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Linux Command Line Mastery · Pelajaran

Pernyataan Kondisional: `if`, `else`, `case`

Terapkan logika pengambilan keputusan dalam skrip Anda menggunakan berbagai konstruksi kondisional.

Pernyataan Kondisional: `if`, `else`, `case` adalah pelajaran Linux Command Line Mastery gratis di CoddyKit. Ini adalah pelajaran 2 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Linux Command Line Mastery, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Linux Command Line Mastery mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

Making Decisions in Scripts

In shell scripting, just like in life, you often need to make decisions. Conditional statements allow your scripts to execute different commands based on whether a certain condition is true or false.

This is crucial for creating flexible and powerful scripts that can adapt to different situations or user inputs.

The Basic `if` Statement

The simplest conditional is the if statement. It checks a condition, and if that condition is true, it executes a block of commands. If false, it skips them.

The basic syntax looks like this:

  • if [ condition ]; then
  • # commands to run if true
  • fi

Remember fi to close the if block!

Simple `if` Example

Let's see a simple if statement in action. This script checks if a variable num is greater than 5.

Try changing the value of num to see how the output changes!

#!/bin/bash

num=7

if [ "$num" -gt 5 ]; then
  echo "Number is greater than 5."
fi

num=3

if [ "$num" -gt 5 ]; then
  echo "Number is greater than 5. (This won't print)"
fi

`if-else`: Two Paths

What if you want to execute one set of commands if a condition is true, and a different set if it's false? That's where else comes in.

The if-else statement provides two distinct paths for your script:

  • if [ condition ]; then
  • # commands if condition is true
  • else
  • # commands if condition is false
  • fi

Using `if-else`

This script uses if-else to determine if a number is even or odd. We use the arithmetic evaluation (( )) for clearer number comparisons and calculations.

The % operator gives the remainder of a division. If num % 2 is 0, it's even!

#!/bin/bash

num=4

if (( num % 2 == 0 )); then
  echo "$num is an even number."
else
  echo "$num is an odd number."
fi

num=9

if (( num % 2 == 0 )); then
  echo "$num is an even number. (This won't print)"
else
  echo "$num is an odd number."
fi

`elif`: Multiple Conditions

Sometimes you have more than two possible outcomes. For these situations, you can use elif (short for "else if") to check multiple conditions sequentially.

The script checks conditions one by one. The first one that's true gets its commands executed, and the rest are skipped.

  • if [ cond1 ]; then ...
  • elif [ cond2 ]; then ...
  • else ...
  • fi

Chain of `elif`

Here's an example using if-elif-else to assign a letter grade based on a score. Notice how the conditions are checked from highest to lowest score.

If a score is 95, the first if condition (>= 90) is met, and it prints "A". The other elif and else blocks are then ignored.

#!/bin/bash

score=85

if [ "$score" -ge 90 ]; then
  echo "Grade: A"
elif [ "$score" -ge 80 ]; then
  echo "Grade: B"
elif [ "$score" -ge 70 ]; then
  echo "Grade: C"
else
  echo "Grade: F"
fi

`case`: Simple Selection

When you have a single variable or expression that can have many possible values, and you want to perform different actions for each value, the case statement is often cleaner than a long if-elif-else chain.

It's great for menu-driven scripts or handling specific input options.

  • case $variable in
  • pattern1) commands ;;
  • pattern2) commands ;;
  • *) default commands ;;
  • esac

Using `case` Statements

This script demonstrates how to use case to respond to different user actions (start, stop, restart). The *) pattern acts as a default, catching any unmatched values.

Each block of commands ends with ;;, which is crucial for the case statement to work correctly.

#!/bin/bash

action="start"

case "$action" in
  "start")
    echo "Starting service..."
    ;;
  "stop")
    echo "Stopping service..."
    ;;
  "restart")
    echo "Restarting service..."
    ;;
  *) # Default case for anything else
    echo "Invalid action: $action"
    ;;
esac

action="status"

case "$action" in
  "start") echo "Starting service..." ;;
  "stop") echo "Stopping service..." ;;
  "restart") echo "Restarting service..." ;;
  *) echo "Invalid action: $action" ;;

esac

Conditional Challenge

Read the script below carefully. What will be the output when this script is run?

#!/bin/bash

color="blue"

if [ "$color" == "red" ]; then
  echo "It's a primary color."
elif [ "$color" == "yellow" ]; then
  echo "It's another primary color."
elif [ "$color" == "blue" ]; then
  echo "Yes, blue is primary!"
else
  echo "Unknown color."
fi

Decisions Made Easy

Great job! You've learned the fundamental ways to add decision-making logic to your shell scripts.

  • if: Executes commands if a condition is true.
  • if-else: Provides two paths, one for true and one for false.
  • elif: Allows chaining multiple conditions for more complex logic.
  • case: A clean way to handle multiple choices based on a single value.

These constructs are essential for writing scripts that can respond dynamically to different inputs and situations.

Pertanyaan yang Sering Diajukan

Apakah pelajaran “Pernyataan Kondisional: `if`, `else`, `case`” gratis?

Ya — teks lengkap “Pernyataan Kondisional: `if`, `else`, `case`” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Linux Command Line Mastery, upgrade ke CoddyKit PRO. Kursus Linux Command Line Mastery mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Pernyataan Kondisional: `if`, `else`, `case`”?

Terapkan logika pengambilan keputusan dalam skrip Anda menggunakan berbagai konstruksi kondisional. Kamu berlatih Linux Command Line Mastery dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

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Semua pelajaran dalam kursus ini

  1. Variabel, Masukan, dan Keluaran
  2. Pernyataan Kondisional: `if`, `else`, `case`
  3. Perulangan: `for`, `while`, `until`
  4. Fungsi dan Argumen dalam Skrip Shell
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