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 sometimes see the assignment expansion with the : command:

# set defaults
: ${foo:=bar} ${baz:=qux}