004-bash-variables.md

Bash Variables

As in any other programming language, you can use variables in Bash Scripting as well. However, there are no data types, and a variable in Bash can contain numbers as well as characters.

To assign a value to a variable, all you need to do is use the = sign:

name="DevDojo"

{notice} as an important note, you can not have spaces before and after the = sign.

After that, to access the variable, you have to use the $ and reference it as shown below:

echo $name

Wrapping the variable name between curly brackets is not required, but is considered a good practice, and I would advise you to use them whenever you can:

echo ${name}

The above code would output: DevDojo as this is the value of our name variable.

Next, let's update our devdojo.sh script and include a variable in it.

Again, you can open the file devdojo.sh with your favorite text editor, I'm using nano here to open the file:

nano devdojo.sh

Adding our name variable here in the file, with a welcome message. Our file now looks like this:

#!/bin/bash

name="DevDojo"

echo "Hi there $name"

Save it and run the file using the command below:

./devdojo.sh

You would see the following output on your screen:

Hi there DevDojo

Here is a rundown of the script written in the file:

• #!/bin/bash - At first, we specified our shebang.
• name=DevDojo - Then, we defined a variable called name and assigned a value to it.
• echo "Hi there $name" - Finally, we output the content of the variable on the screen as a welcome message by using echo

You can also add multiple variables in the file as shown below:

#!/bin/bash

name="DevDojo"
greeting="Hello"

echo "$greeting $name"

Save the file and run it again:

./devdojo.sh

You would see the following output on your screen:

Hello DevDojo

Note that you don't necessarily need to add semicolon ; at the end of each line. It works both ways, a bit like other programming language such as JavaScript!

You can also add variables in the Command Line outside the Bash script and they can be read as parameters:

./devdojo.sh Bobby buddy!

This script takes in two parameters Bobbyand buddy! separated by space. In the devdojo.sh file we have the following:

#!/bin/bash

echo "Hello there" $1

$1 is the first input (Bobby) in the Command Line. Similarly, there could be more inputs and they are all referenced to by the $ sign and their respective order of input. This means that buddy! is referenced to using $2. Another useful method for reading variables is the $@ which reads all inputs.

So now let's change the devdojo.sh file to better understand:

#!/bin/bash

echo "Hello there" $1

# $1 : first parameter

echo "Hello there" $2

# $2 : second parameter

echo "Hello there" $@

# $@ : all

The output for:

./devdojo.sh Bobby buddy!

Would be the following:

Hello there Bobby
Hello there buddy!
Hello there Bobby buddy!