如何在 C# 中获取和设置环境变量？

Question

如何获取环境变量，如果缺少某些内容，请设置值？

Answer 1

Use the System.Environment class.

The methods

var value = System.Environment.GetEnvironmentVariable(variable [, Target])

and

System.Environment.SetEnvironmentVariable(variable, value [, Target])

will do the job for you.

The optional parameter Target is an enum of type EnvironmentVariableTarget and it can be one of: Machine , Process , or User . If you omit it, the default target is the current process.

Answer 2

I ran into this while working on a .NET console app to read the PATH environment variable, and found that using System.Environment.GetEnvironmentVariable will expand the environment variables automatically.

I didn't want that to happen...that means folders in the path such as '%SystemRoot%\\system32' were being re-written as 'C:\\Windows\\system32'. To get the un-expanded path, I had to use this:

string keyName = @"SYSTEM\CurrentControlSet\Control\Session Manager\Environment\";
string existingPathFolderVariable = (string)Registry.LocalMachine.OpenSubKey(keyName).GetValue("PATH", "", RegistryValueOptions.DoNotExpandEnvironmentNames);

Worked like a charm for me.

Answer 3

Get and Set

Get

string getEnv = Environment.GetEnvironmentVariable("envVar");

Set

string setEnv = Environment.SetEnvironmentVariable("envvar", varEnv);

Answer 4

This will work for an environment variable that is machine setting. For Users, just change to User instead.

String EnvironmentPath = System.Environment
                .GetEnvironmentVariable("Variable_Name", EnvironmentVariableTarget.Machine);

Answer 5

Environment.SetEnvironmentVariable("Variable name", value, EnvironmentVariableTarget.User);

Answer 6

In Visual Studio 2019 -- Right Click on your project, select Properties > Settings, Add a new variable by giving it a name (like ConnectionString), type, and value. Then in your code read it so:

var sConnectionStr = Properties.Settings.Default.ConnectionString;

These variables will be stored in a config file (web.config or app.config) depending upon your type of project. Here's an example of what it would look like:

  <applicationSettings>
    <Testing.Properties.Settings>
      <setting name="ConnectionString" serializeAs="String">
        <value>data source=blah-blah;etc-etc</value>
      </setting>
    </Testing.Properties.Settings>
  </applicationSettings>

Answer 7

I could be able to update the environment variable by using the following

string EnvPath = System.Environment.GetEnvironmentVariable("PATH", EnvironmentVariableTarget.Machine) ?? string.Empty;
if (!string.IsNullOrEmpty(EnvPath) && !EnvPath .EndsWith(";"))
    EnvPath = EnvPath + ';';
EnvPath = EnvPath + @"C:\Test";
Environment.SetEnvironmentVariable("PATH", EnvPath , EnvironmentVariableTarget.Machine);

Answer 8

If the purpose of reading environment variable is to override the values in the appsetting.json or any other config file, you can archive it through EnvironmentVariablesExtensions .

var builder = new ConfigurationBuilder()
                .AddJsonFile("appSettings.json")
                .AddEnvironmentVariables(prefix: "ABC_")

var config = builder.Build();

According to this example, Url for the environment is read from the appsettings.json. but when the AddEnvironmentVariables(prefix: "ABC_") line is added to the ConfigurationBuilder the value appsettings.json will be override by in the environement varibale value.

Answer 9

Environment variables can also be placed in an application's app.config or web.config file, by their name bounded with percentages ( % ), and then expanded in code.

• Note that when a value of an environment variable is changed (or a new one is set), Visual Studio should be closed and reopened.

For example, in app.config :

<connectionStrings>
    <add name="myConnectionString" connectionString="%DEV_SQL_SERVER_CONNECTION_STRING%" providerName="System.Data.SqlClient" />
</connectionStrings>

And then in the code:

string connectionStringEnv = ConfigurationManager.AppSettings["myConnectionString"];
string connectionString = System.Environment.ExpandEnvironmentVariables(connectionStringEnv);