Bash Script Goto Label Example: How to Simulate Label-Based Navigation

Prerequisites

• Basic understanding of Bash scripting
• Knowledge of case statements
• Familiarity with loops (e.g., while)
• A Linux or macOS environment with Bash installed

The Script

This script simulates a goto-like behavior using a variable to track the current “label” and a case statement to jump between sections.

#!/bin/bash

label="start"

while true; do
    case $label in
        start)
            echo "This is the start label."
            echo "Where do you want to go? (next/end)"
            read -r choice
            if [[ $choice == "next" ]]; then
                label="next"
            elif [[ $choice == "end" ]]; then
                label="end"
            else
                echo "Invalid choice. Staying at start."
            fi
            ;;
        next)
            echo "You are now at the next label."
            echo "Where to now? (start/end)"
            read -r choice
            if [[ $choice == "start" ]]; then
                label="start"
            elif [[ $choice == "end" ]]; then
                label="end"
            else
                echo "Invalid choice. Staying at next."
            fi
            ;;
        end)
            echo "You have reached the end. Exiting..."
            break
            ;;
        *)
            echo "Unknown label. Exiting..."
            break
            ;;
    esac
done

Step-by-Step Explanation

Here’s how the script works, broken down step-by-step:

1. Initialize the Label: Set the initial label to “start” using a variable.
2. Create a Loop: Use a while true loop to allow repeated execution of the case statement.
3. Define Case Labels: Create branches in the case statement for each label (e.g., start, next, end).
4. Handle User Input: Use read to capture user input and update the label variable accordingly.
5. Exit Gracefully: Break the loop when the label is “end” or invalid.

How to Run the Script

Follow these steps to execute the script:

1. Save the script to a file, e.g., goto_example.sh.
2. Make the script executable by running chmod +x goto_example.sh.
3. Run the script using ./goto_example.sh.

Conclusion

Simulating goto in Bash using structured techniques like case statements provides a cleaner and more maintainable way to control script flow. This approach is versatile and avoids the common pitfalls of traditional goto logic.

FAQ

1. Why doesn’t Bash support goto natively?

   Bash promotes structured programming, which is easier to read, debug, and maintain compared to unstructured goto logic.

2. Can I use this technique in other shells?

   Yes, this approach can be adapted for other shells like Zsh, as long as they support case statements and loops.

3. What happens if an invalid label is entered?

   The script will display an error message and exit gracefully.

4. Can this approach handle complex scripts?

   Yes, this technique is scalable and can handle complex flow control with multiple labels.

Troubleshooting

• Error: Permission denied
  Fix: Ensure the script is executable by running chmod +x filename.sh.
• Error: Command not found
  Fix: Verify that Bash is installed and the script is being executed with the correct path.