Shell Scripting Tutorial for Beginners 2 - using Variables and Comments

Introduction

This tutorial will guide you through the basics of shell scripting, focusing on variables and comments in Linux. Understanding these concepts is crucial for automating tasks and creating powerful scripts. By the end of this guide, you will know how to define and use both system and user-defined variables, as well as how to comment your code effectively.

Step 1: Understanding Variable Types

In shell scripting, there are two main types of variables:

• System Variables:

  • Created and maintained by Linux.
  • Defined in capital letters (e.g., PATH, HOME).

• User Defined Variables (UDV):

  • Created and maintained by the user.
  • Defined in lowercase letters (e.g., myvar, count).

Practical Tip

When naming your variables, ensure they start with an alphabetic character and may include alphanumeric characters or underscores.

Step 2: Creating User Defined Variables

To create a user-defined variable, use the following syntax:

var_name=value

For example, to set a variable t to the value 100:

t=100

Accessing Variable Values

To access the value of a variable, precede the variable name with a dollar sign ($):

echo "$t"

This command will print 100.

Step 3: Setting and Printing Variable Values

To print a formatted string that includes a variable, use the following syntax:

echo "\$t = $t"

This will output:

$t = 100

Common Pitfall

Remember to use double quotes around the variable when printing it in order to prevent unwanted interpretation of special characters.

Step 4: Removing Variables

To remove a variable from the environment, use the unset command:

unset var_name

For example, to remove the variable t, use:

unset t

Practical Advice

Use unset with caution, as it will permanently remove the variable and its value.

Step 5: Adding Comments

Comments are essential for enhancing the readability of your scripts. In shell scripting, comments start with the # symbol. Anything following this symbol on that line will be ignored by the interpreter.

Example of Commenting

# This is a user-defined variable
t=100  # Setting the variable t to 100

Conclusion

In this tutorial, you learned about the different types of variables in shell scripting, how to create and manipulate user-defined variables, and the importance of comments for code clarity. As you continue to explore shell scripting, practice creating scripts that utilize these concepts to automate tasks effectively. Consider diving deeper into advanced scripting techniques or exploring other programming languages to expand your skill set.