It is really easy to get a environment value if it exists or a default value by using the elvis operator in kotlin:

    var envVar: String = System.getenv(&quot;varname&quot;) ?: &quot;default_value&quot;

You could always go down this approach:

    val envVar : String? = System.getenv(&quot;varname&quot;)

Though, to be fair, this doesn&#39;t feel particularly idiomatic, as you&#39;re leveraging Java&#39;s System class, not Kotlin&#39;s.

And if you want to handle env var which do exists but is empty:

```
val myEnv = (System.getenv(&quot;MY_ENV&quot;) ?: &quot;&quot;).ifEmpty { &quot;default_value&quot; }
```

(see edit history for previos versions)


You can use the kotlin extension Konfig 

[Konfig - A Type Safe Configuration API for Kotlin][1]

Konfig provides an extensible, type-safe API for configuration properties gathered from multiple sources — built in resources, system properties, property files, environment variables, command-line arguments, etc.

For example: `Key(&quot;http.port&quot;, intType)`


  [1]: https://github.com/npryce/konfig

I am using redux with `connect` and `redux-thunk` middleware and containers.

Currently when an user perform an action, example one click on a button, I need to dispatch that action (sync) which will dispatch other few actions (asynch).

I am aware dispatching actions from within the reducer is an anti pattern.

I would like to know what is a suitable place for this code. 

Currently I am not sure if it should stay in:

- The action creator.
- In the container using store.subscribe.


Where to dispatch multiple actions in redux?

Just threw together a simple test, not for any particular reason other than I like to try to have tests for all my methods even though this one is quite straightforward, or so I thought.

        [TestMethod]
        public void Test_GetToolRating()
        {
            var rating = GetToolRating(45.5, 0);
            Assert.IsNotNull(rating);
        }
       

        private static ToolRating GetToolRating(double total, int numberOf)
        {
            var ratingNumber = 0.0;

            try
            {
                var tot = total / numberOf;
                ratingNumber = Math.Round(tot, 2);
            }
            catch (Exception ex)
            {
                var errorMessage = ex.Message;
                //log error here
                //var logger = new Logger();
                //logger.Log(errorMessage);
            }

           
            return GetToolRatingLevel(ratingNumber);
        }

As you can see in the test method, I AM dividing by zero. The problem is, it doesn&#39;t generate an error. See the error window display below.

[![Error List View from VS2017][1]][1]


  [1]: https://i.stack.imgur.com/Fjx6O.png

Instead of an error it is giving a value of infinity? What am I missing?So I googled and found that doubles divided by zero DON&#39;T generate an error they either give null or infinity. The question becomes then, how does one test for an Infinity return value?

Divide by zero and no error?

I&#39;d like to get a certain value from an environment variable in my Kotlin app, but I can&#39;t find anything about reading environment variables in the [core libraries](https://kotlinlang.org/api/latest/jvm/stdlib/index.html) documentation.  

I&#39;d expect it to be under [kotlin.system](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.system/index.html) but there&#39;s really not that much there.


How to read an environment variable in Kotlin?

<p>I'd like to get a certain value from an environment variable in my Kotlin app, but I can't find anything about reading environment variables in the <a href="https://kotlinlang.org/api/latest/jvm/stdlib/index.html" target="_blank" rel="noopener noreferrer">core libraries</a> documentation.</p>
<p>I'd expect it to be under <a href="https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.system/index.html" target="_blank" rel="noopener noreferrer">kotlin.system</a> but there's really not that much there.</p>


What is the best way to read **environment variables** in **SpringBoot**?&lt;br&gt;
In Java I did it using:

    String foo = System.getenv(&quot;bar&quot;);

Is it possible to do it using `@Value` annotation?

Read environment variable in SpringBoot

How can I hide my passwords and other sensitive environment variables on-screen in Laravel&#39;s whoops output?

Sometimes other people are looking at my development work. I don&#39;t want them to see these secrets if an exception is thrown, but I also don&#39;t want to have to keep toggling debug on and off, or spin up a dedicated site just for a quick preview.

[![whoops output screenshot with passwords shown][1]][1]


  [1]: https://i.stack.imgur.com/A9vD6.png

How to hide .env passwords in Laravel whoops output?

