As Bash is a dynamically typed shell, it understands many different types of variables. So, you don’t have to bother about what kind of variables you need to assign. Having a compact knowledge of Bash variable types is enough to choose the perfect data structure for your operations accordingly. In this article, I’m going to share the basic context of variable types in Bash. Let’s dive into it.
Key Takeaways
- Learning about different variable types in Bash.
- Observing several examples of Bash variable types.
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What Are Bash Variables?
Bash variables are temporary storage where you can store various data types like integers, strings, arrays, etc. They do not need any evident declaration always. In fact, these variables are the essential parts that serve users by being referenced and manipulated in Bash programming.
Types of Bash Variables
There are two types of variables in Bash. They are described below:
- System-defined Variables: System-defined variables are the default and pre-defined variables in Bash. Basically, you can define them in capital letters (UPPER_CASE). These are actually the built-in variables in the Linux Bash shell that are accessible whenever you open a new session.
- User-defined Variables: User-defined variables specify the variables that you create and manipulate as a user. These variables are not predefined by the Bash shell. So, there are no certain rules to write these. You can define them in both UPPER_CASE or LOWER_CASE. These user-defined variables are so versatile to use that you can smoothly manage data as per your preferences during the execution.
2 Cases for Checking Variable Types in Bash
You can check the type of variables you have inserted within your script in the following two manners:
Case 1: Checking Variable Type Using “declare” Command
Using the built-in declare command, you can easily identify the variable types, values, attributes, etc. Here’s the step-by-step procedure for checking the variable type using the “declare” command:
➊ Open your Ubuntu Terminal.
➋ To open a script in the nano text editor, write the command below:
nano declare.sh- nano: A text editor.
- declare.sh: This is a script. Here, I have named the script by ’declare.sh’. You can name any of your choices.
➌ Hereafter, write the following script inside the editor:
Script (declare.sh) >
#!/bin/bash
#Assigning variables
website="LinuxSimply"
number=25
array=(1 3 5 7 9)
#Using 'declare' to check variable types
declare -p website
declare -p number
declare -p arrayHere, ‘#!’ is known as ‘Shebang’ or ‘Hashbang’ in #!/bin/bash. Then, in the lines ‘declare -p website’, ‘declare -p number’, and ‘declare -p array’, the “declare” command displays information about the assigned variables ‘website’, ‘number’, and ‘array’.
➍ Then, press CTRL+S to save the file & press CTRL+X to exit.
➎ After that, use the command below to make the script executable:
chmod u+x declare.sh- chmod: Changes the permission of the files and directories.
- u+x: Adds the executable permission for the user.
- declare.sh: The file which you want to make executable.
➏ Finally, run the script by the following command:
./declare.sh
From the image, you can see the values of the assigned variables in the code. Thus, you can identify what types of variables are there.
Case 2: Checking Variable Type Using Conditional Statements
Another way of checking a variable’s type (whether it’s a string, an integer, or an array) in Bash is using conditional statements. Here’s an example of such a scheme:
Script (conditional.sh) >
#!/bin/bash
variable1="2023"
variable2="LinuxSimply"
var_integer() {
if [[ "$1" =~ ^[0-9]+$ ]]; then
echo "Variable '$1' is an Integer."
else
echo "Variable '$1' is a String."
fi
}
var_integer "$variable1"
var_integer "$variable2"The line ‘if [[ “$1” =~ ^[0-9]+$ ]]; then’ checks if the values inserted to the variables and passed to the ‘var_integer’ function match with ‘^[0-9]+$’. Here, ‘^[0-9]+$’ checks if any string contains only digits (0-9). If the regular expression ‘^[0-9]+$’ matches, and the if condition becomes true the echo command prints the line “Variable ‘$1’ is an Integer.”, otherwise, it moves to the else block and the echo command prints the line “Variable ‘$1’ is a String.”.
Now, run the script by the following command:
./conditional.sh
The above image dictates the types of values that I have assigned to the variables.
Best Practices for Using Various Types of Variables in Bash
Using Bash variables properly can make your script more impactful. Here are some best practices that you need to follow while using different types of variables in Bash:
- Purpose of the Variables: Comment on the purpose of each variable you are going to use. This will be helpful for others and for your future self too to get a clear overview of the variables and code.
- Relevant Variable Names: Try to use relevant and meaningful names for your variables. This will make your code more understandable to the readers.
- Double-quote Variables: Double-quote variable expansions during referencing like “$variable” to avoid word splitting.
- Lowercase Variable Names: Be cautious while naming a variable and try to use lowercase letters for this to avoid overwriting the built-in variables in Bash.
- Variable Declaration with ‘local’: During variable declaration within a function, try to use ‘local’ to limit the variables’ activities within the function.
- Define Variables: To avoid unexpected errors or bugs, always define variables with default values before using them.
- Test Empty Variables: Before further use, apply conditional statements to check if the assigned variables are null. You can use the ‘-n’ or ‘-z’ test in this case.
- Check Exit Status: Check the exit status to handle the Bash error and implement a proper control flow.
- Clear Variables: When the variables are no longer needed, unset them and clean up the memory to avoid clutter.
Conclusion
So far, you have got that Bash variables do not have any fixed type, i.e., they can hold different data types based on their assigned values. And this is one of the best things you’ll find in Bash it supports any kind of assigned variables and helps in manipulating data for interactive shell sessions.
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