Huddled Masses

Posts Tagged ‘Filters’

Someone asked a question in the #PowerShell channel on irc.FreeNode.net today about how to use filters, and pasted this an example like this:

The question was: why doesn’t this have any output? Well, the answer is: it can’t have any output. The filter outputs true or false for each item passed into it, but the where scriptblock doesn’t actually pass anything into the filter! Of course we quickly fixed his problem the right way by rewriting the filter to output the items, and getting rid of the where-object call completely … but when I started wondering where he had gotten the bizarre idea to use a filter like that, his answer was: “I read about_filter.” So I went and looked, and sure enough, the example pasted above is straight out of about_filter. And it’s as wrong as it can possibly be.

Let me fix it, and then offer some clarification below. In about_filter there is an example like this: Get-Process | where {$_.processname -like "[a-m]*"} and then a table describing each element of the Where-Object command, and just below it, there is some text about the filter command. Mentally replace that text with this: Read the rest of this entry »