How to Read Windows Environment Variables (System Variables) in a .NET Program - VB.NET Example

Anyone who has written CMD knows about environment variables. They let you easily get information that differs from one computer to another, such as the user name. In CMD, using an environment variable is simple: you just write it in the %environment variable name% format. In a .NET program, though, it isn't that simple. You need to use the Environ function.

Reading Environment Variables in .NET

In .NET, you read system variables with the Environ function. The function is simple to use, and its format is as follows:

Environ("環境變數名稱")

P.S. Note that the environment variable name should be treated as a string, not a variable, so wrap it in double quotes.

Example (console application):

Module Module1
Sub Main()
    Console.WriteLine("CPU核心數:" &amp; Environ("NUMBER_OF_PROCESSORS"))
    Console.ReadLine()
End Sub
End Module

Common Windows Environment Variable Names

Below are some common environment variable names. They're handy for getting information that differs from one computer to another, such as the number of CPU cores or the user name.

SystemRoot	Location of the operating system root directory	C:WINDOWS
ComSpec	Location of CMD	C:WINDOWSsystem32cmd.exe
NUMBER_OF_PROCESSORS	Number of CPU cores	4
TEMP	Location of the system temp folder	C:WINDOWSTEMP
HOMEDRIVE	Drive where the current system is located	C:
HOMEPATH	Shows the folder location of the current user	useradministrator
OS	Name of the operating system in use	Windows NT
ProgramFiles	Location of the ProgramFiles folder	C:ProgramFiles
USERNAME	Current user name	Administrator
COMPUTERNAME	Get the computer name	LINROEX-PC