Variable Declaration and Assignment

In programming, a variable serves as a placeholder for an unknown value, enabling the user to store the different data and access them whenever needed. During compilation or interpretation, the symbolic names of variables are replaced with their corresponding data locations. This article will mainly focus on the variable declaration and assignment in a Bash Script. So, let’s start.

Key Takeaways

• Getting familiar with Bash Variables.
• Learning to declare and assign variables.

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Factors of Variable Declaration and Assignment

There are multiple factors to be followed to declare a variable and assign data to it. Here I have listed the factors below to understand the process. Check it out.

1. Choosing Appropriate Variable Name

When choosing appropriate variable names for declaration and assignment, it’s essential to follow some guidelines to ensure clarity and readability and to avoid conflicts with other system variables. Here some common guidelines to be followed are listed below:

• Using descriptive names: Using descriptive names in variable naming conventions involves choosing meaningful and expressive names for variables in your code. This practice improves code readability and makes it easier to grasp the purpose of the code at a glance.
• Using lowercase letters: It is a good practice to begin variable names with a lowercase letter. This convention is not enforced by the bash language itself, but it is a widely followed practice to improve code readability and maintain consistency. For example name, age, count, etc.
• Separating words with underscores: Using underscores to separate words in variable names enhances code readability. For example first_name, num_students, etc.
• Avoid starting with numbers: Variable names should not begin with a number. For instance, 1var is not a valid variable
• Avoiding special characters: Avoid using special characters, whitespace, or punctuation marks, as they can cause syntax errors or introduce unexpected behavior. For instance, using any special character such as @, $, or # anywhere while declaring a variable is not legal.

2. Declaring the Variable in the Bash Script

In Bash, declaring variables and assigning values to them can be done for different data types by using different options along with the declare command. However, you can also declare and assign the variable value without explicitly specifying the type.

3. Assigning the Value to the Variable

When declaring variables for numeric values, simply assign the desired number directly, as in age=30 for an integer or price=12.99 for a floating–point value. For strings, enclose the text in single or double quotes, such as name=’John‘ or city=”New York“. Booleans can be represented using 0 and 1, where 0 indicates false and 1 represents true, like is_valid=1.

Arrays are declared by assigning a sequence of values enclosed in parentheses to a variable, e.g., fruits=(“apple” “banana” “orange”). To create associative arrays (key-value pairs), use the declare -A command followed by assigning the elements, like declare -A ages=([“John”]=30 [“Jane”]=25).

4 Practical Cases of Declaring and Assigning Bash Variable

In this section, I have demonstrated some sample Bash scripts that will help you understand the basic concept of variable declaration and assignment in Bash script. So let’s get into it.

Case 01: Basic Variable Assignment in Bash Script

In my first case, I have shown a basic variable assignment with its output. Here, I have taken a string and an integer variable to show the basic variable assignment mechanism. Follow the given steps to accomplish the task.

Steps to Follow >

❶ At first, launch an Ubuntu terminal.

❷ Write the following command to open a file in Nano:

nano basic_var.sh

❸ Copy the script mentioned below:

#!/bin/bash
# Variable Declaration and Assignment
name="John"
age=30

# Printing the variables
echo "Name: $name"
echo "Age: $age"

❹ Press CTRL+O and ENTER to save the file; CTRL+X to exit.

❺ Use the following command to make the file executable:

chmod u+x basic_var.sh

❻ Run the script by the following command:

./basic_var.sh

Upon executing the script, the output displays the content of the variables: Name: John and Age: 30.

Case 02: Input From User and Variable Assignment

In Bash, you can take input from the user and store it in variables using the read command. To do so use the following script:

Script (user_var.sh) >

#!/bin/bash
# Prompt the user for input
read -p "Enter your name: " name
read -p "Enter your age: " age

# Printing the variables
echo "Name: $name"
echo "Age: $age"

Now, run the following command into your terminal to execute the bash file.

./user_var.sh

When you run the script, it will ask you to enter your name and age. Upon providing the input Jhon and 30, the script prints Name: John and Age: 30 in the terminal.

Case 03: Variable Assignment Using Positional Parameters

In Bash, you can assign values to variables using positional parameters. Positional parameters are special variables that hold arguments passed to the script when it is executed. They are referenced by their position, starting from $0 for the script name, $1 for the first argument, $2 for the second argument, and so on. To do the same use the below script.

Script (var_command_line.sh) >

#!/bin/bash
# Prompt the user for input
name=$1
age=$2

# Printing the variables
echo "Name: $name"
echo "Age: $age"

Now, run the following command into your terminal to execute the script.

./var_command_line.sh John 30

Upon execution of the Bash file, the script takes two command-line arguments, John and 30, and returns the output Name: John and Age: 30 in the command line.

Case 04:  Environment Variables and Variable Scope

In Bash script, Environment Variables are another type of variable. Those variables are available in the current session and its child processes once you export your own variable in the environment. However, you can access those and scope it to a function. Here’s a sample Bash script code of environment variables and variable scope describing the concept.

Script (var_scope.sh) >

#!/bin/bash
# Environment variable assignment
export MY_VARIABLE="Hello, World!"

# Function with a local variable

my_function() {
  local local_var="I am a local variable"
  echo "Function Output: $local_var"
}

# Printing the environment variable and calling the function
echo "Environment Variable: $MY_VARIABLE"
my_function

Finally, run the following command into your terminal to execute the bash file.

./var_scope.sh

Upon printing the My_VARIABLE and calling the my_function, the code returns “Environment Variable: Hello, World” and “I am a local variable” respectively.

Conclusion

In conclusion, variable declaration and assignment is a very straightforward process and does not take any extra effort to declare the variable first, just like the Python programming language. In this article, I have tried to give you a guideline on how to declare and assign variables in a Bash Scripts. I have also provided some practical cases related to this topic. However, if you have any questions or queries regarding this article, feel free to comment below. I will get back to you soon. Thank You!

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