variable assignment in shell

How-To Geek

How to work with variables in bash.

Want to take your Linux command-line skills to the next level? Here's everything you need to know to start working with variables.

Hannah Stryker / How-To Geek

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Variables 101, examples of bash variables, how to use bash variables in scripts, how to use command line parameters in scripts, working with special variables, environment variables, how to export variables, how to quote variables, echo is your friend, key takeaways.

Variables are named symbols representing strings or numeric values. They are treated as their value when used in commands and expressions.
Variable names should be descriptive and cannot start with a number or contain spaces. They can start with an underscore and can have alphanumeric characters.
Variables can be used to store and reference values. The value of a variable can be changed, and it can be referenced by using the dollar sign $ before the variable name.

Variables are vital if you want to write scripts and understand what that code you're about to cut and paste from the web will do to your Linux computer. We'll get you started!

Variables are named symbols that represent either a string or numeric value. When you use them in commands and expressions, they are treated as if you had typed the value they hold instead of the name of the variable.

To create a variable, you just provide a name and value for it. Your variable names should be descriptive and remind you of the value they hold. A variable name cannot start with a number, nor can it contain spaces. It can, however, start with an underscore. Apart from that, you can use any mix of upper- and lowercase alphanumeric characters.

Here, we'll create five variables. The format is to type the name, the equals sign = , and the value. Note there isn't a space before or after the equals sign. Giving a variable a value is often referred to as assigning a value to the variable.

We'll create four string variables and one numeric variable,

my_name=Dave

my_boost=Linux

his_boost=Spinach

this_year=2019

To see the value held in a variable, use the echo command. You must precede the variable name with a dollar sign $ whenever you reference the value it contains, as shown below:

echo $my_name

echo $my_boost

echo $this_year

Let's use all of our variables at once:

echo "$my_boost is to $me as $his_boost is to $him (c) $this_year"

The values of the variables replace their names. You can also change the values of variables. To assign a new value to the variable, my_boost , you just repeat what you did when you assigned its first value, like so:

my_boost=Tequila

If you re-run the previous command, you now get a different result:

So, you can use the same command that references the same variables and get different results if you change the values held in the variables.

We'll talk about quoting variables later. For now, here are some things to remember:

A variable in single quotes ' is treated as a literal string, and not as a variable.
Variables in quotation marks " are treated as variables.
To get the value held in a variable, you have to provide the dollar sign $ .
A variable without the dollar sign $ only provides the name of the variable.

You can also create a variable that takes its value from an existing variable or number of variables. The following command defines a new variable called drink_of_the_Year, and assigns it the combined values of the my_boost and this_year variables:

drink_of-the_Year="$my_boost $this_year"

echo drink_of_the-Year

Scripts would be completely hamstrung without variables. Variables provide the flexibility that makes a script a general, rather than a specific, solution. To illustrate the difference, here's a script that counts the files in the /dev directory.

Type this into a text file, and then save it as fcnt.sh (for "file count"):

#!/bin/bashfolder_to_count=/devfile_count=$(ls $folder_to_count | wc -l)echo $file_count files in $folder_to_count

Before you can run the script, you have to make it executable, as shown below:

chmod +x fcnt.sh

Type the following to run the script:

This prints the number of files in the /dev directory. Here's how it works:

A variable called folder_to_count is defined, and it's set to hold the string "/dev."
Another variable, called file_count , is defined. This variable takes its value from a command substitution. This is the command phrase between the parentheses $( ) . Note there's a dollar sign $ before the first parenthesis. This construct $( ) evaluates the commands within the parentheses, and then returns their final value. In this example, that value is assigned to the file_count variable. As far as the file_count variable is concerned, it's passed a value to hold; it isn't concerned with how the value was obtained.
The command evaluated in the command substitution performs an ls file listing on the directory in the folder_to_count variable, which has been set to "/dev." So, the script executes the command "ls /dev."
The output from this command is piped into the wc command. The -l (line count) option causes wc to count the number of lines in the output from the ls command. As each file is listed on a separate line, this is the count of files and subdirectories in the "/dev" directory. This value is assigned to the file_count variable.
The final line uses echo to output the result.

