Sorting and filtering

One of the great features of PowerShell is its ability to sort and filter objects. This filtering can be used to limit a larger result set and reporting only the information necessary.

This section will review several methods of filtering and sorting data.

How to do it...

1. To explore the filtering capabilities of PowerShell, we look at the running processes on our computer. We then use the Where clause to filter the results.

   Get-Process | Where-Object {$_.Name -eq "chrome"}
   Get-Process | Where-Object Name -eq "chrome"
   Get-Process | Where-Object Name -like "*hrom*"
   Get-Process | Where-Object Name -ne "chrome"  
   Get-Process | Where-Object Handles -gt 1000

2. To view sorting in PowerShell, we again view the processes on our computer and use Sort-Object to change the default sort order.

   Get-Process | Sort-Object Handles
   Get-Process | Sort-Object Handles -Descending
   Get-Process | Sort-Object Handles, ID –Descending

3. To explore the select features of PowerShell, we use Select-String and Select-Object clause:

   Select-String -Path C:\Windows\WindowsUpdate.log -Pattern "Installing updates"
   Get-Process | Select-Object Name -Unique 

4. To view the grouping capabilities of PowerShell, we use Format-Table with the –GroupBy command:

   Get-Process | Format-Table -GroupBy ProcessName  

How it works...

In the first section, we review various methods of filtering information using the Where clause:

• The first method uses the PowerShell Where-Object clause format. The $_ identifier represents the object being passed through the pipe, so $_.Name refers to the Name property of the object. The –eq is an equals parameter that instructs Where-Object to compare the two values.

• The second method performs the same task as the first but uses a parameter format that is new in PowerShell 3.0. In this method the Where-Object comparison no longer needs to use $_ to reference the object being passed, and we no longer need the curly braces {}.

  Note

  Even though the second method shown can often be easier to use and easier to understand, it is important to know both methods. The first method is still in use by PowerShell scripters, and there are some situations that work better using this method.

• The last three methods perform similar comparisons using different parameter. The –like parameter allows for the use of the wildcard character * allowing for less exact filtering. The –ne parameter means not equal and is the exact opposite of the equals parameter. And the –gt parameter means greater than and compares the attribute value to a known value.

The second section uses the Sort-Object command to sort and organize the object attributes. In this section, we show sorting by the handles attribute in both ascending (the default method), and descending format. Additionally, we see that multiple attributes can be sorted at the same time.

The third section uses the Select-String and Select-Object commands to restrict what is returned. The first method searches the WindowsUpdate.log for the string Installing updates and returns the results. The second method takes the output of Get-Process and filters it to only return a unique list of named processes.

The fourth section shows how to perform grouping based on an attribute. The Format-Table command includes a property named –GroupBy that, instead of returning a single table, will return multiple tables. In this case, for each unique ProcessName, a separate table is returned.