Scala is an object-oriented and functional programming language. It a popular language that has been used for developing applications, such as Spark, Akka, and Lift.
In this article, I will show you how to install Scala on a CentOS 7 server instance.
All of the instructions in this article are applicable to a non-root sudo user using CentOS 7. Thus, you need to deploy a fresh Vultr CentOS 7 server instance and create a non-root sudo user before diving in.
After logging in as the non-root sudo user from your SSH terminal, the first thing you need to do is to update the system:
sudo yum update -y && sudo reboot
Use the same user to log in again after the system reboots.
Scala requires the Java runtime version 1.6 or later. Here, you can install the latest version of OpenJDK Runtime Environment 1.8.0 using YUM:
sudo yum install java-1.8.0-openjdk.x86_64
You can validate the installation of Java runtime by running the following command:
java -version
This command should output something that resembles:
openjdk version "1.8.0_91"
OpenJDK Runtime Environment (build 1.8.0_91-b14)
OpenJDK 64-Bit Server VM (build 25.91-b14, mixed mode)
Besides, you need to set the "JAVA_HOME" and "JRE_HOME" environment variables.
sudo cp /etc/profile /etc/profile_backup #Backup the profile file in order to prevent unintentional mistakes
echo 'export JAVA_HOME=/usr/lib/jvm/jre-1.8.0-openjdk' | sudo tee -a /etc/profile
echo 'export JRE_HOME=/usr/lib/jvm/jre' | sudo tee -a /etc/profile
source /etc/profile
Now, you can print the two environment variables for review:
echo $JAVA_HOME
echo $JRE_HOME
Download and install the latest Scala RPM file from the Scala official website, which at the time of writing is 2.11.8:
cd ~
wget http://downloads.lightbend.com/scala/2.11.8/scala-2.11.8.rpm
sudo yum install scala-2.11.8.rpm
Verify your installation:
scala -version
The output should resemble:
Scala code runner version 2.11.8 -- Copyright 2002-2016, LAMP/EPFL
The Scala installation is complete. Let's have a look at how to use it.
Run the Scala code runner and get into the Scala shell:
scala
In the Scala shell, you can calculate the result of a formula:
scala> 1+2
res0: Int = 3
or, execute a function:
scala> println("Hello Scala")
Hello Scala
If you want to quit the Scala shell:
:q
You can also use the scalac program to compile .scala source code.
Write the source code of an example program using vi:
vi hello.scala
Input the code segment below:
object HelloWorld {
def main(args: Array[String]) {
println("Hello World!")
}
}
Save and quit:
:wq
Compile the source code with scalac:
scalac hello.scala
The program will output two compiled files: HelloWorld.class and HelloWorld$.class. You can run the compiled file with scala:
scala HelloWorld
The output will read:
Hello World!
Moreover, you can embed Scala functions into a bash script, and then run the script using bash:
vi script.sh
Populate the file with:
#!/bin/sh
exec scala "$0" "$@"
!#
object HelloWorld extends App {
println("Hello world!")
}
HelloWorld.main(args)
Save and quit:
:wq
Run the script in the bash shell:
sh script.sh
Again, the output will read:
Hello world!