But this only works for the "/dev" directory. How can we make the script work with any directory? All it takes is one small change.

Many commands, such as ls and wc , take command line parameters. These provide information to the command, so it knows what you want it to do. If you want ls to work on your home directory and also to show hidden files , you can use the following command, where the tilde ~ and the -a (all) option are command line parameters:

Our scripts can accept command line parameters. They're referenced as $1 for the first parameter, $2 as the second, and so on, up to $9 for the ninth parameter. (Actually, there's a $0 , as well, but that's reserved to always hold the script.)

You can reference command line parameters in a script just as you would regular variables. Let's modify our script, as shown below, and save it with the new name fcnt2.sh :

#!/bin/bashfolder_to_count=$1file_count=$(ls $folder_to_count | wc -l)echo $file_count files in $folder_to_count

This time, the folder_to_count variable is assigned the value of the first command line parameter, $1 .

The rest of the script works exactly as it did before. Rather than a specific solution, your script is now a general one. You can use it on any directory because it's not hardcoded to work only with "/dev."

Here's how you make the script executable:

chmod +x fcnt2.sh

Now, try it with a few directories. You can do "/dev" first to make sure you get the same result as before. Type the following:

./fnct2.sh /dev

./fnct2.sh /etc

./fnct2.sh /bin

You get the same result (207 files) as before for the "/dev" directory. This is encouraging, and you get directory-specific results for each of the other command line parameters.

To shorten the script, you could dispense with the variable, folder_to_count , altogether, and just reference $1 throughout, as follows:

#!/bin/bash file_count=$(ls $1 wc -l) echo $file_count files in $1

We mentioned $0 , which is always set to the filename of the script. This allows you to use the script to do things like print its name out correctly, even if it's renamed. This is useful in logging situations, in which you want to know the name of the process that added an entry.

The following are the other special preset variables:

$# : How many command line parameters were passed to the script.
$@ : All the command line parameters passed to the script.
$? : The exit status of the last process to run.
$$ : The Process ID (PID) of the current script.
$USER : The username of the user executing the script.
$HOSTNAME : The hostname of the computer running the script.
$SECONDS : The number of seconds the script has been running for.
$RANDOM : Returns a random number.
$LINENO : Returns the current line number of the script.

You want to see all of them in one script, don't you? You can! Save the following as a text file called, special.sh :

#!/bin/bashecho "There were $# command line parameters"echo "They are: $@"echo "Parameter 1 is: $1"echo "The script is called: $0"# any old process so that we can report on the exit statuspwdecho "pwd returned $?"echo "This script has Process ID $$"echo "The script was started by $USER"echo "It is running on $HOSTNAME"sleep 3echo "It has been running for $SECONDS seconds"echo "Random number: $RANDOM"echo "This is line number $LINENO of the script"

Type the following to make it executable:

chmod +x special.sh

Now, you can run it with a bunch of different command line parameters, as shown below.

Bash uses environment variables to define and record the properties of the environment it creates when it launches. These hold information Bash can readily access, such as your username, locale, the number of commands your history file can hold, your default editor, and lots more.

To see the active environment variables in your Bash session, use this command:

If you scroll through the list, you might find some that would be useful to reference in your scripts.

When a script runs, it's in its own process, and the variables it uses cannot be seen outside of that process. If you want to share a variable with another script that your script launches, you have to export that variable. We'll show you how to this with two scripts.

First, save the following with the filename script_one.sh :

#!/bin/bashfirst_var=alphasecond_var=bravo# check their valuesecho "$0: first_var=$first_var, second_var=$second_var"export first_varexport second_var./script_two.sh# check their values againecho "$0: first_var=$first_var, second_var=$second_var"

This creates two variables, first_var and second_var , and it assigns some values. It prints these to the terminal window, exports the variables, and calls script_two.sh . When script_two.sh terminates, and process flow returns to this script, it again prints the variables to the terminal window. Then, you can see if they changed.

