Forem: Alan

What command do you 'has' ? | Strange CLI Apps

Alan — Tue, 13 Dec 2022 14:00:24 +0000

`has`: ✅ checks presence of command line tools

AIM: checks presence of various command line tools on the PATH and reports their installed version.
Usage for Unix System

Reference

For more usage and installation instructions, visit official repo: https://github.com/kdabir/has

One more command: `which`

Difference: Compared has, which is not being updated for 4 years. which is pre-installed in each Unix System and being maintained.
AIM: which also checks presence of various command line tools on the PATH
Usage for Unix System

Please follow this series for more Strange CLI Apps example!

Is 'fuck' really a Unix command ? | Strange CLI Apps

Alan — Tue, 13 Dec 2022 09:24:21 +0000

Is `fuck` really a command?

fuck is actually a command.
AIM: It is aim to correct miss-spelling command that user execute.
Usage in Ubuntu shown below

Reference

For more usage and installation instructions, visit official repo: https://github.com/nvbn/thefuck

Strange CLI Apps Series Intro

Background: I am often surprised on Unix 3rd party commands for its fun and high productivity gain.
Aim: This series can be a platform to share some beautiful or productive linux command snippets.

Please follow this series for more Strange CLI Apps example!

Java by Example: If/Else

Alan — Mon, 12 Dec 2022 07:38:07 +0000

Condition branching with if and else in Java is straight-forward.

class Conditions {
  public static void main(String[] args) {

    // Here’s a basic example.
    if(7%2 == 0){
        System.out.println("7 is even");
    } else {
        System.out.println("7 is odd");
    }

    // You can have an if statement without an else.
    if(8%4 == 0){
        System.out.println("8 is divisible by 4");
    }

    // Here is an if-else-if branching example
    Integer num = 9;
    if( num < 0){
        System.out.println(num, "is negative");
    } else if(num < 10){
        System.out.println(num, "has 1 digit");
    } else {
        System.out.println(num, "has multiple digits");
    }

    // This is Ternary Operator; 
    // It enable testing a condition in single-line,
    // replacing the multi-line if-else tomaking the code compact.
    final String msg = num > 10 
      ? "9 is greater than 10" 
      : "9 is less than or equal to 10";
    System.out.println(msg);
  }
}

javac Condition.java
java Condition
# 7 is odd
# 8 is divisible by 4
# 9 has 1 digit
# 9 is less than or equal to 10

Java By Example: Loop(for and while)

Alan — Mon, 12 Dec 2022 06:55:17 +0000

for and while are the two Java looping construct. Here are some basic types of for and while loops.

class Loop {
  public static void main(String[] args) {

    // The most basic type, with a single condition.
    Integer i = 1;
    while(i <= 3){
        System.out.println(i);
    i = i + 1;
    }

    // A classic initial/condition/after `for` loop.
    for(Integer j = 7; j <= 9; j++){
         System.out.println(j);
    }

    // `while(true)` will loop repeatedly
    // until you `break` out of the loop
    // or `return` from the enclosing function.
    while(true){
        System.out.println("loop");
    break;
    }

    // You can also `continue` to the next iteration of the loop.
    for(Integer n = 0; n <= 5; n++) {
        if(n%2 == 0){
            continue;
        }
        System.out.println(n);
    }

  }

}

javac Loop.java
java Loop
# 1
# 2
# 3
# 7
# 8
# 9
# loop
# 1
# 3
# 5

We’ll see some other for forms later when we look at:
foreach statements (Foreach),
async channels (Async), and other data structures.

Java By Example: Constants

Alan — Mon, 12 Dec 2022 06:29:15 +0000

Java supports constants of character, string, boolean, and numeric values.

import java.lang.Math;
import java.math.BigDecimal;

class Main {
  public static void main(String[] args) {

    // 'final' declares a constant value.
    final String s = "constant";
    System.out.println(s);

    // A `final` statement can appear before Data Type.
    final Integer n = 500000000;

    // A numeric constant has type usually declared by user.
    final Double d = 3e+20 / n;
    System.out.println(d);

    // To convert a numeric constant type
    // It is required to cast to `BigDecimal` first
    // Then cast to other data types (like `BigInteger`)
    final BigDecimal e = new BigDecimal(d);
    System.out.println(e.toBigInteger());

    System.out.println(Math.sin(d));
  }
}

javac Constants.java
java Constants
# constant
# 6e+11
# 600000000000
# -0.28470407323754404

Reference:
BigDecimal Class in Java - GeeksforGeeks
is there anyway to convert from Double to BigInteger? – Java (tutorialink.com)

