Bash Scripting for Beginners: Complete Guide to Getting Started - While Loops (Part 7)

Introduction

This tutorial is designed to introduce you to the concept of while loops in Bash scripting. While loops are essential for executing a block of commands repeatedly as long as a specified condition is true. This guide will walk you through practical examples and improvements to your Bash scripts, making your scripting more efficient and powerful.

Step 1: Understanding While Loops

A while loop repeatedly executes a block of code as long as a given condition evaluates to true. The basic syntax of a while loop in Bash is:

while [ condition ]
do
    # commands to be executed
done

Practical Tips

• Ensure that the condition will eventually become false; otherwise, you will create an infinite loop.
• Use break to exit the loop prematurely when needed.

Step 2: Creating Your First While Loop

Let’s create a simple Bash script that uses a while loop. Follow these steps:

1. Open your terminal.

2. Create a new script file:

   nano my_first_while_loop.sh
   

3. Add the following code to the script:

   #!/bin/bash
   count=1
   while [ $count -le 5 ]
   do
       echo "Count is: $count"
       ((count++))
   done
   

4. Save and exit the editor (Ctrl + X, then Y, then Enter).

5. Make the script executable:

   chmod +x my_first_while_loop.sh
   

6. Run the script:

   ./my_first_while_loop.sh
   

Common Pitfalls

• Forgetting to increment the counter will result in an infinite loop.
• Using incorrect condition syntax may lead to unexpected behavior.

Step 3: Enhancing the While Loop Example

Now let's improve our while loop with user input. This will allow the script to run until the user decides to stop it.

1. Modify your script as follows:

   #!/bin/bash
   count=1
   while true
   do
       echo "Count is: $count"
       ((count++))
       read -p "Continue? (y/n): " answer
       if [ "$answer" != "y" ]; then
           break
       fi
   done
   

2. Save the changes and rerun the script.

Practical Tips

• Use the read command to take user input.
• Always check for valid input to avoid unexpected exits.

Step 4: Another Example of While Loops in the Linux Shell

You can also utilize while loops directly in the command line. For instance, to continuously display a message until a certain condition is met, use:

count=1
while [ $count -le 5 ]; do
  echo "Hello World"
  ((count++))
done

Conclusion

In this tutorial, you learned about while loops in Bash scripting, including their syntax, common uses, and how to enhance scripts with user input. Experiment with different conditions and commands in your scripts to deepen your understanding. As a next step, explore additional Bash scripting concepts such as for loops and functions to expand your scripting capabilities. Happy scripting!