unix command line execute with . (dot) vs. without

Question

At a unix command line, what\'s the difference between executing a program by simply typing it\'s name, vs. executing a program by typing a . (dot) followed by the program n

Answer 1

Running "runme" will create a new process which will go on its merry little way and not affect your shell.

Running ". runme" will allow the script "runme" to change your environment variables, change directories, and all sorts of other things that you might want it to do for you. It can only do this because it's being interpreted by the shell process that's already running for you. As a consequence, if you're running bash as your login shell, you can only use the "." notation with a bash script, not (for example) a binary on C shell script.