Java By Example: Variables

Alan — Mon, 12 Dec 2022 06:25:30 +0000

In Java, variables are explicitly declared and used by the compiler to e.g. check type-correctness of function calls.

class Variables {
  public static void main(String[] args) {

    //You can declares 1 or more variables.
    String a = "initial";
    System.out.println(a);

    // You can declare multiple variables at once.
    Integer b = 1, c = 2;
    System.out.println(b + " " + c);

    //'var' will infer the type of initialized variables.
    var d = true;
    System.out.println(d);

    // Variables declared without a corresponding initialization are not able to be called, calling will be resulting in error.
    // Integer e;
    // System.out.println(e);
  }
}

javac Variables.java
java Variables
# initial
# 1 2
# true

Java By Example: Values

Alan — Mon, 12 Dec 2022 06:09:27 +0000

Java has various value types including String , Integer, Double, Boolean, etc. Here are a few basic examples.

The usage of these data types are shown in the below code block

class Values {
  public static void main(String[] args) {

    // Strings, that can be added together with +.
    System.out.println("Java" + " " + "Lang"); 

    // Integer and Double
    Integer sum = 1+1;
    Double division = 7.0/3.0;
    System.out.println("1+1 = " + sum);
    System.out.println("7.0/3.0 =" + division);

    //Booleans, with boolean operators as you’d expect.
    System.out.println(true && false);
    System.out.println(true || false); 
    System.out.println(!true);
  }
}

Below are the commands and output.

javac Values.java
java Values
# Java Lang
# 1+1 = 2
# 7.0/3.0 = 2.3333333333333335
# false
# true
# false

Java By Example: Hello World

Alan — Mon, 12 Dec 2022 06:06:35 +0000

Our first program will print the classic “hello world” message. Here’s the full source code.

class Helloworld {
  public static void main(String[] args) {
    System.out.println("Hello world!");
  }
}

To run the program, we need to build our programs into Byte Code.
We can do this using javac Helloworld.java.
We can then execute the built java .class file directly.

javac Helloworld.java
ls
# Helloworld.java Helloworld.class

java Helloworld
# Hello world!

Java By Example

Alan — Mon, 12 Dec 2022 06:03:59 +0000

TLDR: Check out the Java examples shown in the above series

What is Java

Java is an open source programming language designed for building well-architectured, multithread, and reliable software.

Java by Example is a hands-on introduction to Java using annotated example programs. Check out the first example(Hello World) or browse the full list above.

Target Audience

It is a Java beginner tutorial demonstrating the syntax of Java.
It aims for the audience who already know another programming language (for example JS, Python, C++) and want to learn Java fast.

NodeJS virtual environment in Fedora Toolbox

Alan — Sat, 10 Dec 2022 06:08:15 +0000

Fedora Toolbox is used to create isolated development environment with container technologies(podman).

Why Fedora Toolbox
1.It is tailor made and built-in fedora.
2.By utilizing a Fedora base image, it can install cross language and dependencies environment.
3.As Toolbox is mutable environment and docker environment is immutable; Docker is usually for software deployment and this is for software development

Hands-on Example

So let's start with creating nodeJS development environment inside Fedora.

toolbox create node
toolbox enter node
sudo dnf install nodejs

# Install Yarn
curl --silent --location https://dl.yarnpkg.com/rpm/yarn.repo | sudo tee /etc/yum.repos.d/yarn.repo
sudo dnf install yarn

Output for Fedora Toolbox

Create a fedora container, named node

Created Container: Node
# ... Other logs downloading and setting up container

Entering virtual environment

Manage Environemnts | Containers

List Containers

toolbox list

Remove Containers

toolbox rm node
# No Output for this Command

Reference

To understand the container technology behind Fedora toolbox, you can visit this essay

Forem: Alan

What command do you 'has' ? | Strange CLI Apps

has: ✅ checks presence of command line tools

Reference

One more command: which

Is 'fuck' really a Unix command ? | Strange CLI Apps

Is fuck really a command?

Reference

Strange CLI Apps Series Intro

Java by Example: If/Else

Java By Example: Loop(for and while)

Java By Example: Constants

Java By Example: Variables

Java By Example: Values

Java By Example: Hello World

Java By Example

What is Java

Target Audience

NodeJS virtual environment in Fedora Toolbox

Hands-on Example

Manage Environemnts | Containers

Reference

`has`: ✅ checks presence of command line tools

One more command: `which`

Is `fuck` really a command?