Single dot (.) represents the directory you are in and double dot (.. ) represents the parent directory.
So ./A refers to a file that ought to be in your current working directory. The dot (.) operator is also known as source. In the below example, first dot is the command source to read and execute commands from the filename given as argument. The second dot is the current directory. So dot operator is a shortcut for the shell’s built-in source command.
. ./setup.sh # Above is the same as source ./setup.sh # Above is the same as source setup.sh
Double dot also refers to parent directory. It can used in cd command for moving around directory. For example, to go to the ‘mnt’ which at third level from the current directory use below syntax.
cd ../../mnt
Directory with Dot
Files and directories whose names begin with a dot by default are not displayed in directory listings by the ls command. Therefore, they are traditionally used to store settings, preferences.
Dot and Double dot are two special directory names in Linux. Directory named . is an alias for the same directory in which it appears (a self reference). Directory named .. refers to the parent directory of current directory.