PowerShell Cookbook, 4th Edition

Chapter 4. Looping and Flow Control

4.0 Introduction

As you begin to write scripts or commands that interact with unknown data, the concepts of looping and flow control become increasingly important.

PowerShell’s looping statements and commands let you perform an operation (or set of operations) without having to repeat the commands themselves. This includes, for example, doing something a specified number of times, processing each item in a collection, or working until a certain condition comes to pass.

PowerShell’s flow control and comparison statements let you adapt your script or command to unknown data. They let you execute commands based on the value of that data, skip commands based on the value of that data, and more.

Together, looping and flow control statements add significant versatility to your PowerShell toolbox.

4.1 Make Decisions with Comparison and Logical Operators

Problem

You want to compare some data with other data and make a decision based on that comparison.

Solution

Use PowerShell’s logical operators to compare pieces of data and make decisions based on them:

Comparison operators

-eq, -ne, -ge, -gt, -in, -notin, -lt, -le, -like, -notlike, -match, -notmatch, -contains, -notcontains, -is, -isnot

Logical operators

-and, -or, -xor, -not

For a detailed description (and examples) of these operators, see “Comparison Operators”.

Discussion

PowerShell’s logical and comparison operators let you compare pieces of data or test data for some condition. ...