[c#] How do I get and set Environment variables in C#?

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

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);

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.

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.

Get and Set

Get

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

Set

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

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

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.

Get and Set

Get

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

Set

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

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

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);

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.

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);