Last week, I dropped by to be interviewed on the PowerScripting Podcast. We chatted about providers, eventing, transactions, security, and a whole slew of V2 improvements that you probably didn’t know about!

Give it a listen: http://powerscripting.wordpress.com/2009/09/27/episode-85-lee-holmes-talks-about-v2/

Call me as shocked as anybody, but the iPhone app store now has a new entry:

Although I can’t find any official information about it on the rest of the internet, O’Reilly has teamed up with Lexcycle (authors of the Stanza iPhone book reading application) to create iPhone applications for many of the top O’Reilly cookbooks.

Just when you thought the “PowerShell Pocket Reference” was a good value per pound, this one comes in at a net weight of zero! Definitely a pocket-sized reference worth carrying around.

Note: As you browse through the book, many of the code samples are cut off by the default zoom. To see the code in its entirety, use the familiar iPhone pinch + zoom gestures to zoom in and out.

Sometimes, people ask, “What’s the equivalent of NET HELPMSG” in PowerShell?

NET HELPMSG is probably the easiest to remember (and works in PowerShell of course,) but PowerShell improves the experience a bunch by way of the .NET Framework.

Suppose you get error 0x80070652 from an installer:

C:\Users\leeholm>net helpmsg 0x80070652
The syntax of this command is:

NET HELPMSG
message#

Oops, it doesn’t support hex. You need to take the last 4 digits:

C:\Users\leeholm>net helpmsg 0652
0652 is not a valid Windows network message number.

More help is available by typing NET HELPMSG 3871.

Oops, forgot to convert it to decimal.

C:\Users\leeholm>set /a c = 0x652
1618
C:\Users\leeholm>net helpmsg 1618

Another installation is already in progress. Complete that installation before proceeding with this install.

Perfect.

No matter your preference, PowerShell makes this easier. The System.ComponentModel.Win32Exception class supports constructors for all of the main scenarios, so PowerShell’s type casting support gives another way (albeit with a slightly ungainly syntax:)

[D:\documents\tools]
PS:163 > [ComponentModel.Win32Exception] 0x80070652
Another installation is already in progress. Complete that installation before proceeding with this install

[D:\documents\tools]
PS:164 > [ComponentModel.Win32Exception] 0x80070652
Another installation is already in progress. Complete that installation before proceeding with this install

[D:\documents\tools]
PS:165 > [ComponentModel.Win32Exception] –2147023278
Another installation is already in progress. Complete that installation before proceeding with this install

[D:\documents\tools]
PS:166 > [ComponentModel.Win32Exception] 0x0652
Another installation is already in progress. Complete that installation before proceeding with this install

[D:\documents\tools]
PS:167 > [ComponentModel.Win32Exception] 1618
Another installation is already in progress. Complete that installation before proceeding with this install

So don’t go replacing all of your NET HELPMSG muscle memory, but when you find yourself struggling with the requirements, give the [ComponentModel.Win32Exception] class a try.

I wanted to download a photo album from Facebook, but of course there’s no simple API or option to do that. Searching the internet finds a couple of options (a Firefox plugin, a Facebook app,) but I couldn’t seem to find anything standalone.

This gives another great opportunity to talk about advanced HTTP scripting in PowerShell. We’ve talked about it in the past (here: http://www.leeholmes.com/blog/AdvancedHTTPASPNetScriptingWithPowerShell.aspx,) so this script introduces some new techniques.

There are a couple of challenges for scripting Facebook, especially using the techniques in the earlier post.

The first is that the login sequence is secure 🙂 The login page gets served over SSL, meaning that the basic Send-TcpRequest commands we did previously won’t work. SSL requires encryption and a complex handshake. Luckily the System.Net.WebClient class provides that for use.

The second issue is that the cookies are dynamic, and given out in two stages. You need to first connect to the main Facebook homepage, at which point you get a couple of session cookies. Then, you connect to the login page, at which point you get some login cookies. Once you have THOSE, you can script the rest of Facebook.

Here is Get-FacebookCookie.ps1:

The most complex part of that script comes from the Set-Cookie headers returned by the server. Information in that header limits the domain of the cookie, expiration dates, and more. Browsers use this information to determine cookie policies, but we want to just blindly feed it back to Facebook. The little match, replace, and join combination converts the “Set-Cookie” syntax into one suitable to return to the server.

Once we’ve logged into Facebook, we download the album page, cycling through successive pages until we stop finding photos to download. Since you can derive the URL to the large size images from the thumbnails, we don’t need to do an extra request for the photo information page. If you wanted to extract photo comments as well, then you would have to.

Here is Get-FacebookAlbum.ps1:

So in under 100 lines of code, we�
�ve got ourselves an image downloader.