TOPIC
    about_Debuggers

SHORT DESCRIPTION
    Describes the Windows PowerShell debugger.


LONG DESCRIPTION
    Debugging is the process of examining a script while it is running in
    order 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.
  

    Note: The Windows PowerShell debugger does not run remotely. To debug
          a script on a remote computer, copy the script to the local
          computer.


    You can use the features of the Windows PowerShell debugger to examine a 
    Windows PowerShell script, function, command, 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.
 

    Windows PowerShell offers several methods that you can use to debug 
    scripts, functions, and commands.


    Method 1: The Set-PsDebug cmdlet offers basic script debugging features,
              including stepping and tracing. For more information, type:
              "get-help set-psdebug".


    Method 2: 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.


    Method 3: 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.          


    Method 4: Use the Windows PowerShell debugger to debug a script. Or, use
              the debugger to debug a function or script block that you typed
              at the command prompt. You can set breakpoints, step through the
              script, examine the values of variables, run diagnostics and
              logging commands, and display 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.
    

      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).


      While in the debugger, you can also enter commands, display the value of
      variables, use cmdlets, and run scripts.


      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. 


  The Debugger Environment
      When you reach a breakpoint, you enter the debugger environment. The
      command prompt changes so that it begins with "[DBG]:". 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 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
      You cannot run the Windows PowerShell debugger in a remote session. To 
      debug a script on a remote computer, copy the script to the local 
      computer.


      The following command copies the Test.ps1 script from the Server01 remote
      computer to the local computer: 


          invoke-command -computername Server01 `
          {get-content c:\ps-test\test.ps1} | set-location c:\ps-test\test.ps1


  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


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