Common points of confusion in Visual Basic .NET

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Common points of confusion
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demo.ps1:4 write-debug "`$name contains $name" [DBG]: PS C:\>>> $name server-r2 [DBG]: PS C:\>>> test-connection $name -quiet True [DBG]: PS C:\>>>
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This gives me the chance to test commands, see what s inside variables or properties, and so forth, without having to add a lot of Write-Debug commands. You ll notice, in fact, that the shell generates its own debug output automatically as part of the breakpoint process, and that it automatically turns the Debug pipeline on for the duration of the script s execution. When I m done debugging, I can remove the breakpoints:
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PS C:\> Get-PSBreakpoint | Remove-PSBreakpoint
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And I can go back to executing my script normally. Working this way takes a bit of getting used to, but it s a very effective debugging tool once you do so. Breakpoints are also supported within the PowerShell ISE. To set a line breakpoint, move your cursor to the desired line and press F9. You can still set command and variable breakpoints, but you have to run Set-PSBreakpoint from the command pane there s no function key or graphical shortcut. The ISE will visually indicate where line breakpoints occur, using a red highlight. If you run the script within the ISE, breakpoint lines will be highlighted in yellow when the script reaches one of those lines. At that time, you can hover your cursor over any variable to see a tooltip with the contents of that variable. It s a vaguely similar experience to working in a fullfledged development environment like Visual Studio, albeit with much more simplistic functionality.
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23.5 Common points of confusion
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The biggest single mistake I see students make when it comes to debugging is something I call shotgun debugging. It means they see an error, they panic, and they start changing everything they can, without taking the time to verify what was wrong. Take my original example in listing 23.1: I ve used that same example in dozens of classes, and as you know, that example is purposely buggy. When I ask the class to try to fix it, there s almost always one student who spends half an hour checking network connectivity, logging off and logging back on, rebooting the remote computer, and so on, assuming all the while that the script must be fine, and that the problem lies in the infrastructure somewhere. Don t get caught in that trap. When a script or command isn t working the way you think it should, say three things to yourself:
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I need to figure out exactly what I think each line of this script is supposed to do. I need to assume that every command is incorrect, and read the help to verify each parameter. I should run each command individually in a test environment to make sure it works the way the script thinks it works.
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Debugging techniques
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I need to examine property and variable contents to make sure they contain what I think they contain.
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If you can discipline yourself to slowing down, taking a deep breath, and debugging in a calm, methodical fashion that focuses on expectations versus reality, you ll never meet a script you can t debug.
23.6 Lab
Listing 23.3 is a script that includes a function. At the end of the script (on line 14) is a command that actually runs the function. The goal is to get a table that includes each computer s name, its Windows build number, and its BIOS serial number. The script definitely has bugs in it both syntax and logic. Fix them.
Listing 23.3 23 lab script
function Get-Inventory { PROCESS { $computername = $_ $os = Get-WmiObject Win32_OperatingSystem -comp $computername $bios = Get-WmiObject Win32_BIOS -comp $computername $ojb = New-Object PSObject $obj | Add-Membrr NoteProperty ComputerName $computername $obj | Add-Member NoteProperty OSBuild ($os.buildnumber) $obj | Add-Member NoteProperty BIOSSerial ($bios.serialno) Write-Output $ojb } } localhost,server-r2 | get-inventory
Remember that one of my suggested best practices is for you to always spell out full cmdlet and parameter names in a script, and that includes scripts given to you by other people. That would be a good place to start with this one: correcting the names. In the case of the Add-Member cmdlet, this script doesn t even include parameter names they re all positional. You should consider correcting that, too, by adding in the appropriate parameter names. Use the help files to guide you. As a tip, SAPIEN PrimalScript includes a feature on its edit menu that will convert aliases to their full cmdlet names. You may be able to find a free plug-in for PowerGUI that does something similar, and perhaps also expands the parameter names. If you use a different editor (other than the PowerShell ISE), ask the vendor to supply a cmdlet and parameter name expansion feature in a future version.
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