      command, or function that you want to debug. 


      When you reach a breakpoint, execution stops, and control is turned over 
      to the debugger.


      To stop the debugger, run the script, command, or function until it is 
      complete. Or, type "stop" or "t".
  

  Debugger Commands
      When you use the debugger in the Windows PowerShell console, use the 
      following commands to control the execution. In Windows PowerShell ISE,
      use commands on the Debug menu.

      Note: For information about how to use the debugger in other host
          applications, see the host application documentation.


 s, Step-into        Executes the next statement and then stops.


 v, Step-over        Executes the next statement, but skips functions
                            and invocations. The skipped statements are
                            executed, but not stepped through.


 o, Step-out         Steps out of the current function; up one level
                            if nested. If in the main body, it continues to
                            the end or the next breakpoint. The skipped
                            statements are executed, but not stepped through.


 c, Continue         Continues to run until the script is complete or
                            until the next breakpoint is reached. The skipped
                            statements are executed, but not stepped through.


        l, List             Displays the part of the script that is executing.
                            By default, it displays the current line, five
                            previous lines, and 10 subsequent lines. To continue
                            listing the script, press ENTER.
                        

        l <m>, List         Displays 16 lines of the script beginning with the
                            line number specified by <m>.                           

        l <m> <n>, List     Displays <n> lines of the script, beginning with the
                            line number specified by <m>.                           

        q, Stop             Stops executing the script, and exits the debugger.


        k, Get-PsCallStack  Displays the current call stack.


<Enter>             Repeats the last command if it was Step (s), 
                            Step-over (v), or List (l). Otherwise, represents a
                            submit action.  
                           

?, h                Displays the debugger command Help.


      To exit the debugger, use Stop (q).

      By using these debugger commands, you can run a script, stop on a point
      of concern, examine the values of variables and the state of the system,
      and continue running the script until you have identified a problem. 

      NOTE:  If you step into a statement with a redirection operator, 
             such as ">", the Windows PowerShell debugger steps over all
             remaining statements in the script.


  
  Displaying the Values of script Variables
   
      While you are in the debugger, you can also enter commands, display the
      value of variables, use cmdlets, and run scripts at the command line.

      You can display the current value of all variables in the script that is
      being debugged, except for the following automatic variables: 
  
          $_
          $Args
          $Input
          $MyInvocation
          $PSBoundParameters

      If you try to display the value of any of these variables, you get the 
      value of that variable for in an internal pipeline the debugger uses, not
      the value of the variable in the script.

      To display the value these variables for the script that is being debugged,
      in the script, assign the value of the automatic variable to a new variable.
      Then you can display the value of the new variable.

      For example,

          $scriptArgs = $Args
          $scriptArgs

      In the example in this topic, the value of the $MyInvocation variable is
      reassigned as follows:

          $scriptname = $MyInvocation.MyCommand.Path
          

      
  The Debugger Environment
      When you reach a breakpoint, you enter the debugger environment. The
      command prompt changes so that it begins with "[DBG]:". If you are 
      debugging a workflow, the prompt is "[WFDBG]". You can customize
      the prompt.

     
      Also, in some host applications, such as the Windows PowerShell console,
      (but not in Windows PowerShell Integrated Scripting Environment [ISE]), 
      a nested prompt opens for debugging. You can detect the nested prompt by
      the repeating greater-than characters (ASCII 62) that appear at the
      command prompt.


      For example, the following is the default debugging prompt in the
      Windows PowerShell console:


          [DBG]: PS (get-location)>>>


      You can find the nesting level by using the $NestedPromptLevel 
      automatic variable.


      Additionally, an automatic variable, $PSDebugContext, is defined in 
      the local scope. You can use the presence of the $PsDebugContext 
      variable to determine whether you are in the debugger.


      For example:

 
          if ($psdebugcontext) {"Debugging"} else {"Not Debugging"}


      You can use the value of the $PSDebugContext variable in your
      debugging.


[DBG]: PS>>> $psdebugcontext.invocationinfo

        Name   CommandLineParameters  UnboundArguments  Location
        ----   ---------------------  ----------------  --------
        =      {}                     {}                C:\ps-test\vote.ps1 (1)


  Debugging and Scope
      Breaking into the debugger does not change the scope in which
      you are operating, but when you reach a breakpoint in a script,
      you move into the script scope. The script scope is a child 
      of the scope in which you ran the debugger.


      To find the variables and aliases that are defined in the 
      script scope, use the Scope parameter of the Get-Alias or
      Get-Variable cmdlets.


