How can I get Environnment variables and if something is missing, set the value?
9 Answers
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.
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.
2Get and Set
Get
string getEnv = Environment.GetEnvironmentVariable("envVar");Set
string setEnv = Environment.SetEnvironmentVariable("envvar", varEnv);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);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.
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>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);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); 
