about_debuggers - PowerShell command help and examples

Describes the Windows PowerShell debugger. (about_debuggers)

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 C:\Windows>powershell get-help about_do -full

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