🐚 Bash Case Statements – Use case, in, and esac for Multi-Condition Scripts

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🧲 Introduction to Bash Case Statements – Simplify Multi-Condition Checks

When a script needs to evaluate multiple possible values of a variable and perform actions accordingly, case statements offer a cleaner alternative to multiple if-elif-else blocks. The Bash case command works like a switch-case construct in other programming languages and is ideal for handling menu selections, argument parsing, and input validation.

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🎯 In this article, you’ll learn:

• How to write a case statement in Bash
• Syntax and structure of case, in, and esac
• Pattern matching in case blocks
• Practical use cases and script examples

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🧾 Basic Syntax of case Statement

case $variable in
  pattern1)
    command1
    ;;
  pattern2)
    command2
    ;;
  *)
    default_command
    ;;
esac

Keyword	Purpose
case	Begins the statement
in	Begins the list of patterns
)	Ends the pattern and starts code
;;	Ends the current block
*	Wildcard for unmatched cases
esac	Ends the statement (case in reverse)

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🧪 Example 1: Simple Menu Using case

echo "Choose an option: start | stop | status"
read action

case $action in
  start)
    echo "Starting service..."
    ;;
  stop)
    echo "Stopping service..."
    ;;
  status)
    echo "Service status: Running"
    ;;
  *)
    echo "Invalid option"
    ;;
esac

✅ Sample Run:

Choose an option: start | stop | status  
> start  
Starting service...

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🧪 Example 2: Pattern Matching with Wildcards

read -p "Enter filename: " file

case $file in
  *.txt)
    echo "Text file"
    ;;
  *.sh)
    echo "Shell script"
    ;;
  *)
    echo "Unknown file type"
    ;;
esac

✅ Output:

Enter filename: test.sh  
Shell script

💡 You can match file extensions, numbers, or wildcard patterns.

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🧪 Example 3: Case with Command-Line Arguments

case "$1" in
  start)
    echo "App started"
    ;;
  stop)
    echo "App stopped"
    ;;
  restart)
    echo "App restarted"
    ;;
  *)
    echo "Usage: $0 {start|stop|restart}"
    ;;
esac

✅ Run:

./script.sh restart

✅ Output:

App restarted

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🧠 Why Use case Instead of if-elif-else?

Feature	case	if-elif-else
Syntax readability	✅ Cleaner	❌ Verbose with many conditions
Pattern matching	✅ Built-in glob	❌ Manual with [[ ]]
Command-line parsing	✅ Ideal	✅ Possible but less elegant

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🧱 Advanced Patterns

You can use multiple matches with |:

case $input in
  y|Y|yes|YES)
    echo "You said yes."
    ;;
  n|N|no|NO)
    echo "You said no."
    ;;
  *)
    echo "Unknown input."
    ;;
esac

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📌 Summary – Bash Case Statements

The case statement in Bash is your go-to tool for handling multiple input conditions clearly and efficiently. It’s a perfect fit for user menus, argument validation, file type checks, and automation logic.

🔍 Key Takeaways:

• Use case, in, esac to check multiple input patterns
• ;; separates each case block
• * acts as a default (catch-all)
• More readable and scalable than nested if statements

⚙️ Real-world Uses:

• Parsing script parameters
• Creating interactive terminal menus
• Handling file type conditions in automation scripts

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❓ FAQ – Bash Case Statements

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❓ Can I use regex in a Bash case statement?
✅ Not full regex, but you can use glob patterns like *.txt, [0-9]*, etc.

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❓ What does ;; mean in a case statement?
✅ It ends the current condition block and prevents fall-through to the next one.

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❓ Is case faster than if in Bash?
✅ Slightly more efficient in matching many conditions and much more readable for multiple options.

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❓ Can I use variables inside patterns?
❌ Not directly. Pattern matching must use literal values or glob-style patterns, not variable substitution.

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❓ How do I add a default action in a case statement?
✅ Use *:

*)
  echo "Default case"
  ;;

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