All commands are broken down into the command name, the parameters specified to the command, and the arguments to those parameters.

The first element in the command is the name of the command to be executed. The PowerShell interpreter looks at this name and determines what has to be done. It must figure out not only which command to run but which kind of command to run.

In PowerShell, there are four categories of commands:

• cmdlets
• shell function commands
• script commands
• native Windows commands.

Cmdlets

Cmdlet is a term that’s specific to the PowerShell environment. A cmdlet is implemented by a .NET class that derives from the Cmdlet base class in the PowerShell Software Developers Kit (SDK). This category of command is compiled into a dynamic link library (DLL) and then loaded into the PowerShell process, usually when the shell starts up. Because the compiled code is loaded into the process, it’s the most efficient category of command to execute.

 

Functions

Function is a named piece of PowerShell script code that lives in memory while the interpreter is running and is discarded on exit. Functions consist of user-defined code that’s parsed once when defined. This parsed representation is preserved so it doesn’t have to be reparsed every time it’s used.

 

Scripts

A script command is a piece of PowerShell code that lives in a text file with a .ps1 extension. These script files are loaded and parsed every time they’re run, making them somewhat slower than functions to start (although once started, they run at the same speed).

A script takes its name from the name of the file and is delimited by the file itself, so no braces are needed.

 

Native commands (applications)

Running a native command involves creating a whole new process for the command, native commands are the slowest of the command types. Also, native commands do their own parameter processing and so don’t necessarily match the syntax of the other types of commands. Native commands cover anything that can be run on a Windows computer, so you get a wide variety of behaviors. One of the biggest issues is when PowerShell waits for a command to finish but it just keeps on going.