Default way of running scripts in Linux is that shell forks new process based on hashbang (#!) found in the first line and gives rest of content to that process. And this works beautifully most of the time.
But what if we really need something found only in our current shell?
Fortunately, as long you are using bash, it is easy to run script without creating a separate shell. Just prefix it with dot (.):
# . ./myScriptSome restrictions apply of course - the biggest gotcha being that script should be either bash or with only simple commands as content will be executed directly regardless of hash-bang (#!) specified.
PS: Yes, this works with other shells too, I use bash here as it is most common shell by far.