The second script we'll use is script_two.sh . This is the script that script_one.sh calls. Type the following:

#!/bin/bash# check their valuesecho "$0: first_var=$first_var, second_var=$second_var"# set new valuesfirst_var=charliesecond_var=delta# check their values againecho "$0: first_var=$first_var, second_var=$second_var"

This second script prints the values of the two variables, assigns new values to them, and then prints them again.

To run these scripts, you have to type the following to make them executable:

chmod +x script_one.shchmod +x script_two.sh

And now, type the following to launch script_one.sh :

./script_one.sh

This is what the output tells us:

script_one.sh prints the values of the variables, which are alpha and bravo.
script_two.sh prints the values of the variables (alpha and bravo) as it received them.
script_two.sh changes them to charlie and delta.
script_one.sh prints the values of the variables, which are still alpha and bravo.

What happens in the second script, stays in the second script. It's like copies of the variables are sent to the second script, but they're discarded when that script exits. The original variables in the first script aren't altered by anything that happens to the copies of them in the second.

You might have noticed that when scripts reference variables, they're in quotation marks " . This allows variables to be referenced correctly, so their values are used when the line is executed in the script.

If the value you assign to a variable includes spaces, they must be in quotation marks when you assign them to the variable. This is because, by default, Bash uses a space as a delimiter.

Here's an example:

site_name=How-To Geek

Bash sees the space before "Geek" as an indication that a new command is starting. It reports that there is no such command, and abandons the line. echo shows us that the site_name variable holds nothing — not even the "How-To" text.

Try that again with quotation marks around the value, as shown below:

site_name="How-To Geek"

This time, it's recognized as a single value and assigned correctly to the site_name variable.

It can take some time to get used to command substitution, quoting variables, and remembering when to include the dollar sign.

Before you hit Enter and execute a line of Bash commands, try it with echo in front of it. This way, you can make sure what's going to happen is what you want. You can also catch any mistakes you might have made in the syntax.

Shell Scripting
Docker in Linux
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Linux interview question
Introduction to Linux Shell and Shell Scripting

Introduction to Shell Scripting

How to Create a Shell Script in linux
Different Shells in Linux
Basic Shell Commands in Linux
Linux Directory Structure
Input Output Redirection in Linux

Variables and Data Types

Shell Scripting - Shell Variables
Shell Scripting - Rules for Naming Variable Name
String Manipulation in Shell Scripting
Array Basics in Shell Scripting | Set 1

Control Structures

Conditional Statements | Shell Script
Looping Statements | Shell Script
Break and Continue Keywords in Linux with Examples

Functions and Script Organization

Shell Scripting - Functions and it's types
How To Pass and Parse Linux Bash Script Arguments and Parameters

Input And Output

Shell Scripting - Standard Input, Output and Error
Shell Script to Perform Operations on a File

Command-Line Arguments and Options

Shell Script to Demonstrate Special Parameters With Example

Error Handling and Debugging

User Space Debugging Tools in Linux
Shell Scripting - System Logging

Regular Expressions

How to Use Regular Expressions (RegEx) on Linux

Advanced Topics

Shell Scripting - Interactive and Non-Interactive Shell

Scripting Best Practices

Comments in Shell Script

Shell Scripting Examples and Projects

Shell script to display Good Morning, Good Afternoon Good Evening according to system time

Shell Scripting – Shell Variables

A shell variable is a character string in a shell that stores some value. It could be an integer, filename, string, or some shell command itself. Basically, it is a pointer to the actual data stored in memory. We have a few rules that have to be followed while writing variables in the script (which will be discussed in the article). Overall knowing the shell variable scripting leads us to write strong and good shell scripts.

Rules for variable definition

A variable name could contain any alphabet (a-z, A-Z), any digits (0-9), and an underscore ( _ ). However, a variable name must start with an alphabet or underscore. It can never start with a number. Following are some examples of valid and invalid variable names:

Valid Variable Names
Invalid variable names

Note: It must be noted that no other special character except underscore can be used in a variable name because all other special characters have special meanings in Shell Scripting.

Defining Variables

These kinds of variables are scalar variables as they could hold one value at a time.

