Prof. Powershell

Perfect Properties

PowerShell custom properties go beyond the call of duty by providing information as you need it.

• By Jeffery Hicks
• 04/07/2009

Because PowerShell is an object-oriented shell, it offers a wealth of information. Pipe any object to Get-Member to discover its properties and methods. Once you know an object's properties, you can display them using Select-Object, even if you don't see them in the default view:

PS C:\> get-process | Select Name,ID,StartTime,Path

But you aren't limited to the property list you see with Get-Member. If you can create a PowerShell expression that will return a value for a given object, you can create a custom property for it.

Say you want to display a property called Uptime for a process object. There is pre-defined property. But we can calculate a value by subtracting the StartTime from the current time and returning a timespan object.
First we'll test the basic code with a single process:

PS C:\> (get-date)-(get-process taskmgr).starttime

Days              : 12
Hours             : 7
Minutes           : 41
Seconds           : 43
Milliseconds      : 883
Ticks             : 10645038835764
TotalDays         : 12.3206468006528
TotalHours        : 295.695523215667
TotalMinutes      : 17741.73139294
TotalSeconds      : 1064503.8835764
TotalMilliseconds : 1064503883.5764

We'll simplify by converting this to a string.

PS C:\> ((get-date)-(get-process taskmgr).starttime).ToString()
12.07:46:21.7045890

Now we need to do this for every process instead of just Task Manager. We'll use Select-Object and a hash table, also known as an associative array, to create a custom property and value. The format of the hash table is

@{name="propertyname";expression={powershell code}}

We will use $_ to represent the current object in the pipeline:

@{name="Uptime";Expression={((get-date)-$_.starttime).ToString()}}

This expression can be used like any other property name:

PS C:\> get-process | Select Name,ID,StartTime,@{name="Uptime";Expression={((get-date)-$_.starttime).ToString()}},Path

This also means we can use this new property in the pipeline like any other property:

PS C:\> get-process | where {$_.StartTime -and $_.name -ne "System"} | Sort StartTime -descending | Select Name,ID,,Path,StartTime,@{name="Uptime";Expression={((get-date)-$_.starttime).ToString()}}| Export-csv process-uptime.csv

This expression will export the standard Name, ID, Path and Starttime properties along with the custom Uptime and export the information to a CSV file.

By the way, I've inserted a Where-Object filter to remove any processes that don't have a start time, usually system-related, as well as the System process itself.

I use this technique all the time to provide extra and useful information. Next time, I'll show you a similar technique with the formatting cmdlets.