      For example, the following command gets the variables in the
      local (script) scope:


  get-variable -scope 0


      You can abbreviate the command as:


gv -s 0


      This is a useful way to see only the variables that you defined in the
      script and that you defined while debugging.


  Debugging at the Command Line
      When you set a variable breakpoint or a command breakpoint, you can set
      the breakpoint only in a script file. However, by default, the breakpoint
      is set on anything that runs in the current session. 


      For example, if you set a breakpoint on the $name variable, the debugger
      breaks on any $name variable in any script, command, function, script 
      cmdlet or expression that you run until you disable or remove the 
      breakpoint.


      This allows you to debug your scripts in a more realistic context in 
      which they might be affected by functions, variables, and other scripts
      in the session and in the user's profile.


      Line breakpoints are specific to script files, so they are set only in
      script files.  


  Debugging Workflows
      The Windows PowerShell 4.0 debugger can be used to debug Windows
      PowerShell workflows, either in the Windows PowerShell console, or in
      Windows PowerShell ISE. There are some limitations with using
      the Windows PowerShell debugger to debug workflows.

      -- You can view workflow variables while you are in the debugger, but
         setting workflow variables from within the debugger is not supported.
      -- Tab completion when stopped in the workflow debugger is not
         available.
      -- Workflow debugging works only with synchronous running of workflows from
         a Windows PowerShell script. You cannot debug workflows if they are
         running as a job (with the –AsJob parameter).
      -- Other nested debugging scenarios--such as a workflow calling another
         workflow, or a workflow calling a script--are not implemented.

      The following example demonstrates debugging a workflow. Note that when
      the debugger steps into the workflow function, the debugger prompt changes
      to [WFDBG].

          PS C:\> Set-PSBreakpoint -Script C:\TestWFDemo1.ps1 -Line 8

          ID Script           Line Command    Variable     Action
          -- ------           ---- -------    --------     ------
          0 TestWFDemo1.ps1   8

          PS C:\> C:\TestWFDemo1.ps1
          Entering debug mode. Use h or ? for help.

          Hit Line breakpoint on 'C:\TestWFDemo1.ps1:8'

          At C:\TestWFDemo1.ps1:8 char:5
          +     Write-Output -InputObject "Now writing output:"
          +     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          [WFDBG:localhost]: PS C:\>> list

              3:
              4:  workflow SampleWorkflowTest
              5:  {
              6:      param ($MyOutput)
              7:
              8:*     Write-Output -InputObject "Now writing output:"
              9:      Write-Output -Input $MyOutput
             10:
             11:      Write-Output -InputObject "Get PowerShell process:"
             12:      Get-Process -Name powershell
             13:
             14:      Write-Output -InputObject "Workflow function complete."
             15:  }
             16:
             17:  # Call workflow function
             18:  SampleWorkflowTest -MyOutput "Hello"

          [WFDBG:localhost]: PS C:\>> $MyOutput
          Hello
          [WFDBG:localhost]: PS C:\>> stepOver
          Now writing output:
          At C:\TestWFDemo1.ps1:9 char:5
          +     Write-Output -Input $MyOutput
          +     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          [WFDBG:localhost]: PS C:\>> list

              4:  workflow SampleWorkflowTest
              5:  {
              6:      param ($MyOutput)
              7:
              8:      Write-Output -InputObject "Now writing output:"
              9:*     Write-Output -Input $MyOutput
             10:
             11:      Write-Output -InputObject "Get PowerShell process:"
             12:      Get-Process -Name powershell
             13:
             14:      Write-Output -InputObject "Workflow function complete."
             15:  }
             16:
             17:  # Call workflow function
             18:  SampleWorkflowTest -MyOutput "Hello"
             19:

          [WFDBG:localhost]: PS C:\>> stepOver
          Hello
          At C:\TestWFDemo1.ps1:11 char:5
          +     Write-Output -InputObject "Get PowerShell process:"
          +     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          [WFDBG:localhost]: PS C:\>> stepOut
          Get PowerShell process:

          Handles  NPM(K)    PM(K)   WS(K) VM(M)   CPU(s)     Id ProcessName    PSComputerName
          -------  ------    -----   ----- -----   ------     -- -----------    --------------
              433      35   106688   128392   726     2.67   7124 powershell    localhost
              499      44   134244   172096   787     2.79   7452 powershell    localhost
          Workflow function complete.


  Debugging Functions
      When you set a breakpoint on a function that has Begin, Process, and
      End sections, the debugger breaks at the first line of each section.