I have an application that depends on environmental variables like:

&lt;!-- language: js --&gt;

    const APP_PORT = process.env.APP_PORT || 8080;

And I would like to test that for example:

- APP_PORT can be set by a Node.js environment variable.
- or that an [Express.js][1] application is running on the port set with `process.env.APP_PORT`

How can I achieve this with Jest? Can I set these `process.env` variables before each test or should I mock it somehow maybe?

  [1]: https://en.wikipedia.org/wiki/Express.js





Test process.env with Jest

Could you please help me, how to setup environment variables in visual studio code?

Is there any way to set environment variables in Visual Studio Code?

One of our Apps [`github-backup`](https://github.com/dwyl/github-backup) requires the use of an RSA Private Key as an Environment Variable.

Simply attempting to export the key it in the terminal e.g:
```text
export PRIVATE_KEY=-----BEGIN RSA PRIVATE KEY-----
MIIEpAIBAAKCAQEA04up8hoqzS1+
...
l48DlnUtMdMrWvBlRFPzU+hU9wDhb3F0CATQdvYo2mhzyUs8B1ZSQz2Vy==
-----END RSA PRIVATE KEY-----
```

Does not work ... because of the line breaks.

I did a bit of googling but did not find a workable solution ... &lt;br /&gt;
e.g: https://stackoverflow.com/questions/43082918/how-to-sett-multiline-rsa-private-key-environment-variable-for-aws-elastic-beans

![image](https://user-images.githubusercontent.com/194400/37850998-2f87b140-2ed5-11e8-8350-c003c2768e1f.png)

Error:
```
-----END RSA PRIVATE KEY-----&#39;: not a valid identifier
```

followed the instructions in: 
http://blog.vawter.com/2016/02/10/Create-an-Environment-Variable-from-a-Private-Key 

Created a file called `keytoenvar.sh` with the following lines:

    #!/usr/bin/env bash
    file=$2
    name=$1
    export $name=&quot;$(awk &#39;BEGIN{}{out=out$0&quot;\n&quot;}END{print out}&#39; $file| sed &#39;s/\n$//&#39;)&quot;


![image](https://user-images.githubusercontent.com/194400/37851077-76edb4da-2ed5-11e8-8872-ea75be0217a0.png)
then ran the following command:

    source keytoenvar.sh PRIVATE_KEY ./gitbu.2018-03-23.private-key.pem

That _works_ but it seems like a &quot;_long-winded_&quot; approach ... &#129300; 

Does anyone know of a _simpler_ way of doing this? &lt;br /&gt;
(_I&#39;m hoping for a &quot;**beginner friendly**&quot; solution without too many &quot;steps&quot;..._) 

How to Export a Multi-line Environment Variable in Bash/Terminal e.g: RSA Private Key

How can I represent a &quot;many to many&quot; relation with `Room`? My column names are also the same.

e.g. I have `Guest` and `Reservation`. `Reservation` can have many `Guest`&#39;s and a `Guest` can be part of many Reservations. 

Here are my entity definitions:

    @Entity data class Reservation(
        @PrimaryKey val id: Long,
        val table: String,
        val guests: List&lt;Guest&gt;
    )

    @Entity data class Guest(
        @PrimaryKey val id: Long,
        val name: String,
        val email: String
    )

While looking into docs I came across [`@Relation`][1]. I found it really confusing though.

According to this I would want to create a POJO and add the relationships there. So, with my example I did the following:

    data class ReservationForGuest(
        @Embedded val reservation: Reservation,
        @Relation(
            parentColumn = &quot;reservation.id&quot;, 
            entityColumn = &quot;id&quot;, 
            entity = Guest::class
        ) val guestList: List&lt;Guest&gt;
    )

With above I get the compiler error:

```
&gt; Cannot figure out how to read this field from a cursor.
```

I wasn&#39;t able to find a working sample of `@Relation`.

  [1]: https://developer.android.com/reference/android/arch/persistence/room/Relation.html

How can I represent a &quot;many to many&quot; relation with Android Room when column names are same?

I am defining like a instance variable in `kotlin` and want to initialize it `onCreate` method of an `activity`. 

    var count: Int
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        count.inc()
    }

Here I am getting a below error on count variable. 

