This article is an UPDATE for Writing Swift Programs on Linux

This article uses Command Line Interface(CLI) to write Swift Programs. If you are new to CLI then you should read the following articles: Terminal Commands for OS X – Basic, Terminal Commands for OS X – Part 2.

This article has been written using Ubuntu version 16.04 LTS

For the best part the process is still the same.

1. Download the Swift tools for Linux from: Swift Download Page
2. Untar the downloaded files
3. Copy them to a folder of your choice. I have created a folder called “Developer” in my home folder. So I copied the untarred contents there. This is important because we will be needing the location later.
4. Switch to Terminal on your Ubuntu System.
5. First we will install clang. Run the command

   sudo apt-get install clang

6. Next we will make sure we set the PATH to the path where we copied the Swift tools. For example if the Untarred swift folder is called “swift-4.0-DEVELOPMENT-SNAPSHOT-2017-12-04-a-ubuntu16.04/usr/bin:”${PATH}” and it is in the Developer folder I created earlier then the command would be:

   export PATH=/home/admin/Developer/swift-4.0-DEVELOPMENT-SNAPSHOT-2017-12-04-a-ubuntu16.04/

   The folder name will vary from system to system. The path above is just an example.

7. Let us check to make sure that everything installed okay. We can do this with 2 commands:

   which swift

   This should show you the path to the folder.
   or

   swift --version

   This should print out the swift version.

8. Next let us test the REPL. Run the command:

   swift

   This will result in a prompt that looks like:

   Welcome to Swift version 4.0.3-dev (2dedb62a0b, Clang ab7472e733, Swift 64ab6903b2). Type :help for assistance.
    1>
   

9. Type some of the commands mentioned below:

   12 * 8
   let hello = "Welcome to Swift in Linux"
   print(hello)
   

10. Now that we know that the REPL is working well, let us move on to the next stage. Let us quit from the REPL:

    :q

Creating Single File Projects

1. Next let us use Swift Package Manager to create a single file project. I will be creating the project in the Developer folder. So I will navigate to it:cd ~/Developer/
2. Create a folder of your choice, lets call it Hello World:

   HelloWorld

3. Enter the folder:

   cd HelloWorld

4. Create a manifest file for the Package with the command:

   swift package init

   This will create some content for you. The structure should look as shown below.

5. If we run the command to build it will simply create a module for us. To do that type and run:

   swift build

6. But we would like to create an executable application. In the sources folder create a file called main.swift. You can use the command:

   touch main.swift

   to quickly create a new swift file.

7. Open the main.swift file. Write the following code in there:

   let object : HelloWorld = HelloWorld()
   print(object.text)
   print("End of program...!")
   

8. To create the executable we will first build our code:

   swift build

9. Now we will run the executable, assuming that you are still in the HelloWorld folder within the sources folder navigate to a hidden build folder. To do that first we will navigate to our main HelloWorld package folder.

   cd ../..

10. To view all the folders including the hidden folders run the list command:

    ls -la

11. Navigate to the hidden folder and the debug folder inside it to locate the executable:

    cd .build/debug/

12. To run the executable:

    ./HelloWorld

13. If you want to build and directly run & avoid doing steps 9-13 repeatedly the command is:

    swift run

Next we will see how to create multi file projects

Create Multi File Projects

1. 1. In the previous project go back to the HelloWorld folder within the Sources folder. Create a file called converter.swift:

      touch converter.swift

   2. Write the following code in that file:

      //note the code below is for demonstrating multi file projects & may not necessarily be accurate or correct
      
      //note the code below is for demonstrating multi file projects & may not necessarily be accurate or correct
      func centigrade_to_fahrenheit(temperatureInCentigrade : Float) -> Float
      {
           return ((temperatureInCentigrade*9.0/5.0)+32.0)
      }
      
      func string_to_float(input : String) -> Float
      {
           var number : Float = 0.0;
           var result : Float = 0.0
           var decimalFound : Bool = false
           var numberOfDigitsAfterDecimal : UInt8 = 0
      
           for charac in input
           {
                switch charac
                {
                     case "0":
                          number = 0.0;
                          result = (result * 10.0) + number;
                     case "1":
                          number = 1.0;
                          result = (result * 10.0) + number;
                     case "2":
                          number = 2.0;
                          result = (result * 10.0) + number;
                     case "3":
                          number = 3.0;
                          result = (result * 10.0) + number;
                     case "4":
                          number = 4.0;
                          result = (result * 10.0) + number;
                     case "5":
                          number = 5.0;
                          result = (result * 10.0) + number;
                     case "6":
                          number = 6.0;
                          result = (result * 10.0) + number;
                     case "7":
                          number = 7.0;
                          result = (result * 10.0) + number;
                     case "8":
                          number = 8.0;
                          result = (result * 10.0) + number;
                     case "9":
                          number = 9.0;
                          result = (result * 10.0) + number;
                     default:
                          decimalFound = true
                          break
                }
                if decimalFound
                {
                     numberOfDigitsAfterDecimal += 1
                }
           }
      
           for _ in 0..<numberOfDigitsAfterDecimal-1
           {
                result = result / 10.0
           }
           return result
      }

1. Write the following code in the main.swift file:

   let object : HelloWorld = HelloWorld()
   if CommandLine.arguments.count != 2
   {
           print("USAGE: centigradeToFahrenheit 33.4")
           print("You are missing an argument")
   }
   else
   {
           let temperatureInCentigrade = string_to_float(input: CommandLine.arguments[1]) 
   
           print("\(temperatureInCentigrade) is equal to \(centigrade_to_fahrenheit(temperatureInCentigrade: temperatureInCentigrade))")
   }
   print(object.text)
   print("End....!")
   

2. Build and run the code. To run it while passing arguments in:

   ./HelloWorld 33.4

So that is how you can build single file & multi file Swift applications on Linux.