      For example:


              function test-cmdlet
              {
                  begin
                  {
                      write-output "Begin"
                  }
                  process
                  {
                      write-output "Process"
                  }
                  end
                  {
                      write-output "End"
                  }
              }
        
          C:\PS> set-psbreakpoint -command test-cmdlet

          C:\PS> test-cmdlet
    
          Begin
          Entering debug mode. Use h or ? for help.

          Hit Command breakpoint on 'prompt:test-cmdlet'

          test-cmdlet

          [DBG]: C:\PS> c
          Process
          Entering debug mode. Use h or ? for help.

          Hit Command breakpoint on 'prompt:test-cmdlet'

          test-cmdlet

          [DBG]: C:\PS> c
          End
          Entering debug mode. Use h or ? for help.

          Hit Command breakpoint on 'prompt:test-cmdlet'

          test-cmdlet

          [DBG]: C:\PS> 


  Debugging Remote Scripts
      In Windows PowerShell 4.0, you can run the Windows PowerShell debugger in
      a remote session, in the Windows PowerShell 4.0 console. Enter-PSSession
      functionality has been updated to let you reconnect to and enter a disconnected
      session that is running on a remote computer, and currently running a script.
      If the running script hits a breakpoint, your client session automatically
      starts the debugger. The following is an example that shows how this works,
      with breakpoints set in a script at lines 6, 11, 22, and 25. Note that in the
      example, when the debugger starts, there are two identifying prompts: the
      name of the computer on which the session is running, and the DBG prompt that
      lets you know you are in debugging mode.
      
          Enter-Pssession -Cn localhost
          [localhost]: PS C:\psscripts> Set-PSBreakpoint .\ttest19.ps1 6,11,22,25

          ID Script          Line     Command          Variable          Action
          -- ------          ----     -------          --------          ------
          0 ttest19.ps1          6
          1 ttest19.ps1          11
          2 ttest19.ps1          22
          3 ttest19.ps1          25

           [localhost]: PS C:\psscripts> .\ttest19.ps1
          Hit Line breakpoint on 'C:\psscripts\ttest19.ps1:11'

          At C:\psscripts\ttest19.ps1:11 char:1
          + $winRMName = "WinRM"
          + ~
           [localhost]: [DBG]: PS C:\psscripts>> list


          6:      1..5 | foreach { sleep 1; Write-Output "hello2day $_" }
          7:  }
          8:
          9:  $count = 10
          10:  $psName = "PowerShell"
          11:* $winRMName = "WinRM"
          12:  $myVar = 102
          13:
          14:  for ($i=0; $i -lt $count; $i++)
          15:  {
          16:      sleep 1
          17:      Write-Output "Loop iteration is: $i"
          18:      Write-Output "MyVar is $myVar"
          19:
          20:      hello2day
          21:

           [localhost]: [DBG]: PS C:\psscripts>> stepover
          At C:\psscripts\ttest19.ps1:12 char:1
          + $myVar = 102
          + ~
           [localhost]: [DBG]: PS C:\psscripts>> quit
           [localhost]: PS C:\psscripts> Exit-PSSession
          PS C:\psscripts>


  Examples
      This test script detects the version of the operating system and 
      displays a system-appropriate message. It includes a function, a function
      call, and a variable. 


      The following command displays the contents of the test script file:


  c:>\PS-test>  get-content test.ps1


  function psversion {
             "Windows PowerShell " + $psversiontable.psversion
              if ($psversiontable.psversion.major -lt 2) {
                  "Upgrade to Windows PowerShell 2.0!"
              }
              else {
                  "Have you run a background job today (start-job)?"
              }
          }

  $scriptname = $MyInvocation.MyCommand.Path
  psversion
  "Done $scriptname."


      To start, set a breakpoint at a point of interest in the script, such
      as a line, command, variable, or function.
 

      Start by creating a line breakpoint on the first line of the Test.ps1
      script in the current directory.


          PS C:\ps-test> set-psbreakpoint -line 1 -script test.ps1 


      You can abbreviate this command as:


          PS C:\ps-test> spb 1 -s test.ps1

        
      The command returns a line-breakpoint object
      (System.Management.Automation.LineBreakpoint).


      Column     : 0
            Line       : 1
            Action     :
            Enabled    : True
            HitCount   : 0
            Id         : 0
            Script     : C:\ps-test\test.ps1
            ScriptName : C:\ps-test\test.ps1


      Now, start the script.