&gt; Property must be initialized or be abstract in Kotlin

Well, I read this thread https://stackoverflow.com/questions/33849811/property-must-be-initialized-or-be-abstract and tried same but again I am getting a below error.

&gt; lateinit modifier is not allowed on primitive type properties

    lateinit var count: Int
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        count.inc()
    }

Is there any way to do this in `Kotlin` ?

lateinit modifier is not allowed on primitive type properties in Kotlin

I know that data class are like simple models in kotlin with getters and setter by default and are as simple this:
 
    data class User(val name: String, val age: Int)
  
Is it possible to declare a second constructor for that data class?

Can Kotlin data class have more than one constructor?

I have a set of data classes that share some common fields, So ideally I&#39;d like to declare those in a supertype (Message in this example), and be able to write functions that operate on the supertype if they need access to these common fields (messageId in this example).

    fun operate(m: Message) {
      use(m.messageId)
    }

I tried to accomplish this by extending my data classes from a sealed class.

Data classes may extend sealed classes, but not I&#39;m not sure how/if they can accept arguments required by the &quot;supertype&quot; sealed class.

1. Extending a regular class from a sealed class compiles just fine.

        sealed class Message(val messageId: String)
    
        class Track(val event: String, messageId: String): Message(messageId)

2. However, changing it to a data class doesn&#39;t compile (&quot;Data class primary constructor must have only property (val/var) parameters.&quot;).

        sealed class Message(val messageId: String)
    
        data class Track(val event: String, messageId: String): Message(messageId)

3. Declaring the parameter as a property also doesn&#39;t compile (&quot;&#39;messageId&#39; hides member of supertype &#39;Message&#39; and needs &#39;override&#39; modifier&#39;&quot;).

        sealed class Message(val messageId: String)
    
        data class Track(val event: String, val messageId: String): Message(messageId)

4. Opening the supertype property and overriding it in each of the base classes compiles fine:

        sealed class Message(open val messageId: String)

        data class Track(val event: String, override val messageId: String): Message(messageId)


Ideally I would like something close to Option 2 - it allows me to combine the best of both worlds.

Otherwise, it seems my options are either handrolling my own data class functionality (copy, hashcode, equals etc) with option 1, or live with a compromise by opening up up the supertype properties with option 4.





Extending data class from a sealed class in Kotlin

I&#39;ve seen examples where a function has an argument given by ClassName.()
This doesn&#39;t seem to be an extension function, which is ClassName.Function()

An example is [Kotterknife][1]:

    private val View.viewFinder: View.(Int) -&gt; View?
        get() = { findViewById(it) }

Which I don&#39;t quite know the function of,

and [MaterialDrawerKt][2]

    fun Activity.drawer(setup: DrawerBuilderKt.() -&gt; Unit = {}): Drawer {
        val builder = DrawerBuilderKt(this)
        builder.setup()
        return builder.build()
    }

Where the code allows you to directly call 

    drawer {
        ...
    }

rather than give it arguments surrounded by the parentheses.

Is there any documentation on this anywhere?

  [1]: https://github.com/JakeWharton/kotterknife/blob/master/src/main/kotlin/kotterknife/ButterKnife.kt#L82
  [2]: https://github.com/zsmb13/MaterialDrawerKt/blob/master/library/src/main/java/co/zsmb/materialdrawerkt/builders/DrawerBuilderKt.kt#L26

Content Type	Original Author	Original Content on Stackoverflow
Question	Bjornicus	View Question on Stackoverflow
Solution 1 - Environment Variables	Patrick Boos	View Answer on Stackoverflow
Solution 2 - Environment Variables	Marcin Porwit	View Answer on Stackoverflow
Solution 3 - Environment Variables	suside	View Answer on Stackoverflow
Solution 4 - Environment Variables	LF00	View Answer on Stackoverflow

How to read an environment variable in Kotlin?

Environment Variables Problem Overview

Environment Variables Solutions

Solution 1 - Environment Variables

Solution 2 - Environment Variables

Solution 3 - Environment Variables

Solution 4 - Environment Variables

Divide by zero and no error?

Where to dispatch multiple actions in redux?

Attributions