Professional Windows® PowerShell

4.4. Working with Object Pipelines

To perform anything but the simplest tasks using Windows PowerShell, you will make use of a pipeline. A pipeline is a series of commands executed in sequence. Importantly, the objects that result from executing the first command in a pipeline are passed to the next command in the pipeline.

In this section, I will introduce several tools that you can use in pipelines.

4.4.1. Sequences of Commands

A pipeline is, essentially, a sequence of commands where objects from one command are passed for processing to later commands in the sequence. The separator between elements in the pipeline is the | symbol. Onscreen it is typically displayed as two separate vertical parts similar to a colon (see the command entered in Figure 4-14 for he onscreen appearance of the pipe symbol).

4.4.2. Filtering Using where-object

In some situations a single cmdlet may retrieve an inconveniently large number of objects. Therefore, you will often want to filter objects, for example for display or sorting. The where-object cmdlet allows you to filter objects according to the condition specified in a script block contained in paired curly brackets. You have seen some examples earlier in this chapter that use the where-object cmdlet. In addition to the -eq operator, which you saw used earlier in the chapter, you have many other operators available for use. These are shown in the following table.

Operator	Meaning
-lt	Less than
-le	Less than or equal to
-gt	Greater than
-ge	Greater ...