  PS C:\ps-test> .\test.ps1


      When the script reaches the first breakpoint, the breakpoint message
      indicates that the debugger is active. It describes the breakpoint and 
      previews the first line of the script, which is a function declaration. 
      The command prompt also changes to indicate that the debugger has 
      control.


      The preview line includes the script name and the line number of the
      previewed command.


          Entering debug mode. Use h or ? for help.

          Hit Line breakpoint on 'C:\ps-test\test.ps1:1'

          test.ps1:1   function psversion {
          DBG>


      Use the Step command (s) to execute the first statement in the script
      and to preview the next statement. The next statement uses the 
      $MyInvocation automatic variable to set the value of the $ScriptName 
      variable to the path and file name of the script file.


          DBG> s
          test.ps1:11  $scriptname = $MyInvocation.MyCommand.Path


      At this point, the $ScriptName variable is not populated, but you can
      verify the value of the variable by displaying its value. In this case,
      the value is $null.


          DBG> $scriptname
          DBG>

    
      Use another Step command (s) to execute the current statement and to 
      preview the next statement in the script. The next statement calls the 
      PsVersion function.


  DBG> s
  test.ps1:12  psversion


      At this point, the $ScriptName variable is populated, but you verify the
      value of the variable by displaying its value. In this case, the value
      is set to the script path.


          DBG> $scriptname
          C:\ps-test\test.ps1
   

      Use another Step command to execute the function call. Press ENTER,
      or type "s" for Step.


  DBG> s
  test.ps1:2       "Windows PowerShell " + $psversiontable.psversion


      The debug message includes a preview of the statement in the function.
      To execute this statement and to preview the next statement in the 
      function, you can use a Step command. But, in this case, use a Step-Out 
      command (o). It completes the execution of the function (unless it 
      reaches a breakpoint) and steps to the next statement in the script.


  DBG> o
  Windows PowerShell 2.0
  Have you run a background job today (start-job)?
  test.ps1:13  "Done $scriptname"


      Because we are on the last statement in the script, the Step, Step-Out, 
      and Continue commands have the same effect. In this case, use 
      Step-Out (o). 


  Done C:\ps-test\test.ps1
  PS C:\ps-test>


      The Step-Out command executes the last command. The standard command 
      prompt indicates that the debugger has exited and returned control to the
      command processor.


      Now, run the debugger again. First, to delete the current 
      breakpoint, use the Get-PsBreakpoint and Remove-PsBreakpoint cmdlets.
      (If you think you might reuse the breakpoint, use the 
      Disable-PsBreakpoint cmdlet instead of Remove-PsBreakpoint.)


  PS C:\ps-test> Get-PsBreakpoint | Remove-PSBreakpoint


      You can abbreviate this command as:


  PS C:\ps-test> gbp | rbp


      Or, run the command by writing a function, such as the following 
      function:


  function delbr { gbp | rbp }


      Now, create a breakpoint on the $scriptname variable. 


  PS C:\ps-test> set-psbreakpoint -variable scriptname -script test.ps1


      You can abbreviate the command as: 


  PS C:\ps-test> sbp -v scriptname -s test.ps1


      Now, start the script. The script reaches the variable breakpoint. The 
      default mode is Write, so execution stops just before the statement
      that changes the value of the variable.


  PS C:\ps-test> .\test.ps1
  Hit Variable breakpoint on 'C:\ps-test\test.ps1:$scriptname'
          (Write access)

  test.ps1:11  $scriptname = $MyInvocation.mycommand.path
  DBG>


      Display the current value of the $scriptname variable, which
      is $null.


          DBG> $scriptname
          DBG>

      Use a Step command (s) to execute the statement that populates
      the variable. Then, display the new value of the $scriptname
      variable.


  DBG> $scriptname
  C:\ps-test\test.ps1


      Use a Step command (s) to preview the next statement in the script.


  DBG> s
  test.ps1:12  psversion

   
      The next statement is a call to the PsVersion function. To skip the
      function but still execute it, use a Step-Over command (v). If you are
      already in the function when you use Step-Over, it is not effective. The 
      function call is displayed, but it is not executed.


  DBG> v
  Windows PowerShell 2.0
  Have you run a background job today (start-job)?
  test.ps1:13  "Done $scriptname"   


      The Step-Over command executes the function, and it previews the next
      statement in the script, which prints the final line.


      Use a Stop command (t) to exit the debugger. The command prompt 
      reverts to the standard command prompt.


