Remove empty lines from a file

Question

I'm able to find empty lines with /^$, but when I go to remove them using :%s/^$//, nothing seems to happen. Yet, some form of substitution is being made, because the status line reads XX substitutions on XX lines where XX is the number of empty lines in the file.

Questions:

1. What substitutions are being made, as indicated by the status line?
2. How do I accomplish what I want to do (eliminate empty lines from a file)?

Answer 1

1. ^ and $ are zero-width items, so when you do :%s/^$// you’re substituting zero characters for zero characters
2. To actually perform the substitution, the idioms are

:g/^$/d

and

:g/^$/j