linux - What is the difference between "./somescript.sh" and ". ./somescript.sh"

Question

Today I was following some instructions to install a software in Linux. There was a script that needs to be run first. It sets some environment variables.

The instruction told me to execute . ./setup.sh, but I made a mistake by executing ./setup.sh. So the env was not set. Finally I noticed this and proceeded.

I want to know the difference between these two methods of invoking a script. I am completely new to Linux so please be as elaborate as possible.

Answer 1

./setup.sh runs the script, a new shell will be started that runs the script. That new shell cannot affect the parent shell that started the script.

. ./setup.sh is a shorthand for source ./setup.sh and it will run the script in the current shell, instead of starting a new shell to run it. This means the script can alter the behavior of the current shell, e.g. set new environment variables.