Variables in the Linux terminal
Local variables
Creating one
Creating a local variable is simple by typing:
local_variable_name=value
To create a variable that stores the number one for example, you type:
number_one=1
To make sure a variable is created, you use the echo command and a dollar sign before the name of the variable:
echo $local_variable_name
Going back to our number_one variable, to see if it's created, you type:
echo $number_one
In turn, the terminal should just display the number one:
1
Global variables
Creating one
You create a global variable by typing:
export global_variable_name=value
So to create a global variable storing the number two for example, you type:
export number_two=2
To check if a global variable is created, you use the same process on checking if a local variable is created. That being using the echo command:
echo $global_variable_name
So to check if the variable number_two is created, you type:
echo $number_two
In which, the terminal should just display the number two:
2
Check if a variable is global
To see if a variable is actually global, you type:
env | grep variable_name
So for our number_two variable, you type:
env | grep number_two
In which, the terminal should display:
number_two=2
Predefined global variables
There are also already global variables on your system that you never made. Like HOME and PATH for example. And you can display their values using the echo command.
Displaying the value for the global HOME variable for example:
echo $HOME
Will just display the path of your user folder.
Converting local variables into global ones
You can convert a local variable into a global one by typing:
export local_variable_name
Let's create a local variable called number_three for example:
number_three=3
Of course, running:
echo $number_three
Will cause the terminal to display just the number three:
3
However, running:
env | grep number_three
Won't cause the terminal to display anything since number_three isn't a global variable.
To convert number_three to a global variable, you type:
export number_three
Now when you run:
env | grep number_three
The terminal should display:
number_three=3
Deleting variables
To delete a variable, you type:
unset variable_name
This works regardless if the variable is local or global.
So to delete the variable number_three you made, you type:
unset number_three
Now if you type:
echo $number_three
The number three shouldn't be displayed since the number_three variable got deleted.
And because number_three was a global variable, typing:
env | grep number_three
Will not display anything either.