Ideas for on your own in VB.NET

Generator DataMatrix in VB.NET Ideas for on your own

seen this technique, but you ll need to reverse it a bit and query the OS class first, then query the BIOS second). Query a list of hotfixes using WMI. (Hint: Microsoft formally refers to these as quick fix engineering). Is the list different from that returned by the Get-Hotfix cmdlet Display a list of services, including their current status, their start mode, and the account they use to log on. Can you find a class that will display a list of installed software products Do you consider the resulting list to be complete

Think about some of the things you might want to query from WMI, and see if you can find the classes and properties that expose that information. For example, you might want to find the service pack version of a computer: a service pack modifies the operating system, so you might start your search in a class that has something to do with the operating system (and you ve seen that class name in this chapter). Always try piping the object to Gm or Format-List * to see a full set of properties, or use a WMI explorer tool to review the full set of class properties.

Everyone s always telling you to multitask, right Why shouldn t PowerShell help you out with that by doing more than one thing at a time It turns out that PowerShell can do exactly that, especially for longer-running tasks that might involve multiple target computers. Make sure you ve read chapters 10 and 11 before you dive into this chapter, because we re going to take those remoting and WMI concepts a bit further.

You should think of PowerShell as a single-threaded application, meaning that it can only do one thing at once. You type a command, you hit Return, and the shell waits while that command executes. You can t start running a second command until the first finishes. With its background jobs functionality, however, PowerShell has the ability to move a command onto a separate background thread (actually a separate, background PowerShell process). That enables the command to run in the background, while you continue using the shell for something else. You have to make that decision before running the command; after you press Return, you can t decide to move a long-running command into the background. After commands are in the background, PowerShell provides mechanisms to check on their status, retrieve any results, and so forth.

Let s get a few bits of terminology out of the way first. PowerShell runs normal commands synchronously, meaning you hit Return and then wait for the command to

complete. Moving a job into the background allows it to run asynchronously, meaning that you can continue using the shell for other tasks while the command completes. There are a few important differences between running commands in these two ways:

When you run a command synchronously, you can respond to input requests. When running commands in the background, there s no opportunity to see input requests in fact, they ll stop the command from running. Synchronous commands produce error messages when something goes wrong. Background commands produce errors, but you won t see them immediately. You ll have to make arrangements to capture them, if necessary. ( 22 discusses that.) If you omit a required parameter on a synchronous command, PowerShell can prompt you for the missing information. On a background command, it can t, so the command will simply fail. The results of a synchronous command start displaying as soon as results become available. With a background command, you wait until the command finishes running and then retrieve the cached results.

I typically run commands synchronously to test them out and get them working properly, and only run them in the background after I know they re fully debugged and working as I expect them to. That way, I can ensure that the commands will run without problems, and that they will have the best chance of completing in the background. PowerShell refers to background commands as jobs, and there are several ways to create jobs, along with several commands to manage them.