In this tutorial, we’ll explore how to declare variables and perform basic input and output operations in the Linux terminal.
Declaring Variables
To declare variables in Linux, you can use the = assignment operator. Here’s an example:
1name="John"
2age=25
3echo $name $age
Output:
John 25
In the above example, we’ve declared two variables: name and age. The value of name is set to “John”, while the value of age is set to 25.
Using the local keyword
The local keyword allows you to declare a variable with local scope within a function or script. Here’s an example:
1my_function() {
2 local variable_name="value"
3}
In the above example, we define a shell function called my_function. Inside the function, we use the local keyword to declare a variable named variable_name and assign it the value “value”.
Note that variables declared with local are only accessible within the function or script in which they are defined.
Using the let keyword
The let keyword is used for arithmetic operations and variable assignment. It allows you to perform calculations and update variable values in a concise manner. Here’s an example:
1let "result = 5 + 3"
In this example, we use the let keyword to perform addition (5 + 3) and assign the result to the variable named result.
You can also use variables in arithmetic expressions with the help of $ sign:
1a=5
2b=3
3let "result = $a + $b"
This will add the values of variables $a and $b, storing the result in $result.
The advantage of using the let keyword is that it eliminates the need for explicit command substitution or quoting.
When using these keywords, it is important to follow proper syntax rules, including any necessary quotation marks or mathematical expressions.
With this knowledge of declaring variables using local and performing arithmetic operations using let, you can enhance your Linux shell scripts and functions.
You can also assign the output of a command to a variable using command substitution using $.
1current_date=$(date +%Y-%m-%d)
2echo $current_date
In this case, the current date will be stored in the current_date variable. Again, to print the value of a variable we can use echo command and prefix the variable name with $ symbol.
Basic Input and Output
There are basically two methods to accept user input.
Taking User Input
To get input from the user in Linux, you can use either the read command or by passing arguments directly from the command line.
Using the read command:
1read -p "Enter your name: " name
2echo "Hello $name!"
Output:
bash main.sh
Enter your name: George
Hello George!
The -p option allows you to display a prompt message before accepting user input.
Another way to get input is by passing arguments to bash script directly from the command line.
1echo "Hello $1!"
Output:
bash main.sh Alex
Hello Alex
Here, $1 represents the first argument passed to our script or command. You can pass multiple arguments separated by spaces.
Printing output
For displaying output in Linux, you can use the echo or printf commands:
1echo "Hello World"
2printf "Welcome to my blog!"
Both commands will display their respective messages on the terminal.
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