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PowerShell is not just a command-line tool; its design philosophy, functional architecture, and usage differ significantly from traditional Shells. * * * ## I. Cmdlet: The Smallest Command Unit ### What is a Cmdlet? Cmdlets (pronounced _command-let_) are the most basic command units in PowerShell. They are all .NET-based classes that return one or more **.NET objects** upon execution. ### Naming Convention: Verb-Noun Every Cmdlet follows the **Verb-Noun** naming 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 comes with hundreds of Cmdlets, and third-party modules can define even more. ### Example Get-ServiceGet-ChildItem -Path C:\Windows You can also use `Get-Command` to view all available Cmdlets: Get-Command -CommandType Cmdlet * * * ## II. Object Pipeline ### What's the difference from UNIX/Linux pipes? In traditional Shells, the pipe (`|`) passes text strings. In PowerShell, **the pipeline passes complete .NET objects**. This means you can retain structured data (properties, methods) for subsequent processing. ### Example: Filter processes by CPU usage Get-Process | Where-Object { $_.CPU -gt 100 } | Select-Object Name, CPU In the above command: * `Get-Process` gets all processes (returns objects) * `Where-Object` filters processes with CPU usage greater than 100 * `Select-Object` outputs only the `Name` and `CPU` fields ### The Beauty of Pipeline Passing Values You don't need to use tools like `awk`, `cut`, `grep`, etc., to "parse" the output; instead, you directly manipulate object properties. * * * ## III. Provider and PSDrive: Resource Drive Abstraction PowerShell provides a unified way to access resources: the **Provider model**, which maps various resources to virtual drives (PSDrives), allowing you to operate them just like the `C:` 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: Manipulating the Registry Get-ChildItem HKLM:\Software\Microsoft Browse the registry just like browsing folders. * * * ## IV. Scripts and Modules: Organization and Reuse ### Scripts (.ps1) * PowerShell scripts are text files with the `.ps1` extension * They contain a series of commands, flow control, functions, etc. ### Modules (.psm1 / .psd1) Modules are reusable functional units in PowerShell, which can be: * A `.psm1` file (module script) * A folder containing a `.psd1` manifest (advanced module) Modules support: * **Auto-loading** (automatically loaded when a function within it is used) * **Version control** * **Dependency declaration** View all modules in the system: Get-Module -ListAvailable Import a module: Import-Module Az * * * ## V. Execution Policy To prevent malicious script execution, PowerShell introduces **Execution Policy**, which restricts the execution behavior of `.ps1` script files. ### Common Policy Types | Policy | Meaning | | --- | --- | | Restricted | Default, does not allow any scripts to run | | RemoteSigned | Allows local scripts to run; remote scripts must be signed | | AllSigned | All scripts must be signed | | Bypass | Unrestricted, not recommended for use in production | ### Set Execution Policy Set-ExecutionPolicy RemoteSigned -Scope CurrentUser > ⚠️ Note: Execution policy only affects script files; it does not restrict manually entered commands. * * * ## VI. PowerShell Remoting PowerShell Remoting supports remotely connecting to another computer and executing commands via the **WS-MAN (based on WinRM)** or **SSH** protocol. ### Enable WinRM (on Windows) Enable-PSRemoting -Force ### Common Commands # Establish a remote sessionEnter-PSSession -ComputerName Server01# Execute commands in bulkInvoke-Command -ComputerName Server01,Server02 -ScriptBlock { Get-Service } ### Cross-platform remoting via SSH Enter-PSSession -HostName linux01 -User user1 -SSHTransport * * * ## VII. Desired State Configuration (DSC) DSC (Desired State Configuration) is PowerShell's **declarative configuration platform**, used to define the "ideal state" of a system. It allows you to: * Define resource states using configuration scripts (e.g., a certain service should be running, a certain file should exist) * Automatically configure the machine to that state * Detect drift and automatically remediate ### Usage 1. Write a configuration file (`.ps1`) 2. Compile it into a MOF file 3. Deploy using Push or Pull mode > DSC is particularly suitable for large-scale server configuration, compliance checks, and automated deployment. * * * ## VIII. Command Discovery and Help System PowerShell provides a rich help system that allows you to 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 conceptual documentation (e.g., `about_Execution_Policies`) ### Example: View Object Structure Get-Process | Get-Member * * * ## Summary | Concept | Keyword | Brief Description | | | --- | --- | --- | --- | | Cmdlet | `Verb-Noun` | Smallest execution unit, based on .NET | | | Pipeline | ` | ` | Passes objects instead of text | | Provider | `FileSystem`, `Env:` | Unified access to various resources | | | Module | `.psm1`, `.psd1` | Organize reusable command collections | | | Execution Policy | `Set-ExecutionPolicy` | Control script execution permissions | | | Remoting | `Enter-PSSession` | Execute commands remotely | | | DSC | `Configuration` | Declarative system configuration platform | | | Help System | `Get-Help` | Built-in documentation system |