Question

To activate a TurboGears virtualenv (just as an example), you do this:

. bin/activate

Or this:

source bin/activate

1. Why does the current directory “.” work as a command?

2. Why use “source” or “.” at all? Why not simply “bin/activate”?

(I did a little Web searching on this, but “.” and “source” get a lot of bad hits.)

Answer 1

1. . doesn’t mean ‘current directory’ in that context. It’s just shorthand for source.

2. sourcing a script (using . or source) runs the script in your current shell’s context, rather than starting a subshell. That means it can make modifications to your current shell’s environment. Simply running a script can’t do that. Example:

   $ cat script
   VARIABLE=something
   $ echo $VARIABLE
   
   $ ./script 
   $ echo $VARIABLE
   
   $ . ./script
   $ echo $VARIABLE
   something