PowerShell Core Concepts

PowerShell is not just a command-line tool; its design philosophy, functional architecture, and usage differ significantly from traditional shells.

1. Cmdlet: The Smallest Command Unit

What is a Cmdlet?

A Cmdlet (pronouncedcommand-let) is the most basic command unit in PowerShell. Cmdlets are .NET-based classes that return one or more.NET objects。

Naming Convention: Verb-Noun

Every Cmdlet follows theverb-nounnaming convention, for example:

Cmdlet Meaning
Get-Process Get process information
Set-Item Set the value of a resource item
Remove-Item Delete files, registry keys, etc.
New-User Create a new user (if the AD module is installed)

PowerShell ships with hundreds of Cmdlets, and third-party modules can define many more.

Example

Get-Service
Get-ChildItem -Path C:\Windows

You can also useGet-Commandto view all available Cmdlets:

Get-Command -CommandType Cmdlet

2. Object Pipeline

What's the difference from UNIX/Linux pipes?

In traditional shells, the pipe (|) passes text strings. In PowerShell, however,the pipeline passes complete .NET objects。

This means you can preserve structured data (properties, methods) for further processing.

Example: Filter processes by CPU usage

Get-Process | Where-Object { $_.CPU -gt 100 } | Select-Object Name, CPU

In the above command:

  • Get-ProcessGet all processes (returns objects)
  • Where-ObjectFilter processes with CPU usage greater than 100
  • Select-ObjectOutput only theNameandCPUfield

The beauty of piping objects

You don't need to use tools likeawk、cut、grepto "parse" the output; instead, you work directly with object properties.

3. Providers and PSDrive: Resource Drive Abstraction

PowerShell provides a unified way to access resources:the Provider model, which maps various resources to virtual drives (PSDrive), just likeC:operating a drive.

Common Provider types

Provider Example drive Description
FileSystem C:, D: Local file system
Registry HKLM:, HKCU: Windows Registry
Environment Env: Environment variables
Certificate Cert: Certificate store
Function Function: Functions in the current session
Variable Variable: Currently defined variables
Alias Alias: Command aliases

Example: Working with the registry

Get-ChildItem HKLM:\Software\Microsoft

Browse the registry just like browsing folders.

4. Scripts and Modules: Organization and Reuse

Scripts (.ps1)

  • PowerShell scripts are text files with the.ps1extension
  • They contain a series of commands, flow control, functions, etc.

Modules (.psm1 / .psd1)

A module is a reusable functional unit in PowerShell. It can be:

  • a.psm1file (module script)
  • a folder containing a.psd1manifest (advanced module)

Modules support:

  • Auto-loading(automatically loaded when its functions are used)
  • Versioning
  • Dependency declarations

View all modules in the system:

Get-Module -ListAvailable

Import a module:

Import-Module Az

5. Execution Policy

To prevent malicious scripts from running, PowerShell introduced theexecution policy(Execution Policy), which restricts.ps1the execution behavior of script files.

Common policy types

Policy Meaning
Restricted Default; no scripts are allowed to run
RemoteSigned Allows local scripts to run; remote scripts must be signed
AllSigned All scripts must be signed
Bypass Unrestricted; not recommended for production

Setting the execution policy

Set-ExecutionPolicy RemoteSigned -Scope CurrentUser

⚠️ Note: The execution policy only affects script files; it does not restrict manually entered commands.

6. Remote Management (PowerShell Remoting)

PowerShell Remoting supports connecting to another computer remotely and executing commands via theWS-MAN (based on WinRM)orSSHprotocol.

Enabling WinRM (on Windows)

Enable-PSRemoting -Force

Common commands

# 建立远程会话
Enter-PSSession -ComputerName Server01

# 批量执行命令
Invoke-Command -ComputerName Server01,Server02 -ScriptBlock { Get-Service }

Cross-platform remoting with SSH support

Enter-PSSession -HostName linux01 -User user1 -SSHTransport

7. Desired State Configuration (DSC)

DSC (Desired State Configuration) is PowerShell'sdeclarative configuration platform, used to define the "desired state" of a system.

It allows you to:

  • Define resource states with configuration scripts (e.g., a service should be running, a file should exist)
  • Automatically configure the machine to that state
  • Detect drift and automatically remediate it

How to use it

  1. Write a configuration file (.ps1）
  2. Compile it into a MOF file
  3. Deploy using Push or Pull mode

DSC is especially useful for large-scale server configuration, compliance checks, and automated deployment.

8. Command Discovery and Help System

PowerShell provides a rich help system that lets you easily explore commands:

  • Get-Help Get-Process: View command help
  • Get-Command: List all commands
  • Get-Member: View object properties and methods
  • Get-Help about_*: View built-in knowledge documents (such asabout_Execution_Policies）

Example: Viewing object structure

Get-Process | Get-Member

Summary

Concept Keyword Brief description
Cmdlet verb-noun Smallest execution unit, based on .NET
Pipeline ` ` Passes objects rather than text
Provider FileSystem, Env: Unified access to various resources
Module .psm1, .psd1 Organizes reusable command collections
Execution policy Set-ExecutionPolicy Controls script execution permissions
Remote management Enter-PSSession Execute commands remotely
DSC Configuration Declarative system configuration platform
Help system Get-Help Built-in documentation system
Other extensions