How do you substitute on previous matches?

Question

For example, if I have the following:

MY_VAR = "hello world"
print "the var %s" % MY_VAR

If I position the cursor on MY_VAR and press *, Vim highlights both matches. Suppose I want to rename this to HELLO_WORLD_VAR, how might I achieve this?

Answer 1

Since you pressed *, your last search was for MY_VAR, i.e. equivalent to /MY_VAR. If you don't specify a search pattern in a substitution, the last search pattern is used, which is MY_VAR in your case. So you can simply use :%s//HELLO_WORLD_VAR/g to do the renaming.

Note that I used the g flag to indicate that all occurences should be replaced, not only the first on any line. It's not neccessary in your case, but probably makes sense in another context.