Prof. Powershell

Function Fun

Have a blast stringing along functions and reusing them.

• By Jeffery Hicks
• 06/02/2009

Your Windows PowerShell session has a wealth of functionality. In addition to cmdlets, PowerShell loads a number of functions when you launch your console. If you define additional functions, from the command prompt, through your profile or by dot-sourcing a script, these functions are also ready for you to use.

To see what functions are available, simply peruse your Function: drive, like this:

PS C:\ dir function:

To examine a specific function, use Get-ChildItem.

PS C:\ dir function:mkdir

That doesn't show much information. So try this:

PS C:\ dir function:mkdir | Select * | More

Now we're talking. I pipe the result to more because a lot of information might scroll by pretty quickly; although usually I'm only interested in a function's definition. That is easy to get since definition is merely a property:

PS C:\ (dir function:mkdir).Definition

Here's where this can come in handy. Suppose you create a new function in the shell:

PS C:\> function dirdate {
>> param ([string]$path=".",
>>        [switch]$recurse,
>>        [switch]$descending )if ($recurse) {
>>        $files= dir $path -recurse
>>        }
>>   else {
>>   $files=dir $path
>>   }
>>
>> if ($descending) {
>>   $files | sort LastwriteTime -descending
>>   }
>> else {
>>   $files
>>   }
>> }

Now you'd like to save this function so you can re-use it in future PowerShell sessions. Here's a one-liner that will get the job done:

PS C:\> (dir function:dirdate).definition.Split("'n")| foreach -begin {"Function DirDate { 'n" | out-file dirdate.ps1} -Process {$_ | out-file dirdate.ps1 -append} -end {"}" | out-file dirdate.ps1 -append}

I can create a working script with less code but the formatting leaves something to be desired. This command gets the function definition, which is normally stored as a string. I split it at the new line and pipe this to ForEach-Object. Before I process anything, I create the first part of the file -- that is, the function keyword and name. Then each line from the definition is appended to the file. After all lines have been processed I append the closing “}”. Now, wasn't that fun?