What is the difference between “var=${var:-word}” and “var=${var:=word}”?

Question

I read the bash man page on this, but I do not understand the difference. I tested both of them out and they seem to produce the exact same results.

I want to set a

Answer 1

You cannot see the difference with your examples as you're using var two times, but you can see it with two different variables:

foo=${bar:-something}

echo $foo # something
echo $bar # no assignement to bar, bar is still empty

foo=${bar:=something}

echo $foo # something
echo $bar # something too, as there's an assignement to bar