1) Accessing variable

Variable data could be accessed by appending the variable name with ‘$’ as follows:

Example of Accessing variable

2) Unsetting Variables

The unset command directs a shell to delete a variable and its stored data from list of variables. It can be used as follows:

Example of Unsetting Variables

Note: The unset command could not be used to unset read-only variables.

3) Read only Variables.

These variables are read only i.e., their values could not be modified later in the script. Following is an example:

Example of Read only Variables.

Now let us see all the above codes in action together. Following is a shell script that includes all the shell variables discussed above.

All outputs

Variable Types

We can discuss three main types of variables:

1) Local Variable:

Variables which are specific to the current instance of shell. They are basically used within the shell, but not available for the program or other shells that are started from within the current shell.

For example:

`name=Jayesh`

In this case the local variable is (name) with the value of Jayesh. Local variables is temporary storage of data within a shell script.

2) Environment Variable:

These variables are commonly used to configure the behavior script and programs that are run by shell. Environment variables are only created once, after which they can be used by any user.

For example:

`export PATH=/usr/local/bin:$PATH` would add `/usr/local/bin` to the beginning of the shell’s search path for executable programs.

3) Shell Variables:

Variables that are set by shell itself and help shell to work with functions correctly. It contains both, which means it has both, some variables are Environment variable, and some are Local Variables.

`$PWD` = Stores working directory

`$HOME` = Stores user’s home directory

`$SHELL` = Stores the path to the shell program that is being used.

Few more examples in Shell Scripting and Shell Variable

How to store user data in a variable.

In this example the variables ‘length’, ‘width’ and ‘area’ are used to store user input and calculate the area of the rectangle.

Giving input to the variable

In this ‘echo’ is a command used to print the statement and ‘read’ is a command used to take data from user and store it in a variable.

To Store and Display Message

We can write a script in which we will display a message to the user by looking at the time of the day. In this we can use shell variable to store and display our message.

Getting output based on the time of the day.

In this ‘time’ is a variable storing hours, ‘data’ is a command used to get the current time and ‘%H’ is used to extract only hour’s part. ‘-lt’ is an operator used for numerical comparison it is a less than. ‘fi’ is used to mark the end of ‘if’ statement.

What is Shell and Its Type?

It is a program that provides a user interface that is used to access operating system services. Or we can say that it is an environment in which we can run our programs and shell scripts etc. It is the core of the operating system.

There are several different types of shell available. Some common types of shells include:

Bourne Shell (sh): The original shell of UNIX operating system. It has been used for scripting purposes and also to provide basic commands.
C Shell (csh): This is also a popular shell for UNIX operating system. As the name suggests, its syntax is similar to C programming language.
Bourne-Again Shell (bash): It is a widely used shell for macOS and Linux operating systems. It is more advanced than the original Bourne shell and also has many features that are found in the Korn shell and C shell.

What is Shell Variable Used For?

Shell Variables are used to store data and information within a shell (terminal), and they are also used for controlling the behavior of program and scripts. Some of the common uses are:

Setting environment variables.
Storing configuration data.
Storing temporary data.
Passing arguments to scripts.

What is Shell Variable and Shell Scripting?

Shell Variable is used in shell scripts for many functionalities like storing data and information, taking input from users, printing values that are stored. They are also used for storing data temporarily and storing output of commands.

Shell Scripting is a way of writing scripts of programs that are executed in a terminal or shell. Basically, it is a program or script which is written with the help of variables mentioned in it. It is powerful because it can automate tasks, and in this one can use programming constructs that are available in shell, such as loops, conditionals and functions.

Conclusion:

Shell variables are an essential part of shell scripting. Shell variables allow us to use them anywhere in the script. In this article we have discussed the rules for defining scalar variables, unsetting variables, read-only variables and accessing variables. This article will serve as a helpful guide for beginners and those who want to understand how to write shell script must know how to work with shell variables.

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The Shell Scripting Tutorial

Variables - part 1.

