Shell Scripting for Beginners: Common Mistakes and Solutions

If you are new to DevOps, you might find yourself diving into shell scripting, a powerful tool for automating tasks and managing your infrastructure. However, as a beginner, you may encounter some common mistakes that can hinder your progress. In this article, we will explore some of these mistakes and provide solutions to help you improve your shell scripting skills.

Mistake 1: Not Quoting Variables

One common mistake in shell scripting is not quoting variables. When you use variables without quotes, it can lead to issues with spaces and special characters. Let's take a look at an example.

#!/bin/bash
my_var=Hello World
echo $my_var

In this example, if you run the script, you will likely encounter an error because the shell will interpret "World" as a separate command.

Solution:

To avoid this issue, always quote your variables to ensure that spaces and special characters are treated as part of the variable.

#!/bin/bash
my_var="Hello World"
echo "$my_var"

By quoting the variable, you ensure that the entire string is treated as a single entity.

Mistake 2: Not Checking for Errors

Another mistake is not checking for errors in your scripts. When running commands and processes, it's crucial to handle errors appropriately to prevent unexpected behavior.

#!/bin/bash
rm -rf /some/directory

In this example, if the directory does not exist, the script will still proceed without any indication of the error.

Solution:

Always check for errors after running commands by using the $? variable, which stores the exit status of the last command.

#!/bin/bash
rm -rf /some/directory
if [ $? -ne 0 ]; then
  echo "Error: Failed to remove directory"
  exit 1
fi

By checking the exit status of the rm command, you can detect and handle errors accordingly.

Mistake 3: Using Absolute Paths

Using absolute paths in your scripts can make them less portable and more prone to errors when moving or deploying them to different environments.

#!/bin/bash
/opt/myapp/start.sh

If the script is moved to a different environment where the path is different, it will fail to execute.

Solution:

Instead of using absolute paths, it is better to use relative paths or environment variables to make your scripts more flexible and portable.

#!/bin/bash
SCRIPT_DIR=$(dirname "$(readlink -f "$0")")
$SCRIPT_DIR/start.sh

By using the dirname "$(readlink -f "$0")" command, you can retrieve the current script's directory and use it to construct the path to the start.sh script.

Mistake 4: Not Using Comments

Omitting comments in your scripts can make them difficult to understand and maintain, especially for other team members who may need to work with your code.

#!/bin/bash
# Run the process
start_process

Without proper comments, it may be unclear what the start_process function does and how it fits into the overall script.

Solution:

Always include comments to explain the purpose of your code and how it works.

#!/bin/bash
# This script starts the application process
start_process

By adding comments, you provide important context and make your script more accessible to others.

Mistake 5: Neglecting Security

Ignoring security best practices in your scripts can expose your infrastructure to vulnerabilities, especially if they involve sensitive operations or data.

#!/bin/bash
# Run a command with hard-coded credentials
some_command --username=admin --password=12345

Hard-coding credentials directly in your scripts is a significant security risk.

Solution:

Instead of hard-coding credentials, consider using environment variables or external configuration files to store sensitive information securely.

#!/bin/bash
# Run a command with credentials from environment variables
some_command --username=$USERNAME --password=$PASSWORD

By using environment variables, you can separate sensitive information from your scripts and adhere to security best practices.

To Wrap Things Up

Shell scripting is a valuable skill for DevOps professionals, but it's essential to be aware of common mistakes and best practices to write efficient, secure, and maintainable scripts. By understanding and addressing these mistakes, you can improve your shell scripting abilities and contribute to more reliable and robust automation in your infrastructure.

Remember to always quote your variables, check for errors, use relative paths, add comments, and prioritize security to ensure that your shell scripts are effective and reliable.

For further reading on best practices in shell scripting, consider exploring ShellCheck, a tool that provides static analysis for shell scripts to identify issues and improve code quality.

Now, armed with solutions to common mistakes, you can take your shell scripting skills to the next level and elevate your DevOps capabilities. Happy scripting!