Bash Case: How To Run Multiple Blocks On A Match?

Aug 15, 2025 by Elias Adebayo 50 views

Can You Execute Multiple Case Blocks in Bash? Exploring Alternatives

Hey there, scripting enthusiasts! Ever found yourself wondering if you can execute multiple blocks within a Bash case statement when a pattern matches? It's a common question, especially when you're trying to streamline your scripts and avoid repetitive code. Let's dive into this topic and explore some cool alternatives.

Understanding the Basics of Bash `case` Statements

Before we get into the nitty-gritty, let's quickly recap what a case statement is and how it works in Bash. Think of it as a more powerful version of a series of if-elif-else statements. It allows you to compare a variable against multiple patterns and execute the corresponding code block.

The basic syntax looks like this:

case $variable in
  pattern1) # Code to execute if $variable matches pattern1 ;;
  pattern2) # Code to execute if $variable matches pattern2 ;;
  pattern3) # Code to execute if $variable matches pattern3 ;;
  *) # Default code to execute if no pattern matches ;;
esac

The Magic Behind the case Statement

In a case statement, Bash evaluates the variable and checks it against each pattern sequentially. When a match is found, the corresponding code block is executed. Here's the crucial part: after executing the code block, the case statement terminates. This is why, by default, you can only execute one block per case statement.

The ;; (double semicolon) plays a vital role here. It acts as a terminator, signaling the end of a code block and preventing further pattern matching within the case statement. Without it, execution would fall through to the next block, which is usually not the desired behavior.

The Challenge: Executing Multiple Blocks

Now, let's address the million-dollar question: can you execute multiple blocks when a pattern matches? The straightforward answer, given the default behavior of case, is no. Once a match is found and the code block is executed, the case statement exits. But, fear not! There are clever workarounds to achieve a similar effect without resorting to multiple case statements or if conditions.

Digging Deeper: Why Limit to One Block?

You might wonder, "Why does Bash limit us to one block execution?" Well, it's designed that way to ensure clarity and avoid ambiguity. Imagine if multiple blocks executed for a single match – it could lead to unexpected behavior and make your scripts harder to debug. The single-execution model makes the logic flow predictable and easier to follow. However, this doesn't mean we're stuck. We can use Bash's features to bend the rules a little.

Workaround 1: Grouping Commands within a Block

The simplest and most common approach is to group multiple commands within a single code block. Instead of trying to execute separate blocks, you can put all the desired actions within one block, separated by semicolons or newlines. This way, you effectively achieve the execution of multiple operations for a single pattern match.

case $variable in
  pattern1) 
    command1; 
    command2; 
    command3 ;;
  pattern2) 
    command4
    command5
    command6 ;;
  *) 
    echo "No match found" ;;
esac

In this example, if $variable matches pattern1, command1, command2, and command3 will all be executed. Similarly, for pattern2, command4, command5, and command6 will run. This method keeps your case statement clean and readable while allowing you to perform multiple actions.

Practical Example: File Handling

Let's say you want to perform several actions based on a file type. You can easily group commands like this:

file_extension="${filename##*.}" # Extract file extension

case $file_extension in
  txt) 
    echo "Text file detected"; 
    less "$filename"; 
    wc -l "$filename" ;;
  pdf) 
    echo "PDF file detected"; 
    pdfinfo "$filename"; 
    pdftotext "$filename" - ;;
  *) 
    echo "Unknown file type" ;;
esac

Here, if the file is a .txt, we print a message, view it with less, and count the lines. If it's a .pdf, we get PDF info and convert it to text. All within a single, clean case block.

Workaround 2: Using Functions

Another elegant solution is to define functions for each set of actions and then call those functions within the case blocks. This approach enhances code reusability and makes your case statement more organized, especially when dealing with complex logic. Functions allow you to encapsulate a series of commands and give them a meaningful name, making your script easier to read and maintain.

function handle_pattern1() {
  echo "Handling pattern 1";
  command1;
  command2;
}

function handle_pattern2() {
  echo "Handling pattern 2";
  command3;
  command4;
}

case $variable in
  pattern1) handle_pattern1 ;;
  pattern2) handle_pattern2 ;;
  *) echo "No match found" ;;
esac

In this setup, handle_pattern1 and handle_pattern2 are functions that contain the commands to be executed for their respective patterns. The case statement simply calls the appropriate function. This method keeps the case statement concise and moves the detailed logic into separate, manageable functions.

Real-World Scenario: Menu-Driven Scripts

Functions shine when creating menu-driven scripts. Imagine a script that presents a menu of options to the user. Each option can correspond to a function:

function option1() {
  echo "Executing Option 1";
  # ... more commands ...
}

function option2() {
  echo "Executing Option 2";
  # ... more commands ...
}

function option3() {
  echo "Executing Option 3";
  # ... more commands ...
}

read -p "Choose an option (1, 2, or 3): " choice

case $choice in
  1) option1 ;;
  2) option2 ;;
  3) option3 ;;
  *) echo "Invalid option" ;;
esac

This structure makes your script incredibly modular and easy to extend. Adding a new option is as simple as defining a new function and adding a case to the case statement.

Workaround 3: Using `eval` (Use with Caution!)

For advanced scenarios, you might consider using the eval command. eval takes a string as input and executes it as a Bash command. This can be used to dynamically construct and execute command sequences within a case block. However, this method should be used with extreme caution, as it can introduce security vulnerabilities if not handled properly. Always sanitize your inputs when using eval to prevent command injection attacks.

case $variable in
  pattern1) 
    commands="echo \"Handling pattern 1\"; command1; command2";
    eval "$commands" ;;
  pattern2) 
    commands="echo \"Handling pattern 2\"; command3; command4";
    eval "$commands" ;;
  *) 
    echo "No match found" ;;
esac

In this example, the commands are stored as a string in the commands variable, and then eval is used to execute that string. While this provides flexibility, it also opens the door to potential risks if the input is not carefully controlled.

Security Implications of `eval`

Imagine if the $variable in the previous example was influenced by user input. A malicious user could inject commands into the commands string, leading to arbitrary code execution. For instance, if $variable somehow led to commands becoming `echo