Drives and Environment Variables

In PowerShell, a drive is a top-level container that represents a hierarchical data structure. These structures can include:

• File systems (e.g., C:\, D:\)

• Registry hives (e.g., HKLM:\, HKCU:\)

• Environment variables (e.g., env:\)

• Certificates (e.g., cert:\)

• Variables (e.g., variable:\)

• Aliases (e.g., alias:\)

• Functions (e.g., function:\)

Each drive is a logical representation of a data store, allowing you to interact with it using familiar commands like Get-ChildItem (aliased as dir or ls).

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Why Use Drives?

The concept of drives simplifies navigation and manipulation of hierarchical data structures. Instead of using different tools for the filesystem, registry, or environment variables, PowerShell provides a unified interface. This consistency reduces the learning curve and makes scripting more intuitive.

For example:

• In the filesystem, you navigate folders and files.

• In the registry, you navigate keys and values.

• In environment variables, you navigate variable names and their values.

PowerShell treats all these structures as "drives," so you can use the same commands (cd, dir, New-Item, etc.) across different data stores.

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Listing Available Drives

To see the drives currently available in your PowerShell session, use the Get-PSDrive command:

Get-PSDrive

This command lists all drives, including filesystem drives (C:, D:), registry drives (HKLM:, HKCU:), and others like env: and cert:.

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Providers: The Backbone of Drives

Each drive is backed by a provider, which is a .NET assembly that exposes a data store to PowerShell. Providers enable PowerShell to interact with different types of data stores in a consistent way.

To list the available providers, use:

Get-PSProvider

Common providers include:

• FileSystem: Manages files and folders.

• Registry: Manages registry keys and values.

• Environment: Manages environment variables.

• Alias: Manages PowerShell aliases.

• Variable: Manages PowerShell variables.

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2. Navigating Drives

Changing Locations

PowerShell provides the Set-Location cmdlet (aliased as cd or chdir) to change your current location within a drive. For example:

cd C:\Windows  # Navigate to the Windows directory
cd HKLM:\Software  # Navigate to the Software registry hive
cd env:  # Navigate to the environment variables drive

You can also use relative paths (. for the current directory, .. for the parent directory) and tab completion for convenience.

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Viewing Contents

To view the contents of a drive or directory, use the Get-ChildItem cmdlet (aliased as dir or ls):

dir C:\  # List files and folders in the root of C:
dir HKLM:\Software  # List registry keys under Software
dir env:  # List all environment variables

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3. Environment Variables in PowerShell

What Are Environment Variables?

Environment variables are dynamic values that affect the behavior of processes and programs running on your system. Examples include:

• PATH: Specifies directories where executable programs are located.

• TEMP: Specifies the directory for temporary files.

• USERNAME: Specifies the current user's name.

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Accessing Environment Variables

In PowerShell, environment variables are accessed through the env: drive. To list all environment variables:

dir env:

To access a specific variable, use the $env: prefix:

$env:PATH  # View the PATH variable
$env:USERNAME  # View the current username

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Modifying Environment Variables

Creating a New Variable

To create a new environment variable:

New-Item -Path env:\MY_VARIABLE -Value "MyValue"

Updating an Existing Variable

To change the value of an existing variable:

Set-Item -Path env:\MY_VARIABLE -Value "NewValue"

Deleting a Variable

To remove an environment variable:

Remove-Item -Path env:\MY_VARIABLE

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Why Environment Variable Changes Are Not Permanent

Changes to environment variables in PowerShell are session-specific. If you close PowerShell, all changes are lost. To make permanent changes, you must modify your system's environment variables through the Control Panel or by editing your PowerShell profile.

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4. Built-In PowerShell Variables

PowerShell automatically creates several variables, known as automatic variables, that provide useful information and functionality. To see a list of these variables:

help about_automatic_variables

Some commonly used automatic variables include:

• $_: Represents the current object in the pipeline.

• $?: Indicates whether the last operation succeeded ($true or $false).

• $HOME: Stores the path to the user's home directory.

• $PROFILE: Stores the path to the user's PowerShell profile script.

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5. Creating Custom Drives

You can create custom drives using the New-PSDrive cmdlet. For example, to map a network share as a drive:

New-PSDrive -Name Share -PSProvider FileSystem -Root \\Server\Share
cd Share:

This creates a new drive called Share: that points to the specified network path.