Just about every programming language in existence has the concept of variables - a symbolic name for a chunk of memory to which we can assign values, read and manipulate its contents. The Bourne shell is no exception, and this section introduces that idea. This is taken further in Variables - Part II which looks into variables which are set for us by the environment. Let's look back at our first Hello World example. This could be done using variables (though it's such a simple example that it doesn't really warrant it!) Note that there must be no spaces around the " = " sign: VAR=value works; VAR = value doesn't work. In the first case, the shell sees the " = " symbol and treats the command as a variable assignment. In the second case, the shell assumes that VAR must be the name of a command and tries to execute it. If you think about it, this makes sense - how else could you tell it to run the command VAR with its first argument being "=" and its second argument being "value"? Enter the following code into var.sh:

This assigns the string "Hello World" to the variable MY_MESSAGE then echo es out the value of the variable. Note that we need the quotes around the string Hello World. Whereas we could get away with echo Hello World because echo will take any number of parameters, a variable can only hold one value, so a string with spaces must be quoted so that the shell knows to treat it all as one. Otherwise, the shell will try to execute the command World after assigning MY_MESSAGE=Hello

The shell does not care about types of variables; they may store strings, integers, real numbers - anything you like. People used to Perl may be quite happy with this; if you've grown up with C, Pascal, or worse yet Ada, this may seem quite strange. In truth, these are all stored as strings, but routines which expect a number can treat them as such. If you assign a string to a variable then try to add 1 to it, you will not get away with it:

This is because the external program expr only expects numbers. But there is no syntactic difference between:

Note though that special characters must be properly escaped to avoid interpretation by the shell. This is discussed further in Chapter 6, Escape Characters .

We can interactively set variable names using the read command; the following script asks you for your name then greets you personally:

Mario Bacinsky kindly pointed out to me that I had originally missed out the double-quotes in the final line, which meant that the single-quote in the word "you're" was unmatched, causing an error. It is this kind of thing which can drive a shell programmer crazy, so watch out for them!

Scope of Variables

Variables in the Bourne shell do not have to be declared, as they do in languages like C. But if you try to read an undeclared variable, the result is the empty string. You get no warnings or errors. This can cause some subtle bugs - if you assign MY_OBFUSCATED_VARIABLE=Hello and then echo $MY_OSFUCATED_VARIABLE Then you will get nothing (as the second OBFUSCATED is mis-spelled).

There is a command called export which has a fundamental effect on the scope of variables. In order to really know what's going on with your variables, you will need to understand something about how this is used.

Create a small shell script, myvar2.sh :

Now run the script:

MYVAR hasn't been set to any value, so it's blank. Then we give it a value, and it has the expected result. Now run:

It's still not been set! What's going on?! When you call myvar2.sh from your interactive shell, a new shell is spawned to run the script. This is partly because of the #!/bin/sh line at the start of the script, which we discussed earlier . We need to export the variable for it to be inherited by another program - including a shell script. Type:

Now look at line 3 of the script: this is changing the value of MYVAR . But there is no way that this will be passed back to your interactive shell. Try reading the value of MYVAR :

Once the shell script exits, its environment is destroyed. But MYVAR keeps its value of hello within your interactive shell. In order to receive environment changes back from the script, we must source the script - this effectively runs the script within our own interactive shell, instead of spawning another shell to run it. We can source a script via the "." (dot) command:

The change has now made it out into our shell again! This is how your .profile or .bash_profile file works, for example. Note that in this case, we don't need to export MYVAR . An easy mistake to make is to say echo MYVAR instead of echo $MYVAR - unlike most languages, the dollar ( $ ) symbol is required when getting the value of a variable, but must not be used when setting the value of the variable. An easy mistake to make when starting out in shell scripting. One other thing worth mentioning at this point about variables, is to consider the following shell script:

Think about what result you would expect. For example, if you enter "steve" as your USER_NAME, should the script create steve_file ? Actually, no. This will cause an error unless there is a variable called USER_NAME_file . The shell does not know where the variable ends and the rest starts. How can we define this? The answer is, that we enclose the variable itself in curly brackets :

The shell now knows that we are referring to the variable USER_NAME and that we want it suffixed with " _file ". This can be the downfall of many a new shell script programmer, as the source of the problem can be difficult to track down.

