Emil’s Blog

This is an example of how to do script parameter parsing in PowerShell:

Pretty neat, huh?

/Emil

As a simple example of working with culture information in PowerShell, here's how to list Swedish monthnames:

The result is an array:

Try doing that in a BAT file...

/Emil

Here's a small script to kill all Word or Excel-processes that have been running for more than 5 minutes. This can be useful on a server that launches those applications to generate documents. You probable shouldn't do it that way but if you do you're likely to discover that the processes don't always terminate as they should. In those situations, scripts like this come in handy.

/Emil

Here's a small example of how to use PowerShell to pretend it's a web browser to login to a service. In my case it's used to let my computer get access to a customer's network, but it could also be used to login to other services, such as public WiFi services, etc. It also serves as an example of how to do a HTTP POST operation in PowerShell, something that can be very useful in many situations.

The code is very simple:

• The script takes two parameters, $username and $password. Note the use of default values to get the logged in user's username into $username (if it's not given by the caller) and mark $password as required (an exception is thrown if the parameter is not given). The last in particular is not very obvious if you ask me.
• We then initialize a normal .Net NameValueCollection with the names and values of the fields to post (i.e. names of the input elements in the HTTP form we're imitating)
• The actual HTTP-posting is done using the UploadValues method of System.Net.WebClient object.

I think simple examples like this really shows the potential of PowerShell and that making .Net types so easily accessible in the language was a really smart design desicion by the language designers.

/Emil

Executing a PowerShell script from outside PowerShell (for example via a Windows shortcut) can be a little complicated, especially if the path to the script contains spaces and it has parameters, so here's how to do it:

Note that I'm using the PowerShell & operator to execute the script. This is because I have to surround the path with quotes so that it's interpreted by PowerShell as a single literal even though it contains spaces. If I would leave out the "&" then the quoted string would simply be interpreted as a string literal to output, so the script would not be executed.

The parameters to the script should not be included within the single quotes since they are not part of the first literal, which should only contain the path to the script to execute.

/Emil

Here's how to list, start and stop Windows services on a remote computer using PowerShell:

This can come in really handy in deployment scripts, etc.

(Parts of this post came from The PowerShell Guy).

/Emil

Update: In the earlier version of this post I used new-object every time I needed a reference to the service. That's not necessary, it's much prettier to use a variable for the reference, so I have now updated the code.

It's quite easy to load and use .Net assemblies in Windows PowerShell, which of course is one of the main selling points of the script language. In this post I'll show a few examples.

Listing all loaded assemblies:

To load a new assembly, do the following:

When an assembly has been loaded, types and code in it can be used with the new-object Cmdlet, for example:

Pretty cool, huh? (BTW, Validate() is a method on the "Affär" class.)

Also note that some command completion works with imported types. For example, if I type "$obj." and then press TAB, then the console will cycle through the available members of the type in question.

There's more to write about this interesting subject, so more posts will come...

/Emil

I recently decided to start learning the (fairly) new Windows PowerShell script language and thought it would be useful to write down some of its pecularities. The list below is by no means complete, it's just my own notes when learning the language.

BTW, I'm quite impressed of the power of this script language and will be using it from now on instead of the good old CMD.EXE and BAT files. However, there is a learning curve involved and it's steeper than it could have been. The creators' idea of "elastic syntax" (you can write the same logic in many ways) doesn't exactly help... Thus there is a need for a reference like this one.

Here we go:

Setup
To allow script execution, do this:

Virtual drives
More things than files can be accessed using a file system-like method using the virtual drives mechanism.

• cert:
• env:
• function:
• HKCU:
• HKLM:
• variable:

Example:

Error handling
PowerShell has a quite powerful error handling arsenal.

Errors can be trapped:

The first example uses the $_ variable to access the ErrorRecord object of the current error, and the second example displays the underlying .Net exception (including call stack, etc).

The previous errors are stored in the $errors array.

Using the console
Display text in the console (and don't send it down the pipeline):

Send text to stderr:

Change the console prompt:

The prompt function should return a single string.

Special operators

Hash tables (object imitations)

Constants
These are fairly self-explanatory:

• $true
• $false
• $null

Built-in variables

• $_ - "current" object variable used in many contexts, i.e. foreach-object and where-object Cmdlets
• $home - current user's home directory
• $profile - path to the current user's profile script in PowerShell (executed at PowerShell startup). NB: This script does not necessarily exist!
• $OFS - Output Field Separator, used when converting lists to strings. Example:
  $OFS="|";[string] @(1,2,3)

• $matches - hash table contained matches after wildcard or regex pattern matching
• $args - parameter array for a function or script
• $input - input object array for functions in a pipeline
• $error - array of errors (error[0] is the latest one)
• $? - boolean error status of last command
• $LastExitCode - exit code of the last command or EXE
• $host - reference to the application hosting PowerShell. $host.ui is useful for reading/writing text to and from the console
• $foreach - enumerator in foreach statement
• $switch - enumerator in switch statement

Pattern matching
Wildcard matching (true/false):

Regular expressions (true/false + matching results in $matches):

Discarding output of a command

Any of the following will do the trick:

Conditional and looping statements

The switch statement is mighty cool:

That's it for now. I will probably extend this posting later as i discover more things that are difficult to remember...

/Emil