about_debuggers | Easy Powershell 2.0 Reference

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