How do you add two variables in Shell?

Use the following syntax to calculate the sum of two integers in a shell script:

1. Using expr command with quotes sum=`expr $num1 + $num2`
2. Use expr command inclosed with brackets and start with dollar symbol. sum=$(expr $num1 + $num2)
3. This is my preferred way to directly with the shell. sum=$(($num1 + $num2))

How add variable in Linux?

d, where you will find a list of files that are used to set environment variables for the entire system.

1. Create a new file under /etc/profile. d to store the global environment variable(s). …
2. Open the default profile into a text editor. sudo vi /etc/profile.d/http_proxy.sh.
3. Save your changes and exit the text editor.