Also note the quotes around "${USER_NAME}_file" - if the user entered "Steve Parker" (note the space) then without the quotes, the arguments passed to touch would be Steve and Parker_file - that is, we'd effectively be saying touch Steve Parker_file , which is two files to be touch ed, not one. The quotes avoid this. Thanks to Chris for highlighting this.

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Home > Bash Scripting Tutorial > Bash Variables > Variable Declaration and Assignment

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 : Opens a file in the Nano text editor.
basic_var.sh : Name of the file.

❸ Copy the script mentioned below:

The script starts with the shebang line ( #!/bin/bash ), specifying that the script should be executed using the Bash shell . Next, two variables are declared and assigned values using the format variable_name = value . The first variable is name , and it is assigned the string value “ John .” The second variable is age , assigned the numeric value 30 . The script then uses the echo command to print the values of the variables.

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 : is used to change the permissions of files and directories.
u+x : Here, u refers to the “ user ” or the owner of the file and +x specifies the permission being added, in this case, the “ execute ” permission. When u+x is added to the file permissions, it grants the user ( owner ) permission to execute ( run ) the file.
basic_var.sh : File name to which the permissions are being applied.

❻ Run the script by the following command:

Basic Variable Assignment in Bash Script

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:

You can follow the steps of Case 01 , to create, save and make the script executable.

Script (user_var.sh) >

The script starts with the shebang line ( #!/bin/bash ) to specify that the Bash shell should be used for executing the script. The read command is then used twice, each with the -p option, to prompt the user for input. Both the name and age variables take the name and age of the user and store them in the name and age variable with the help of the read command . Then the script uses the echo command to print the values of the variable’s name and age , respectively. The $ name and $age syntax are used to access the values stored in the variables and display them in the output.

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

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) >

The script starts with the shebang line ( #!/bin/bash ) to specify that the Bash shell should be used for executing the script. The script uses the special variables $1 and $2, which represent the first and second command – line arguments , respectively, and assigns their values to the name and age variables . The $ name and $age syntax are used to access the values stored in the variables and display them using the echo command .

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

Variable Assignment Using Positional Parameters

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) >

The script starts with the shebang line ( #!/bin/bash ) to specify that the Bash shell should be used for executing the script. Then, an environment variable named MY_VARIABLE is assigned the value “ Hello, World! ” using the export command . The script also defines a Bash function called my_function . Inside this function, a local variable named local_var is declared using the local keyword . After defining the function, the script proceeds to print the value of the environment variable MY_VARIABLE , which is accessible throughout the script. Upon calling the my_function , it prints the value of the local variable local_var , demonstrating its local scope .

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

Environment Variables and Variable Scope

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

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!

Mohammad Shah Miran

Hey, I'm Mohammad Shah Miran, previously worked as a VBA and Excel Content Developer at SOFTEKO, and for now working as a Linux Content Developer Executive in LinuxSimply Project. I completed my graduation from Bangladesh University of Engineering and Technology (BUET). As a part of my job, i communicate with Linux operating system, without letting the GUI to intervene and try to pass it to our audience.

How to Assign One Variable to Another in Bash

Linux Howtos
How to Assign One Variable to Another in …

Declare a Variable in Bash

Assign one variable to another in bash.

In Bash, a variable is created by giving its reference a value. Although the built-in declare statement in Bash is not required to declare a variable directly, it is frequently used for more advanced variable management activities.

To define a variable, all you have to do is give it a name and a value. Your variables should have descriptive names that remind you of their relevance. A variable name cannot contain spaces or begin with a number.

However, it can begin with an underscore. Apart from that, any combination of uppercase and lowercase alphanumeric characters is permitted.

To create a variable in the Bash shell, you must assign a value to that variable.

Here, varname is the name of the newly created variable, and value is the value assigned to the variable. A value can be null.

Let’s look at an example.

Using the echo command, we can see the value of a variable. Whenever you refer to the value of a variable, you must prefix it with the dollar symbol $ , as seen below.

Let’s put all of our variables to work at the same time.

We can run dest=$source to assign one variable to another. The dest denotes the destination variable, and $source denotes the source variable.

Let’s assign variable a to variable b .

Hence, we can easily assign the value of one variable to another using the syntax above.