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Using Shell Script if else: Detailed Guide with Examples

When writing a shell script, not every command needs to run all the time.
The if-else structure gives decision making ability to your scripts.

In this guide, you will learn Bash if, else and elif structures with real scenarios.

What Will You Learn in This Guide?​

  • basic if-else syntax
  • Numerical and textual comparisons
  • File and permission checks
  • use of elif and nested if
  • Automation scenarios

Technical Summary​

This guide explains how to use Shell Script if else on Linux and Ubuntu systems.
The goal is to run automation scripts based on conditions.

Basic Logic of the if-else Structure​

The basic structure in Bash is as follows:

if [ koşul ]; then
  komutlar_1
else
  komutlar_2
fi
  • This construct runs different code if the condition is true or false.

⚠️ Note:​

  • space inside is mandatory. Bash is case sensitive.

  • Most Frequently Used Condition Operators

ConditionDescription
[ $a -eq $b ]Are the numbers equal
[ $a -gt $b ]Is a greater than b
[ $a -lt $b ]Is a less than b
[ -f dosya ]Is there a file
[ -r dosya ]Is the file readable
[ -z "$var" ]Is the variable empty

1. Comparing Two Numbers​


#!/bin/bash
m=10
n=20

if [ $n -eq $m ]; then
  echo "Sayılar eşit"
else
  echo "Sayılar farklı"
fi
  • This script checks numerical equality.

2. File and Read Permission Control (Nested if)​


#!/bin/bash
dosya="/home/genixnode/ayarlar.conf"

if [ -f "$dosya" ]; then
  if [ -r "$dosya" ]; then
    echo "Dosya mevcut ve okunabilir"
  else
    echo "Dosya var ama okuma izni yok"
  fi
else
  echo "Dosya bulunamadı"
fi
  • This structure is frequently used in security and configuration controls.

3. Using elif for Multiple Conditions​


#!/bin/bash
puan=85

if [ $puan -ge 90 ]; then
  echo "Derece: A"
elif [ $puan -ge 80 ]; then
  echo "Derece: B"
else
  echo "Derece: C veya altı"
fi
  • elif simplifies code in multiple decision scenarios.

Frequently Asked Questions (FAQ)​

1. What is the difference between == and -eq? == makes a text comparison, -eq makes a numerical comparison.

2. Why are square brackets important? [ is a command. If there is no space, it gives an error.

3. How to write multiple conditions? && (and), || (or) operators are used.

4. What can I use instead of if? The case structure is recommended in cases with multiple options.

Result​

if-else is the basic building block of Shell Script. When used correctly, automation works safer and smarter.

You can speed up your processes by using these scripts on your GenixNode servers 🚀