Adding logic and loops in Visual Basic .NET

Drawer Data Matrix ECC200 in Visual Basic .NET Adding logic and loops

ForEach may seem familiar to you, because we ve used the ForEach-Object cmdlet (and perhaps you ve used that cmdlet s foreach alias) in previous chapters. The construct works much the same as the cmdlet: both go through a collection of objects one at a time. With the construct, you get to define the variable that contains one object at a time (I used $service in the preceding example); with the cmdlet, PowerShell forces you to use the $_ placeholder. For example, I could rewrite the previous example like this:

Get-Service | ForEach-Object { Write-Host $_.Name }

When you use the construct, you use the in keyword, as I did in my ForEach example. When you use the cmdlet, you don t need to use the in keyword because PowerShell automatically enumerates into the built-in $_ placeholder.

ForEach is an excellent example of why scripting like this isn t always necessary in Pow-

erShell, even though PowerShell will let you do it. That previous example could have been accomplished more easily in the pipeline:

That will produce new objects that have only a Name property. If you wanted to get the actual names as simple string values, you could do this:

Both of those options involve a lot less typing. The point here is that using ForEach is often (but not always) an indicator that you re taking a scripting approach rather than a pure PowerShell approach. You won t get in trouble for taking a scripting approach, but it often requires a lot more typing and a script than using a couple of commands. There are only two times when I find myself legitimately using ForEach:

When there s no cmdlet capable of doing what I need to a bunch of objects at once. This most often happens when I need to execute a method against a bunch of objects, and there isn t a cmdlet that can perform the equivalent task. When I need to manually unwind a bunch of objects and send them off, one at a time, to a custom function that I ve written, which can only work with one at a time. You ll see an example of this in the next chapter.

If you have some scripting or programming in your background, and you want to try to force yourself to take a more pure PowerShell approach, use ForEach as a cue. When you find yourself using it, see if there isn t an easier way. For example, instead of this,

$processes = Get-Process ForEach ($process in $processes) { If ($process.name -eq 'notepad') { $process.kill() } }

you could just do this,

or better yet, this,

or best of all, this:

These all accomplish the same thing, but the command-oriented way takes a lot less typing (and to me, is easier to read and figure out) than the scripting-oriented way.

For this lab, you ll probably want to work within the PowerShell ISE. That will make it easier to enter multiline scripts and commands, and it ll make it easier to edit if you make any mistakes or want to make a change.

Create a script that uses Read-Host to prompt for a remote computer name. If the computer name is localhost, then don t do anything. Otherwise, query the Win32_OperatingSystem WMI class from the specified computer. Create a script that queries the Win32_LogicalDisk WMI class from the local computer. Use a ForEach loop to enumerate the instances returned by the query. Within the ForEach loop, display the DeviceID property. Then display a text description of the DriveType property by using a Switch construct. For example, if the DriveType is 3, display Fixed Disk. Use a search engine to search for Win32_LogicalDisk, and you ll locate the documentation page for that WMI class. The documentation page will display the possible values, and meanings, of the DriveType property.