Ubuntu – How to show the full path of a file or directory in the terminal

No, your assumption is wrong. The full path name for my_script file from your home directory is: /home/your_user_name/my_script. When you type ./my_script in terminal you actually try to execute the script (if is executable) and it will be executed only if your current working directory is /home/your_user_name/. To execute the script you can use also the full file path which is, as I said /home/your_user_name/my_script.

It is believed that a UNIX path name looks and feels like Internet addresses, thus result into compatibility. The full path name of the current working directory can be found in terminal by using the following command:

pwd

To find out the full path for your user home directory, you can use:

echo ~
echo $HOME
echo /home/$USER

The above three commands are equivalent.

To find out the full path name for a file you can use readlink command. For example, in your case:

cd ~
readlink -f my_script

The max filename length is 255 bytes. Found in the wiki page for ext4.

And a maximum path of 4096 characters. Found in this Unix&Linux SE Question.

Although, I did find this wiki article that does not specify a max file path in ext4.