251

How can I get Environnment variables and if something is missing, set the value?

Joel Coehoorn
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Mister Dev
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9 Answers9

336

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.

Matt
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Patrick Desjardins
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    Also note the optional third parameter: System.Environment.SetEnvironmentVariable (variable, value, **EnvironmentVariableTarget**) Possible values are: *Machine*, *Process* and *User* – Lessan Vaezi Feb 13 '11 at 12:45
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    Does `EnvironmentVariableTarget.Machine` requires Administrator access? – checksum Feb 11 '14 at 06:45
  • Yes, it does. Trying to run it without will result in an obvious exception. – Erez A. Korn May 13 '15 at 04:19
44

Get and Set

Get

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

Set

string setEnv = Environment.SetEnvironmentVariable("envvar", varEnv);
Tom Stickel
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38

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.

Nathan Bedford
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    +1 I had to use this solution because the other one answered by Patrick Desjardins required me to have admin privileges. I was able to read the value of the environment variable without having admin privileges with this solution! – Tono Nam Apr 18 '13 at 15:07
  • @TonoNam Patrick’s answer works in my machine *without* admin privileges. Note that setting System environment variable does require admin privileges (of course). – Franklin Yu Oct 31 '18 at 00:33
  • what about getting the `PATH` variable of the *current user* instead of the _machine_, how to do that? – JobaDiniz Apr 18 '23 at 10:44
18

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);
Tim S. Van Haren
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SpeedyNinja
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8
Environment.SetEnvironmentVariable("Variable name", value, EnvironmentVariableTarget.User);
Karthik Chintala
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2

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();

enter image description here

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.

Vijendran Selvarajah
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2

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);
OfirD
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0

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);
Ajit
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0

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>
D. Kermott
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