Windows

When working with HTML, it is common to require advanced regular expressions that separate the content you care about from the content you don’t. Aperfect example of this is extracting all the HTML links from a web page.

Problem

You want to download a web page from the Internet and work with the content as a plain string.

Solution

Use the DownloadString() method from the .NET Framework’s System.Net.WebClient class to download a web page or plain text file into a string.

PS >$source = "http://blogs.msdn.com/powershell/rss.xml" PS > PS >$wc = NewObject System.Net.WebClient PS >$content = $wc.DownloadString($source)

Discussion

Problem

You want to download a file from a web site on the Internet.

Solution

Use the DownloadFile() method from the .NET Framework’s System.Net.WebClient class to download a file:

PS >$source = "http://www.leeholmes.com/favicon.ico" PS >$destination = "c:\temp\favicon.ico" PS > PS >$wc = NewObject System.Net.WebClient PS >$wc.DownloadFile($source, $destination)

Discussion

Although PowerShell provides an enormous benefit even when your scripts interact only with the local system, working with data sources from the Internet opens exciting and unique opportunities. For example, you might download files or information from the Internet, interact with a web service, store your output as HTML, or even send an email that reports the results of a longrunning script.

Through its cmdlets and access to the networking support in the .NET Framework, PowerShell provides ample opportunities for Internetenabled administration.

Problem

You want to use Excel to manipulate or visualize the output of a command.

Solution

Use PowerShell’s ExportCsv cmdlet to save the output of a command in a CSV file, and then load that CSV in Excel. If you have Excel associated with .CSV files, the InvokeItem cmdlet launches Excel when you provide it with a .CSV file as an argument.

Example 87 demonstrates how to generate a CSV containing the disk usage for sub directories of the current directory.

Problem

You want to import structured data that has been stored in a CSV file. This is helpful when you want to use structured data created by another program, or structured data modified by a person.

Solution

Use PowerShell’s ImportCsv cmdlet to import structured data from a CSV file.

For example, imagine that you previously exported an inventory of the patches applied to a preVista system by KB number:

cd $env:WINDIR GetChildItem KB*.log | ExportCsv c:\temp\patch_log.csv

Problem

You want to store the output of a command in a CSV file for later processing. This is helpful when you want to export the data for later processing outside PowerShell.

Solution

Use PowerShell’s ExportCsv cmdlet to save the output of a command into a CSV file. For example, to create an inventory of the patches applied to a system by KB number (on preVista systems):

cd $env:WINDIR GetChildItem KB*.log | ExportCsv c:\temp\patch_log.csv

Problem

You have a set of data (such as a hashtable or array) and want to save it to disk so that you can use it later. Conversely, you have saved structured data to a file and want to import it so that you can use it.

Solution

Use PowerShell’s ExportCliXml cmdlet to save structured data to disk, and the ImportCliXml cmdlet to import it again from disk.

For example, imagine storing a list of your favorite directories in a hashtable, so that you can easily navigate your system with a “Favorite CD” function. Example 85 shows this function.

Problem

You want to work with and access information in an XML file.

Solution

Use PowerShell’s XML cast to convert the plaintext XML into a form that you can more easily work with. In this case, the RSS feed downloaded from the Windows PowerShell blog:

PS >$xml = [xml] (GetContent powershell_blog.xml)

Like other rich objects, PowerShell displays the properties of the XML as you explore. These properties are child nodes and attributes in the XML, as shown by Example 81.

In the world of textonly system administration, managing structured files is often a pain. For example, working with (or editing) an XML file means either loading it into an editor to modify by hand, or writing a custom tool that can do that for you. Even worse, it may mean modifying the file as though it were plain text while hoping to not break the structure of the XML itself.