Using .NET Libraries in PowerShell - Best Practice and Quick Start

Most PowerShell cmdlets are simply wrappers around underlying .NET libraries. In this series, we’ll take a closer look at how these .NET libraries work and how you can access their functionality directly.

This can be very helpful because cmdlets often expose only a fraction of what the underlying .NET library can do. Additionally, there are many useful .NET libraries that are not exposed by any cmdlet at all.

Best Practice

Cmdlets are PowerShell’s way of standardizing commands. They provide help, error handling, and serve as a "civilized" wrapper around .NET, making PowerShell code both powerful and concise.

If a cmdlet exists for the task you need, use it. Avoid replacing it with raw .NET code, as this makes your PowerShell script unnecessarily difficult to read.

That said, if no cmdlet is available for the task, using .NET libraries directly is the best alternative.

Path Management

Let’s take a practical example to explore the relationship between .NET libraries and cmdlets: managing paths is a common task in many scripts.

That’s why PowerShell includes a cmdlet named Split-Path.

$path = "c:\logs\server12.csv"
Split-Path -Path $path             # parent folder
Split-Path -Path $path -Leaf       # file name
Split-Path -Path $path -Qualifier  # drive letter

# new in PowerShell 7
Split-Path -Path $path -LeafBase   # file name without extension
Split-Path -Path $path -Extension  # file extension 

Initially, the cmdlet could not extract the base file name or file extension. In PowerShell 7, it was enhanced with additional parameters. While this is useful, it affects backward compatibility: if you use the new parameters, your script will no longer run in Windows PowerShell.

Visiting .NET

Like most cmdlets, Split-Path is merely a thin wrapper around an underlying .NET library that performs the actual work:

$path = "c:\logs\server12.csv"
[System.IO.Path]::GetDirectoryName($path)              # parent folder
[System.IO.Path]::GetFileName($path)                   # file name
[System.IO.Path]::GetPathRoot($path)                   # drive letter
[System.IO.Path]::GetFileNameWithoutExtension($path)   # file name without extension
[System.IO.Path]::GetExtension($path)                  # file extension 

By using the underlying .NET library directly, you gain access to all the information, regardless of the PowerShell version you are using. PowerShell 7 simply added parameters to expose additional .NET functionality that had always been there, even in Windows PowerShell.

Quick Start: Accessing (Any) .NET Library

The hardest part of using .NET libraries is knowing their names. Once you know a library's name—such as System.IO.Path in the example above—you can easily discover the methods (commands) it offers:

• In your favorite IDE, enclose the library name in square brackets and add two colons: [System.IO.Path]::. IntelliSense will now show the available properties and methods. You may need to press CTRL+SPACE to invoke IntelliSense.
• Once you have selected a method, execute it without parentheses. This will display the method overloads (its help).

PS C:\> [System.IO.Path]::GetExtension

OverloadDefinitions                      
-------------------                      
static string GetExtension(string path)  

Here is how to decipher an overload definition:

static string GetExtension(string path)

• Each method call starts with static, indicating that it is implemented directly in the library.
• Next, you see the data type of the return value. GetExtension() returns a string.
• Then comes the method name: GetExtension in this case.
• Inside parentheses, you see the comma-separated list of arguments that the method requires. Each argument is described by two words: first, the data type of the argument, and second, its name or description. For GetExtension, the method requires one argument, which must be a string representing the path you want to examine.

To list all the properties and methods in a .NET library, use Get-Member with the -Static parameter:

PS C:\> [System.Io.Path] | Get-Member -Static


   TypeName: System.IO.Path

Name                        MemberType Definition                                                                                                                                 
----                        ---------- ----------                                                                                                                                 
ChangeExtension             Method     static string ChangeExtension(string path, string extension)                                                                               
Combine                     Method     static string Combine(Params string[] paths), static string Combine(string path1, string path2, string path3), static string Combine(str...
Equals                      Method     static bool Equals(System.Object objA, System.Object objB)                                                                                 
GetDirectoryName            Method     static string GetDirectoryName(string path)                                                                                                
GetExtension                Method     static string GetExtension(string path)                                                                                                    
GetFileName                 Method     static string GetFileName(string path)                                                                                                     
GetFileNameWithoutExtension Method     static string GetFileNameWithoutExtension(string path)                                                                                     
GetFullPath                 Method     static string GetFullPath(string path)                                                                                                     
GetInvalidFileNameChars     Method     static char[] GetInvalidFileNameChars()                                                                                                    
GetInvalidPathChars         Method     static char[] GetInvalidPathChars()                                                                                                        
GetPathRoot                 Method     static string GetPathRoot(string path)                                                                                                     
GetRandomFileName           Method     static string GetRandomFileName()                                                                                                          
GetTempFileName             Method     static string GetTempFileName()                                                                                                            
GetTempPath                 Method     static string GetTempPath()                                                                                                                
HasExtension                Method     static bool HasExtension(string path)                                                                                                      
IsPathRooted                Method     static bool IsPathRooted(string path)                                                                                                      
ReferenceEquals             Method     static bool ReferenceEquals(System.Object objA, System.Object objB)                                                                        
AltDirectorySeparatorChar   Property   static char AltDirectorySeparatorChar {get;}                                                                                               
DirectorySeparatorChar      Property   static char DirectorySeparatorChar {get;}                                                                                                  
InvalidPathChars            Property   static char[] InvalidPathChars {get;}                                                                                                      
PathSeparator               Property   static char PathSeparator {get;}                                                                                                           
VolumeSeparatorChar         Property   static char VolumeSeparatorChar {get;}  
    

As you see, even the Split-Path cmdlet found in the latest PowerShell version still exposes only a portion of what this .NET library can do. For example, if you need to generate a new filename with a different extension—whether to create a backup or convert a file type—ChangeExtension() can do the heavy lifting:

$path = "c:\logs\server12.csv"

# create a backup file name
[System.Io.Path]::ChangeExtension($path, 'bak')


$path = "c:\music\song1.wav"

# create a new file name for a media converter
[System.Io.Path]::ChangeExtension($path, 'mp3') 

Or, if you want to determine the true path separator on the operating system where your PowerShell instance is running, .NET has the answer:

[System.Io.Path]::PathSeparator
[System.Io.Path]::VolumeSeparatorChar 

On Windows, the path separator is a backslash, while on Linux, it is a forward slash. This allows you to dynamically construct valid paths in heterogeneous environments. This is how Join-Path works in the background.

Related links 

• ScriptRunner ActionPacks provide ready-to-use PowerShell scripts.
• Try out ScriptRunner here
• ScriptRunner: Book a demo with our product experts