How do cmdlets work?

In contrast to native OS commands such as ps on Linux or tasklist on Windows, PowerShell uses cmdlets. These cmdlets always follow the same, simple syntax. Moreover, specifying parameters and their values always works the same with every cmdlet as well.

This section will help you to understand how cmdlets work before diving into them in later chapters.

Getting ready

In order to follow this recipe, you should have completed the installation of PowerShell Core for your operating system.

How to do it...

Please perform the following steps:

1. Start PowerShell Core.
2. Type New-Item -Path variable: -Name myVariable -Value "Isn't it great?.
3. Type $myVariable. $myVariable is a variable—a temporary storage space for your data. Just executing the variable will place it on the output.
4. Type Get-ChildItem $home *.*. This cmdlet uses no parameter names, and only parameter values. $home is a built-in variable and *.* filters for all files with a dot in the name.
5. Type Get-ChildItem *.txt $home. Observe the error this time. You can't mix positional parameters.
6. Type Get-ChildItem -Filter *.txt -Path $home. By using the parameter names, the cmdlet works again.
7. Type $processName = 'powershell'. Assigning anything to a variable like this will store the result in the variable.
8. Type Get-Process $processName.
9. Type Get-Process $pid. As opposed to the process name, using an ID will fail the cmdlet.
10. Type Get-Process -Id $pid. By using the correct parameter, the cmdlet works again.
11. Type Get-Command -Syntax -Name Get-Process. Observe the syntax of the cmdlet; there's more than one way to execute a cmdlet. These are called parameter sets.

How it works...

Native PowerShell cmdlets should all follow the exact same syntax: verb-noun. The verb indicates the action and the noun indicates the recipient of that action. Whether it is a cmdlet such as New-Item or Get-Process, the syntax always follows the same principle.

With all of its different parameters used, a full cmdlet call might look like the following example:

Get-ChildItem $home -Filter *.txt -File

Get-ChildItem is the name of the cmdlet. $home is the value of a so-called positional parameter, Path. -Filter uses the parameter name, and *.txt is the value provided for that parameter. -File is something called a switch parameter, which resembles a command-line switch.