  C:\ps-test>


      To delete the breakpoints, use the Get-PsBreakpoint and
      Remove-PsBreakpoint cmdlets.


  PS C:\ps-test> Get-PsBreakpoint | Remove-PSBreakpoint


      Create a new command breakpoint on the PsVersion function.


          PS C:\ps-test> Set-PsBreakpoint -command psversion -script test.ps1 


      You can abbreviate this command to:


          PS C:\ps-test> sbp -c psversion -s test.ps1 


      Now, run the script.


          PS C:\ps-test> .\test.ps1
          Hit Command breakpoint on 'C:\ps-test\test.ps1:psversion'

          test.ps1:12  psversion
          DBG>


      The script reaches the breakpoint at the function call. At this point, 
      the function has not yet been called. This gives you the opportunity
      to use the Action parameter of Set-PsBreakpoint to set conditions for
      the execution of the breakpoint or to perform preparatory or diagnostic
      tasks, such as starting a log or invoking a diagnostic or security
      script.


      To set an action, use a Continue command (c) to exit the script, and a
      Remove-PsBreakpoint command to delete the current breakpoint. 
      (Breakpoints are read-only, so you cannot add an action to the current
      breakpoint.)


  DBG> c
  Windows PowerShell 2.0
  Have you run a background job today (start-job)?
  Done C:\ps-test\test.ps1

  PS C:\ps-test> get-psbreakpoint | remove-psbreakpoint
  PS C:\ps-test>


      Now, create a new command breakpoint with an action. The following
      command sets a command breakpoint with an action that logs the value
      of the $scriptname variable when the function is called. Because the
      Break keyword is not used in the action, execution does not stop. (The
      backtick (`) is the line-continuation character.)


         PS C:\ps-test> set-psbreakpoint -command psversion -script test.ps1  `
         -action { add-content "The value of `$scriptname is $scriptname." `
         -path action.log}


      You can also add actions that set conditions for the breakpoint. In
      the following command, the command breakpoint is executed only if the
      execution policy is set to RemoteSigned, the most restrictive policy
      that still permits you to run scripts. (The backtick (`) is the
      continuation character.)   


          PS C:\ps-test> set-psbreakpoint -script test.ps1 -command psversion `
          -action { if ((get-executionpolicy) -eq "RemoteSigned") { break }}


      The Break keyword in the action directs the debugger to execute the
      breakpoint. You can also use the Continue keyword to direct the debugger
      to execute without breaking. Because the default keyword is Continue, 
      you must specify Break to stop execution.


      Now, run the script.


  PS C:\ps-test> .\test.ps1
  Hit Command breakpoint on 'C:\ps-test\test.ps1:psversion'

  test.ps1:12  psversion

    
      Because the execution policy is set to RemoteSigned, execution stops
      at the function call. 


      At this point, you might want to check the call stack. Use the
      Get-PsCallStack cmdlet or the Get-PsCallStack debugger command (k).
      The following command gets the current call stack.


  DBG> k
  2: prompt
  1: .\test.ps1: $args=[]
  0: prompt: $args=[]


      This example demonstrates just a few of the many ways to use the Windows
      PowerShell debugger. 


      For more information about the debugger cmdlets, type the following
      command:


          help <cmdlet-name> -full


      For example, type:


          help set-psbreakpoint -full


  Other Debugging Features in Windows PowerShell

    In addition to the Windows PowerShell debugger, Windows PowerShell includes
    several other features that you can use to debug scripts and functions.

     
    -- Windows PowerShell Integrated Scripting Environment (ISE) includes
       an interactive graphical debugger. For more information, start Windows
       PowerShell ISE and press F1.

    -- The Set-PSDebug cmdlet offers very basic script debugging features,
       including stepping and tracing. 

    -- Use the Set-StrictMode cmdlet to detect references to 
       uninitialized variables, to references to non-existent properties
       of an object, and to function syntax that is not valid. 

    -- Add diagnostic statements to a script, such as statements that
       display the value of variables, statements that read input from
       the command line, or statements that report the current 
       instruction. Use the cmdlets that contain the Write verb for 
       this task, such as Write-Host, Write-Debug, Write-Warning, and
       Write-Verbose.          


SEE ALSO
    Disable-PsBreakpoint
    Enable-PsBreakpoint
    Get-PsBreakpoint   
    Get-PsCallStack
    Remove-PsBreakpoint
    Set-PsBreakpoint 
    Set-PsDebug
    Set-Strictmode
    Write-Debug
    Write-Verbose    



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