Master Shell Scripting: A Practical Guide to if else Statements

Unlock the power of conditional logic in your shell scripts. This guide provides clear examples of using if else statements to control the flow of your scripts. Make your scripts smarter and more efficient!

Why Use if else in Shell Scripts?

Conditional programming is key to creating dynamic and responsive shell scripts. if else statements let you execute specific code blocks based on whether a condition evaluates to true or false. This enables your scripts to make decisions and adapt to different situations.

Understanding the Basics of if else

The if else statement is a fundamental building block in shell scripting. Let's break down its structure:

if [ condition ]
then
  # Code to execute if the condition is true
else
  # Code to execute if the condition is false
fi

• if: Initiates the conditional statement, followed by the condition to evaluate.
• then: Indicates what to do if the condition is true.
• else: Specifies the alternative action if the condition is false.
• fi: Marks the end of the if else block.

Shell scripting is case-sensitive. Always use lowercase for keywords like if, then, else, and fi.

Real-World if else Examples in Shell Scripting

Let's dive into practical examples that demonstrate the versatility of if else statements.

1. Check for Number Equality with -eq

#!/bin/bash
num1=10
num2=20

if [ $num1 -eq $num2 ]
then
  echo "Numbers are equal"
else
  echo "Numbers are not equal"
fi

Explanation: This script compares two numbers using the -eq operator (equal). The output will indicate whether the numbers are equal or not. Perfect for configuration checks!

2. Comparing Numerical Values: -gt, -lt, -ge, -le

#!/bin/bash
val1=5
val2=8

if [ $val1 -gt $val2 ]
then
  echo "$val1 is greater than $val2"
else
  echo "$val2 is greater than or equal to $val1"
fi

Explanation: This example uses -gt (greater than) to determine which variable holds the larger value and demonstrates how shell script if else constructs handle comparison.

3. Determine Even or Odd with Modulo Operator

#!/bin/bash
number=7
if [ $((number % 2)) -eq 0 ]
then
  echo "$number is an even number"
else
  echo "$number is an odd number"
fi

Explanation: This script uses the modulus operator (%) to check if a number is even or odd. The double parentheses ((...)) are used for arithmetic evaluation.

4. Create a Password Prompt Script

#!/bin/bash
read -p "Enter password: " password
if [ "$password" = "secret" ]
then
  echo "Access granted!"
else
  echo "Incorrect password. Access denied."
fi

Explanation: This creates a simple password prompt. It reads user input and compares it with a predefined password. Note the use of quotes around $password for safety.

Key Takeaway: This example showcases how to develop a simple password check tool.

Essential Operators for Shell Script if else Statements

Conclusion: Mastering Conditional Logic

if else statements are indispensable. Mastering shell script if else statements will significantly improve your scripting capabilities. Use these conditional tools to create smarter and more adaptable shell scripts!